Camshaft Upgrade Pros And Cons? Top Answer Update

ace

Drives: On order: Camaro SS/RS, A6, SIM

Joined Date: April 2009 Location: Michigan Contributions: 83 Drives: On Order: Camaro SS/RS, A6, SIM

Reliability of Cam Swaps ) some money for my Camaro. I originally wanted to charge it up, but that’s just a bit more than I’m willing to spend now. So for now it looks like a camera, some headers and a good tune (top up later). I’m in Detroit so the two best deals in my area are Livernois and Vector Motorsports. It seems that Vector costs a bit more money, but I’ve only heard great things about their tuning, so that’s a big plus.

My question…if I make a camera (just a tier 1, both of which offer…nothing too crazy) and headers, how will my reliability be affected? I know this is pretty vague, but I have little experience with this stuff, so I appreciate the input. My car isn’t a daily driver and I won’t be racing it…I probably won’t average more than 4,000 miles a year. I really prefer the S/C route just because it’s an easy install while cam swap is more complicated…especially on the L99.

Thanks again for all thoughts! I’m sssssoooooooooooooooo close to spending some money on my Camaro (my wife says waste). I originally wanted to charge it up, but that’s just a bit more than I’m willing to spend now. So it looks like a camera for now, some headers and a good tune (top up later). I’m in Detroit so the two best deals in my area are Livernois and Vector Motorsports. It seems that Vector costs a bit more money, but I’ve only heard great things about their tuning, so that’s a big plus. My question…if I make a camera (only a Stage 1, both of which offer….nothing too crazy) and headings, how will my reliability be affected? I know this is pretty vague, but I have little experience with this stuff, so I appreciate the input. My car isn’t a daily driver and I won’t be racing it…I probably won’t average more than 4,000 miles a year. I really preferred the S/C route just because it’s an easy install, while cam swap is more involved…especially on the L99. Thanks again for your thoughts!

1100 3/20/09

2000 04/20/09

3000 4/21/09

3300 05/14/09

3400 5/23/09

3800 6/3/09

IN MY GARAGE 06/11/09!!!!!!!!

REBORN FROM LIVERNOIS MOTORSPORTS 05/21/2010! 2010 Camaro SS/RS, A6, SIMREBORN BY LIVERNOIS MOTORSPORTS 05/21/2010! __________________

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Do I need new tappets when changing the camshaft?

When to Replace or Reuse Jacks

Camshafts with flat tappets

New flat follower lifters are ALWAYS required for flat follower cams.

Used flat lifters will show a wear pattern on the face. This wear pattern prevents the jack from rotating properly. It causes heavy wear on both surfaces in a very short time.

The wear pattern on the camshaft and tappets begins during the break-in process. This is one of the reasons why following the break-in procedure is so important. Even if cams and lifters only run for a short time, they are considered used.

roller camshafts

New roller lifters are not always required for roller curves.

If you intend to reuse roll lifters you should:

Thoroughly clean and inspect each jack. Make sure the needle bearings and axle are in good condition and roll smoothly. Inspect the jack body and wheel for cracks, wear, and heat discoloration. Follow the break-in procedure accordingly.

Remarks

Remember, you cannot use a roller lifter with a flat tappet cam. You cannot use flat tappet lifters with a roller cam.

Quote: cranky quote from ever kickstarting a harley engine after a major cam change? have you ever measured compression? You might be surprised at the result.

That is interesting. I’ve swapped a lot of cams on American V8s and measured compression before and after cranking. Each cam with a later intake valve closing point gives less cranking compression pressure than one with an earlier intake valve closing point. And usually (but not always) a “bigger” cam will have a longer intake duration and usually a later intake valve closing point (than stock)…this also depends on the cam centers of course…all grind specific. It’s possible that the high-performance Harley cam you were working with has a “short” intake duration (earlier intake valve closing point) specifically to increase compression (for more low-end power), but a longer one Duration of exhaust to improve torque at high revs etc. Or it’s possible that the Harley cams have a longer intake duration BUT tighter cam centers that would effectively place the intake closing point RELATIVELY earlier even though the duration is longer. I’m not familiar with custom cam loops for Harleys. I know these engines (with offset crankpins) are unique beasts, and I imagine they “require” a less than typical cam grind for optimal performance. The intake close point early enough to get higher cranking compression pressure than the cam that came out (as installed). I did extensive testing at the time using V8 cams to specifically REDUCE static compression pressure so that high compression ratio engines could run on 93 octane pump gas. I’ve swapped and adjusted cams and kept checking the compression pressure… I think I’ve worn out three compression gauges… and several batteries. Always reduced pressure/detonation tendencies when using a “bigger” cam with later intake valve closing points…or you could even just take the existing “small” cam and delay it for the same effect. (But ultimately the “best” way to deal with an over-compression ratio engine (when only 93 octane is available) is to simply reduce the compression ratio…then you can do “optimal” cam grind and spark timing, etc. without detonation.) Considering all of this, you might recall that in the late 70’s (when compression ratios were falling through the bucket) a lot of people were purposefully upgrading their existing cameras, and it would add a nice little noticeable kick towards pants in the lower revs…why? …effective increase in static compression pressure…pretty much the same as a small increase in compression ratio. Advancing the cam naturally closes the intake earlier. I had developed some general formulas for large cubic inch (large stroke) V8 engines based on all my first hand measurements…if I remember correctly setting the intake valve closing point 4 degrees earlier increased cranking compression pressure by about 5psi , and raising the compression ratio by about 1 full point increased crank compression pressure by about 20 psi…or thereabouts…averages. With these very general formulas above in mind, if you were to swap out a “larger” cam with an intake close point 10 degrees later than stock (as installed) you would drop the compression pressure by about 10psi at cranking…this would be almost same as lowering your compression ratio by about half a point in terms of effective pressure. Side note…this information above is NOT based on Chevy small block engines and may not apply exactly to our Corvettes, but I mention all this just as a general example of compression pressure safe factors.

default version:

Grind #XA218/325-XA224/325-16+3

Duration at 0.050 – 218/224

Raise with 1.7 – .553″/.553″.

flap separation 116

Inlet Centerline 113

High-Lift Version:

Grind #XA218/350-XA224/350-16+3

Duration at 0.050 – 218/224

Lift with 1.7 – .595″/.595″

flap separation 116

Inlet Centerline 113

The LS1 Stage 3 camshaft is designed for enthusiasts looking to increase performance while maintaining excellent handling and handling. These cams can be used with stock torque converters, stock rear gears, stock intake manifolds, stock exhaust manifolds, etc. However, additional performance gains can be realized when used with other performance modifications. The Stage 3 LS1 cam is the largest cam we recommend with the stock torque converter. This Cam Motion hydraulic cam offers smooth idle power, excellent low-end torque and extended rpm capabilities over the stock cam. This cam is a good performance replacement for Camaro, Firebird, Corvette and other passenger cars that need more power without the larger cams associated with poor gas mileage. Cam Motion designed this camshaft in a “drop-in” version and a high-lift version. The drop-in cams are designed to be compatible with Chevrolet Performance Beehive valve springs or Performance Aftermarket .600″ or .625″ Lift Beehive springs. The high-lift version can be used with our .625″ lift hive springs or our .660″ lift dual valve spring kits. This camshaft can be used with stock, existing tappets, but used tappets should be inspected for wear, damage or irregularities that could damage your new camshaft.

Like all of our cams, our Mild Performance cams use our renowned smooth, quiet and powerful cams, known throughout the LS community for quiet valvetrain operation and superior valvetrain stability.

What you need to know about cameras.

#1 – The most common camshaft mistake made by humans is to OVERCAM the engine.

#2 – selects a cam that is not compatible with the RPM range we intend to run the engine in.

There are a number of things that affect camera performance.

Cylinder Head Flow Rates: The cylinder heads must allow sufficient air flow as long as the valves are open.

Compression Ratio: The static compression ratio and cam selection should be viewed as a system.

Intake: The intake must also allow enough air to flow to aid in cam and cylinder filling.

Exhaust pipes: In addition to having sufficient flow, the exhaust pipe must also be designed so that the reverse pulse is compatible with the camshaft timing.

Here’s a little clue for you, and that’s the word AIRFLOW. Airflow is everything and the camshaft is the airflow regulator. It determines how much, when and for how long. The result of all camshaft specifications is where in the rev range the engine performs best. Now one more thing before we dive into the mystery and that is that we need to understand our goal here. For the purposes of these articles I am not interested in RACING engines, but street engines and street engines need to develop TORQUE and they need to develop TORQUE in the 2500 to 4500 RPM range as that is the range where we use the engine most often operate in (highway ride). There is a camshaft law that we must observe. – If you have it above you will not have it below and if you have it below you will not have it above. We can’t have everything. With a STREET engine we don’t need it on top, we need something on the bottom, but we really need a mid range. So here we are looking for our torque. Now we also have to look at the bike we ride. A dresser needs more bottom end than an FXR due to weight and wind resistance. Alright, now that we’ve got that all behind us, let’s move on to the camera itself.

Inlet Closing: The inlet closing point has more impact on engine operating characteristics than any of the other three opening and closing points. The earlier it occurs, the greater the cranking pressure. Closing the intake early is critical to low-end torque and throttle response, and provides a broad power curve. It also reduces exhaust emissions while improving fuel economy. As the engine speed increases, the intake charge torque increases. This means that the intake charge continues to flow against the combustion chamber, which rises far beyond UT. The higher the engine’s operating speed, the later the inlet should be closed so that as much charge as possible gets into the combustion chamber. Of course, closing the valve too late will result in significant reversal. It’s a delicate balancing act. In a perfect world, the optimal intake shutoff point would be exactly when the air stopped flowing into the chamber. It would seat the valve quickly and not waste time in the low lift areas where airflow is minimal and no compression build up in the cylinder. It wouldn’t be so fast that the valve would bounce as it closed, which could allow the charge to escape back into the intake port and interfere with the next charge. And in hydraulic road cam applications, it would ensure that the closing ramps are not so fast that they result in noisy operation.

A late-closing intake valve results in poor compression and poor power throughout most of the RPM range.

A semi late closing intake has good midrange and top end, but not the best.

An early closing intake (30-35 degrees) is what we like for a heavy bike because it offers excellent bottom end power and a good midrange.

The intake valve closing point is closely related to the dynamic or “effective” compression ratio of an engine. The compression ratio also depends on the cam duration.

A mild cam with an early intake valve closing point works well at low RPM. However, at high engine speeds, the intake valve closes before the maximum amount of air/fuel mixture has been drawn into the cylinder. As a result, performance at high revs suffers. If a high static compression ratio is used with a mild cam (i.e. early intake valve closing point), the mixture may end up being “over-compressed”. This leads to excessive compression losses, detonation, and can even lead to head gasket or piston failure.

On the other hand, an aggressive cam with a late intake valve closing point works well at high rpm. At low engine speeds, however, the intake valve closes too late to achieve sufficient compression of the intake charge. Torque and power suffer as a result. If a low static compression ratio is used with an aggressive cam (i.e. a late intake valve closing point), the mixture may end up being “under-compressed”. Therefore, a high-performance, long-duration cam should ideally be combined with a higher static compression ratio to allow the engine to benefit from the maximized amount of intake charge at high rpm, made possible by the late intake valve closing, and still achieve sufficient compression of the mixture as a by-product of the dynamic compression ratio.

Deadline again!: The most important cam event. This sets the engine’s effective RPM range and effective dynamic compression. An early close (30 – 38 ABDC) = high dynamic compression, great torque at low to mid-rpm for a very wide powerband, requires less static compression (which means less stress and strain on the engine, less risk of heat damage and detonation, more Reliability) … but the engine speed is limited, the engine “stops pulling” around 4800 rpm. When the closing of the intake valve becomes later (40-45), the power band moves around around 250-300 rpm upwards and narrows slightly unless more static compression is built in (e.g. thinner head gasket). Torque stays about the same, but due to higher RPM, HP increases slightly. Throttle response from idle drops slightly. Head temperatures rise slightly making detonation a realistic risk, fuel management/tuning becomes even more critical. And exhaust pipe diameter, length, and back pressure designs are becoming more influential. The engine rotates through 5000 rpm. Closing the valve even later (+45 ABDC) shifts the powerband far up the rpm scale. Increased static compression is required to achieve any TQ/HP. Typically it exceeds 12:1. Fuel management/tuning is very important to reduce detonation and the risk of heat damage. Higher compression shortens engine life. Since this cam only works well at higher RPM, the other cam specs can benefit and be tweaked for more power. What is lost is smooth idling and some usable power/torque at low to mid-rpm, crisp throttle response from idle, engine heat issues become critical. Think bad quarter-mile dragbike: it won’t idle for crap, pops and snorts until the throttle is almost turned WFO when it finally starts roaring – the engine is barely manageable – but damn what a ride !

The intake closing point has more impact on engine operating characteristics than any of the other three opening and closing points. The earlier it occurs, the greater the cranking pressure. Closing the intake early is critical to low-end torque and throttle response, and provides a broad power curve. It also reduces exhaust emissions while improving fuel economy. As the engine speed increases, the intake charge torque increases. This means that the intake charge continues to flow against the combustion chamber, which rises far beyond UT. The higher the engine’s operating speed, the later the inlet should be closed so that as much charge as possible gets into the combustion chamber. Of course, closing the valve too late will result in significant reversal. It’s a delicate balancing act. In a perfect world, the optimal intake shutoff point would be exactly when the air stopped flowing into the chamber. It would seat the valve quickly and not waste time in the low lift areas where airflow is minimal and no compression build up in the cylinder. It wouldn’t be so fast that the valve would bounce as it closed, which could allow the charge to escape back into the intake port and interfere with the next charge. and in hydraulic road cam applications it would ensure that the closing ramps are not so rapid as to result in noisy operation.

The most important timing event is the intake valve closing angle. The intake closing point determines the minimum speed at which the engine starts to do its best work. The later the intake valves close, the higher the engine speed has to be before the engine “cams up”.

If you have one of the late-closing cam designs installed, say one that closes the intake valves later than 40 degrees, then you can’t expect great performance at 2000 rpm. No carburetor adjustment, ignition timing or exhaust system can change that.

Intake Port: Looking at the intake valve, its opening point is critical to vacuum, throttle response, emissions and gas mileage. At low speeds and high vacuum conditions, premature intake opening during the exhaust stroke can allow exhaust gas reversal back into the intake manifold, affecting intake pulse velocity and contaminating the fresh intake charge. A late-opening intake ensures smooth engine operation at idle and low rpm, and ensures adequate manifold vacuum for proper accessory operation (assuming the other three valve opening and closing points remain appropriate). The air requirement increases with increasing speed. To supply additional air and fuel, the designers open the intake valve earlier, giving the intake charge more time to fill the cylinder. With an early opening intake valve, the exiting exhaust gas at high rpm also helps suck the intake charge through the combustion chamber and out the exhaust – this is good for scavenging residual gas from the cylinder, but also increases fuel economy by scavenging some of it allows the intake charge to escape before combustion and can cause a rough idle.

Early usually means overlap, less throttle response at low to mid rpm, rough idle, more emissions, poor fuel economy. However, by opening the intake valve early, we can slightly increase the volumetric efficiency of the engine…if the heads flow better. This is where stock heads fall short compared to ported heads. However – as with cams – bigger isn’t always better when it comes to ported heads. Large orifices and large valves reduce intake and exhaust velocities, which can cause a variety of problems as well as loss of volumetric efficiency. Most Ported Twin Cam heads with stock diameter valves/seats used with stock intakes and SE or K&N air filters typically flow at their maximum CFM in the vicinity of .350″ – .450″ valve lift. Using a cam with the intake valve open that wide by the time the piston has reached maximum speed maintains maximum intake charge speed – making the most of the impulse charging effect between idle and 3500 rpm. Using a cam with even more lift (+0.500″) will only reduce this effect – and performance (along with unnecessary valve train wear). A stock unported head has a very restrictive exhaust port and therefore limits volumetric efficiency even further and makes a high-lift cam even less effective. One thing to remember about cam timing is that the intake valve opens before top dead center and closes after bottom dead center.

Exhaust Port: Overall, the opening point of the exhaust valve has the least effect on engine performance out of the four opening and closing points. Opening the exhaust valve early reduces torque by relieving cylinder pressure from combustion, which is used to push the piston down. However, the exhaust needs to open early enough to have enough time to flush the cylinder properly. An early-opening exhaust valve can benefit scavenging on high-rpm engines, since most useful cylinder pressure is consumed anyway by the time the piston reaches 90 degrees before bottom dead center on the power stroke.

Opening the exhaust valve later helps at low rpm by keeping pressure on the piston longer and it reduces emissions.

Early opening exhaust – this is where we lose our entire bottom end and our midrange will be lazy, what it will do is run hard on the top.

Half-early opening exhaust. This timing gives us good cylinder scavenging, resulting in cleaner cylinder mixture at high rpm. The bottom end will suffer a bit, but the mid-range will be very good.

If the exhaust closes late we have a narrow rev band here, the low end will be good as will the mid range but we will have a hard to handle engine.

Stock cams typically open the exhaust valve late (36 BBDC) to maximize burn time and pass emissions tests more easily…but suffer from pumping losses as the piston has to work harder to mechanically push out the burned gases. If the cam opens the exhaust valve a little early (40-43 BBDC), we can use the blowdown (the expansion of the burning A/F) to scavenge the cylinder. This gets the burned gasses moving, reducing piston force and lowering pumping losses…up to about 4000 rpm. However, if the cam opens the exhaust valve too early (45+ BBDC), the blowdown will use up much of the expansion pressure of the power stroke drain from idle to about 2500 rpm. RPMs must be higher to overcome the time available for blowdown.

Closing the exhaust: Closing the exhaust valve too late is similar to opening the intake too early – it results in increased overlap, which either restores the intake reversal or causes the intake mixture to exit the exhaust directly. On the other hand, late closing events can help scavenge spent gases from the combustion chamber and provide more vacuum signal to the intake at high rpm. Closing the exhaust valve early results in smoother engine operation. It doesn’t necessarily hurt the top end, especially when combined with a later intake valve opening. As the engine’s operating range increases, designers must move all opening and closing points outward to achieve earlier opening and later closing, or design a more aggressive profile to provide increased area under the curve without increasing seat adjustment. Exhaust valve closing – typically between 4 (early) and 20 (late) degrees ATDC. Closing early = less overlap, closing late = much overlap. Less overlap (exhaust valve closes at 4) makes it easier to pass a smog test, smooth idle, great fuel economy. A slight overlap (exhaust valve closes at 8-12) gives good low-mid power, better throttle response, fair fuel economy and slightly more emissions. And large overlap (exhaust valve closes at 13-20) allows for severe dilution/loss of intake charge (poor emissions), worse fuel economy, rough idle, less throttle response from idle, and accounts for most of the power at higher rpm . Note: The amount of overlap also depends on the opening specifications of the cam’s intake valve.

Closing the exhaust valve early results in smoother engine operation. It doesn’t necessarily hurt the top end, especially when combined with a later intake valve opening. As the engine’s operating range increases, designers must move all opening and closing points outward to achieve earlier opening and later closing, or design a more aggressive profile to provide increased area under the curve without increasing seat adjustment.

Cam Centerline: Cam centerlines give you a relative perspective of how advanced or retarded a cam is in relation to top dead center (TDC). Harley cam profiles typically have an inlet centerline of 98 to 108 degrees. A 98 intake centerline is considered the most advanced and generally gives the most torque. A centerline of 108 gives top-end power.

An exhaust centerline of 112 is the most advanced, while the 102 is the most retarded. Again, an advanced cam delivers low-end power, while the retarded cam expands the power range in the rev range. For convenience, most Harley cams are in the range of 96-108 intake and 112-102 exhaust.

Tailoring the valve opening and closing points on an actual camshaft is accomplished by varying the centerline positions of the lobes, changing the LSA, and refining the profile shape itself. Cam advancement moves both intake and exhaust at the same rate, resulting in earlier valve timing events. Engines typically respond better with a few degrees advance, likely due to the importance of the intake closing point to performance. In racing, advanced camshafts promote torque converter stalling, improve off-line starts in drag races, and help circuit cars exit corners. Cam manufacturers often grind their road cams forward (4 degrees is typical), allowing the end user to take advantage of increased cylinder pressure and still install the cam with the standard marks. Increasing the intake cam centerline from 104 to 106 degrees is considered retarding. All events take place later in the engine cycle. Retarding the cam causes the intake valve to open and close later. This reduces the cylinder pressure, which reduces the engine’s performance at low speeds.

Advancing the intake and retarding the exhaust (‘closing the mids’) increases overlap and should increase power through the rpm range, usually at the expense of bottom-end power. The result would be lower numerical values ​​at both intake and exhaust cam centers.

Retarding the intake and advancing the exhaust (“spreading the mids”) reduces overlap and should result in a wider powerband at the expense of some peak power. This condition would be indicated by higher numerical values ​​at both intake and exhaust cam centers. By moving just one cam the results are less predictable, but usually it is the intake that is moved to change performance characteristics, as small changes here seem to have a larger effect.

Lobe Separation Angle: The lobe separation is the angle between the mid-lobe of the inlet lobe and its counterpart on the outlet lobe. Think of it like the two points of a pair of scissors relative to the hinge in the middle. When the scissors are almost closed, you can cut well as long as you cut thin. To cut thick material you open wider but have less leverage so it can be more difficult to get the job done. The same principle applies to separation at cams. Typically, cam spacing for road cams is between 97 and 108 (camshaft) degrees. The intake/exhaust ratio is ground into the cam and cannot be changed by advancing or retarding the entire cam timing.

As a guide, if the rest of the numbers are comparable, a cam with a less separated lobe (e.g. 98 to 103 degrees) offers a wider spread of power and tends to produce bottom-end power, while the wide nubs cater for a more “cammy” camera that is used harder and later in the game. Lobe Separation Angles (LSA) of 100-103 degrees tend to produce performance on the low end.

LSA and lift affect the “sound” and idle quality. In general, smaller lobe separation angles cause an engine to produce more mid-range torque and higher rpm horsepower and responsiveness, while larger lobe separation angles result in broader torque, improved no-load characteristics, and more peak power.

A “tight” cam separation angle of 103 degrees or less creates more valve overlap, which helps create that lumpy idle characteristic of large cams. The tighter the LSAs, the more likely there will be problematic exhaust reversal into the intake. Put simply, we can say that a taut LSA cam produces a power curve that, for lack of a better description, is “punchy”. At low RPM off the cam, it runs rougher and comes out on the cam with more “bang”. Narrow LSAs tend to increase mid-range torque and result in faster revving engines. In general, smaller lobe separation angles cause an engine to produce more mid-range torque and power at high rpm and be more responsive. Typically, however, small center lobe numbers (more overlap) correspond to higher mid-range performance at the expense of high-end performance. Probably the most important factor for the engine tuner, however, is the tight LSA’s intolerance to exhaust system back pressure. Remember that during the overlap time both valves are open. If there is exhaust back pressure or if exhaust port velocities are too low, this will encourage exhaust gas reversal. A cam with a 102 degree cam separation angle has more overlap and a rougher idle than one with 108 degrees, but it usually puts out more midrange power. A narrower lobe has more overlap. A narrower centerline starts the torque curve earlier and doesn’t give a wide powerband. A wider cam doesn’t start the torque curve earlier, but makes the torque last longer and has a wider powerband.

Wide LSAs result in wider powerbands and more peak torque at the cost of a slightly lazier initial response. Larger cam separation angles result in wider torque, improved idle characteristics and more peak power. A wider cam doesn’t start the torque curve earlier, but makes the torque last longer and has a wider powerband. A street engine with a wide LSA will have higher vacuum and smoother idle. Big numbers (less overlap) give more top end and sacrifice midrange. A cam on wide centerlines creates a wider powerband. It will run smoother and produce better vacuum, but the price paid is a reduction in power throughout the working RPM range.

Narrow LSA (98-103)

Shifts the torque to a lower speed

Increase mid-range torque

Increases maximum torque

Fast turning motor and more responsive

Narrow powerband

Builds higher cylinder pressure

Increases the likelihood of engine knock

Increase cranking compression

Increase effective compression

Idle vacuum is reduced

Idle quality suffers (lumpy idle characteristics)

Open valve overlap increases

Closed valve overlap increases

Reduces the clearance between the piston and the valve

Wide LSA (104-108)

Increase the torque to a higher RPM

Reduces the maximum torque

Expands the powerband

Lazy initial reaction

More peak performance

Reduce the maximum cylinder pressure

Reduce the likelihood of engine knock

Decrease cranking compression

Decrease the effective compression

Idle vacuum is increased

Idle quality improves

Open valve overlap decreases

The overlap of closed valves decreases

Increases clearance between piston and valve

Overlap: The aim of the overlap is that the exhaust gas, which is already running down the tailpipe, acts like a siphon and draws fresh mixture into the combustion chamber. Otherwise, a small amount of burned gases would remain in the combustion chamber and dilute the incoming mixture on the intake stroke. Duration, lift and LSA combine to form an “overlap triangle”. The greater the duration and lift, the more overlap area, LSA remains the same. Given equal duration, LSA and overlap are inversely proportional: increased LSA decreases overlap (and vice versa). More overlap reduces vacuum and low-rpm response, but in the mid-range, the overlap improves the signal delivered from the fast-moving exhaust to the incoming intake charge. This increased signal typically provides a noticeable improvement in engine acceleration.

Less overlap increases efficiency by reducing the amount of raw fuel escaping through the exhaust, while improving low-end response as less exhaust flows back into the intake port; The result is better idling, a stronger vacuum signal and improved fuel economy. Due to differences in cylinder head, intake and exhaust configuration, different engine combinations are extremely sensitive to camshaft overlap area. Not only is the duration and area of ​​overlap important, but so is its overall shape. Many recent advances in cam design have come from carefully tailoring the shape of the overlap triangle. According to Comp Cams, some of the most critical engine factors for optimizing overlap include intake system efficiency, exhaust system efficiency, and how well the heads flow from intake to exhaust when both valves are slightly open.

A camshaft overlap duration of less than 30 degrees tends to produce good low-end power.

The overlap is the time that both the intake and exhaust valves are open. When done correctly, the overlap helps draw in the intake charge, but excessive amounts actually reduce performance by allowing the intake charge to escape out the open exhaust valve. Lots of overlap practically guarantees that a cam won’t perform well at low rpm, no matter how wide open it is. A camshaft overlap duration of less than 30 degrees tends to produce good low-end power.

Increased overlap equates to reduced idle quality, less vacuum, and harder running before hitting the cam. Lots of overlap works great at high rpm as more intake charge can cram into the cylinder, but lots of overlap also makes the engine run poorly at low rpm as the exhaust manages to make its way back up the intake manifold and gets diluted the incoming air/fuel charge and the deposition of soot on the intake ports, carburetor, etc. Cams with a lot of overlap tend to cause a rougher idle due to the lack of vacuum they create in the manifold.

The overlap (long duration and tight lobe separation angles) reduces cylinder pressure, especially at low rpm, which allows an engine to run at a higher compression ratio and still operate on pump gas. Ein hoher Zylinderdruck, der teilweise durch ein hohes Verdichtungsverhältnis verursacht wird, lässt einen Motor mit Pumpgas explodieren. Das Verringern des Zylinderdrucks durch Verlängerung der Dauer ist wie das Herausnehmen der Kompression aus dem Motor, aber meistens nur bei niedrigen Drehzahlen.

Dauer: Die Dauer hat einen deutlichen Einfluss auf das Leistungsband und die Fahrfähigkeit einer Kamera. Höhere Dauern erhöhen das obere Ende auf Kosten des unteren Endes. Die „beworbene Dauer“ einer Kamera war ein beliebtes Verkaufsinstrument, aber zwei verschiedene Kameras anhand dieser Zahlen zu vergleichen, ist heikel, da es keinen festgelegten Stößelanstieg zum Messen der beworbenen Dauer gibt. Die Messdauer bei 0,053 Zoll Stößelhub ist bei den meisten Hochleistungsnocken zum Standard geworden. Die meisten Motorenbauer sind der Meinung, dass die Dauer von 0,053 Zoll eng mit dem Drehzahlbereich zusammenhängt, in dem der Motor seine beste Leistung bringt. Wenn beim Vergleich zweier Nocken beide Profile die beworbene Dauer mit dem gleichen Anstieg bewerten, hat die Nocke mit der kürzeren beworbenen Dauer im Vergleich zu der Dauer von 0,053 Zoll eine aggressivere Rampe. Unter der Voraussetzung, dass eine stabile Ventilbewegung aufrechterhalten wird, führt das aggressive Profil zu einem besseren Vakuum, einem erhöhten Ansprechverhalten, einem breiteren Drehmomentbereich und Verbesserungen des Fahrverhaltens, da es effektiv die Öffnungs- und Schließpunkte eines kleineren Nockens in Kombination mit der Fläche unter der Hubkurve eines größeren Nockens aufweist . Motoren mit erheblichen Luftstrom- oder Kompressionsbeschränkungen wie aggressive Profile. Dies ist auf das erhöhte Signal zurückzuführen, das durch die Drosselung mehr Ladung erhält, und/oder auf die verringerte Sitzeinstellung, die zu einem früheren Schließen des Einlasses und mehr Zylinderdruck führt. Große Nocken mit längerer Dauer und Überlappung ermöglichen es Motoren mit begrenzter Oktanzahl, eine höhere Kompression zu betreiben, ohne im niedrigen bis mittleren Bereich zu detonieren. Umgekehrt führt eine zu große Nocke mit einem zu niedrigen Kompressionsverhältnis zu einer trägen Reaktion unter 3.000 U / min. Befolgen Sie die Empfehlungen der Nockenschleifer zur richtigen Anpassung des Nockenprofils an das Kompressionsverhältnis.

Die Dauer reicht im Allgemeinen von 220 Grad für einen drehmomentstarken Nocken am unteren Ende bis hin zu 295 Grad für einen „Ansturm am oberen Ende“, der typischerweise bei 0,053 Zoll Hub gemessen wird.

Als allgemeine Regel gilt, dass Nocken mit geringerer Dauer in der Nähe von 210 bis 200 Grad bei 0,053 am besten für Ersatznocken vom Originaltyp geeignet sind. Das Überschreiten von 220 Grad Dauer (bei 0,053) platziert die Nocke in der Kategorie des Bolt-On-Stils im mittleren Bereich. Diese Nocken funktionieren gut mit der serienmäßigen Kompression, dem Einlass und dem Auslass. Nocken mit mehr als 240 Grad Dauer oder mehr treten allmählich in die Leistungsarena ein und funktionieren im Allgemeinen besser mit anderen Ansaug-, Kompressions- und Abgasmodifikationen. Die Dauer hat einen deutlichen Einfluss auf das Leistungsband der Nockenwelle und das Fahrverhalten.

Höhere Dauern erhöhen das obere Ende auf Kosten des unteren Endes. Als allgemeine Regel gilt, dass Nocken mit einer Dauer von 220–235 Grad dazu neigen, ein gutes Drehmoment im unteren Bereich zu erzeugen. Nocken mit einer Dauer von 235-250 Grad funktionieren in der Regel am besten im mittleren Bereich und Nocken über 260 Grad funktionieren am besten für die Spitzenleistung.

Hierbei ist zu beachten, dass die angegebenen Dauerwerte als allgemeine Regel zu verwenden sind und dass eine Erhöhung der Dauer Auswirkungen auf das Leerlaufverhalten und das Gesamtfahrverhalten hat.

Nockenkonstruktionen mit langer Dauer und spätem Einlassschluss sind erforderlich, um das letzte bisschen Leistung aus einem Motor zu ziehen. Leider können dieselben Nocken unter normaleren Fahrbedingungen schlecht funktionieren. Auf der Suche nach maximaler Leistung wählen viel zu viele Harley-Besitzer eine spät schließende Nockenwelle mit hoher Drehzahl für ihren Motor. Das Problem bei solchen Entscheidungen ist, dass der Motor selten Zeit in dem Drehzahlbereich verbringt, der von solchen Nocken bevorzugt wird.

Hub: Eine weitere Methode zur Verbesserung der Nockenleistung ist die Erhöhung des Nockenhubs. Das Entwerfen eines Nockenprofils mit mehr Nockenhub führt zu einer längeren Dauer in den Bereichen mit hohem Hub, in denen die Zylinderköpfe am meisten Luft strömen. Nocken mit kurzer Dauer und relativ hohem Hub können ein hervorragendes Ansprechverhalten, ein großes Drehmoment und eine gute Leistung bieten. Nocken mit hohem Hub sind jedoch weniger zuverlässig. Sie benötigen die richtigen Ventilfedern, um den erhöhten Hub zu bewältigen, und die Köpfe müssen so eingestellt werden, dass sie den zusätzlichen Hub aufnehmen können. Es gibt einige Beispiele, bei denen ein erhöhter Auftrieb die Leistung aufgrund einer verringerten Geschwindigkeit durch den Hafen nicht verbessert. diese treten typischerweise in der Welt der Rennmotoren auf (0,650 bis 1,00 Zoll Ventilhub). Einige neuere Motorenmodelle mit restriktivem Drosselklappengehäuse, Einlass, Zylinderkopflauf und Abgasstrom können einfach nicht genug Luft strömen lassen, um einen höheren Auftrieb zu unterstützen.

Der Nocken- (oder Nocken-) Hub ist die maximale Höhe oder Entfernung, um die der Heber oder Mitnehmer von der Nocke angehoben wird. Mehr Auftrieb bedeutet im Allgemeinen eine bessere Leistung am oberen Ende, aber Sie werden die Reaktion am unteren Ende opfern. Außerdem belasten Nocken mit hohem Hub den Ventiltrieb stärker.

Bei Straßenrädern werden die Hubzahlen am besten bei oder unter 0,500 Zoll gehalten, einfach weil Sie mit der richtigen Nocke immer noch die gesamte Leistung abrufen können, die Sie verwenden können, aber Sie benötigen nicht alle 20.000 Meilen einen neuen Ventiltrieb. Sicher, mit der richtigen Zylinderkopf/Kolben-Kombination können Anhebungen im mittleren 0,500-Zoll-Bereich funktionieren, sogar ein Übergreifen auf 0,600 Zoll kann funktionieren, aber Stößelstangen biegen sich, die Geometrie geht AWOL, und die zusätzlichen Vorteile des Auftriebs werden durch die Grenzen des Durchflusses zunichte gemacht durch die Öffnungen (insbesondere die Auslassöffnung), also warum sich die Mühe machen? Mega-Lift ist wertvoller für Drag Racer, die die gesamte Handlung sowieso umgestalten.

Das andere potenzielle Problem bei der Erhöhung des Nockenhubs besteht darin, dass zwischen dem Kolben und dem Ventil nur ein begrenztes Spiel vorhanden ist. Das andere Problem im Zusammenhang mit erhöhten Hubzahlen ist die Frühjahrsermüdung. Je größer der Hub, desto weiter muss sich die Feder bei jeder Drehung des Nockens ausdehnen und zusammenziehen. Nocken mit mehr Hub belasten die Federn viel stärker, was zu einer Verringerung der Federlebensdauer führt.

Symmetrical cams: This simply means that the cam lobe is the same on both sides. This means that the valve opens and closes at the same rate.

Asymmetric Lobes: In the past, both opening and closing sides of a cam lobe were identical. Most recently, designers developed asymmetrical lobes, wherein the shape of the opening and closing sides differ. Asymmetry helps optimize the dynamics of a valve train system by producing a lobe with the shortest seat timing and the most area. The designer wants to open the valve as fast as possible without overcoming the spring’s ability to absorb the valve train’s kinetic energy, then close the valve as fast as possible without resulting in valve bounce. There are many different theories about how to design the most aggressive, stable profile. Hydraulic lifters can provide quiet valve train operation only if the closing velocity is kept below a certain threshold. However, the opening velocity can be higher and still provide quiet operation. Almost all modern hydraulic profiles have some symmetry.

Here the lobes differ from the opening side to the closing side. This allows the cam grinder to open the valve a one speed and close it at another. Here is where some cams are quite and some noisy. If the grinder has chosen to set the valve down slowly on the seat it will be a quitter cam than if the grind lets the valve down too quickly. Single pattern cams In the case of single pattern cams both the intake and exhaust lobe are the same. A cam can be asymmetrical and single pattern or symmetrical and single pattern. Dual pattern cams have different profiles on the intake and exhaust lobes. A cam of this type can be any combination of asymmetrical or symmetrical of profiles.

Camshaft Noise: Camshaft noise is partly from cam shaft ramp design and partly mechanical noise from end play and excess gear lash. Camshaft noise and gear lash is dictated by the cam support plate. When the teeth of the gears mesh, they produce annoying whine if they mesh too tightly and a clackety clatter if they’re too loose. However, these gears also expand slightly when the engine is at operating temperature and then return to their original size when the engine cools down, which is why it’s impossible to get them to be quiet all the time.. Throw in loose manufacturing tolerances on the cam support plate and you have a complicated issue on your hands, which is why Harley replaced gear driven cams with chain driven cams.

Effect of Compression Ratio on Camshaft Selection: It is instructive to remember that the static compression ratio that your engine displays on paper does not translate directly to higher cylinder pressures. The cylinder pressure (prior to ignition) during engine operation is dependent on what can loosely be called “dynamic or effective compression ratio”. The pressure is greatly affected by the timing of your valve events – i.e. cam duration and timing. Specifically, the intake valve closing point is intimately related to an engine’s dynamic, or “effective” compression ratio.

But we just learned on static compression ratio is directly related to stroke. In principle, the piston cannot compress the mixture until the intake valve closes. Thus if the intake valve closes when the piston has already moved quite some distance up the bore, then the amount that the intake charge will be compressed is reduced. The “effective compression stroke” has been reduced. Does this mean that when an engine is operating that the dynamic compression ratio is lower than the static compression ratio? Well yes and no.

An engine with a performance cam operating at low RPM will suffer a loss of torque due to the fact that the effective compression ratio is reduced by the late intake valve closing point. However, as the RPM increases “inertia supercharging” becomes important. At high RPM’s the intake charge is is moving into the cylinder at high velocity. As such it has a lot of inertia and will continue moving into the cylinder past BDC, even though the piston has changed direction and is now moving up the bore (towards the incoming charge). Ideally the intake valve will close just before the incoming air stops and reverses direction. This guarantees that the maximum amount of air/fuel mixture has been drawn into the cylinder prior to ignition. When this happens an engine is said to have “come on the cam”. In order to ensure that the mixture is still compressed sufficiently over the reduced effective compression stroke it is necessary to increase the static compression ratio. This is why high performance engines with aggressive camshafts also tend to have high static compression ratios.

Bottom line: Static compression ratio and cam choice should be considered as a system.

A mild cam with an early intake valve closing point will work well at low RPM. But at high RPM the intake valve will close before the maximum amount of air/fuel mixture has been drawn into the cylinder. As a result performance at high RPM will suffer. If a high static compression ratio is used with a mild cam (i.e. and early intake valve closing point) then the mixture may end up being “over-compressed”. This will lead to excessive compression losses, detonation and could even lead to head gasket or piston failure.

On the other hand, an aggressive cam with a late intake valve closing point will work well at high RPM. But at low RPM the intake valve will close too late for sufficient compression of the intake charge to occur. As a result torque and performance will suffer. If a low static compression ratio is used with an aggressive cam (i.e. a late intake valve closing point) then the mixture may end up being “under-compressed”. Thus a high performance cam with long duration should ideally be combined with a higher static compression ratio. That way the engine can benefit at high RPM from the maximized amount of intake charge afforded by the late intake valve closing, and still achieve sufficient compression of the mixture as a by-product of the dynamic compression ratio.

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Being able to drive a cam every day has a lot to do with the cam profile and tune – also whether it’s a car or not. For example, if you have a cam that doesn’t play well with the stock torque converter, you can experience judder and judder, which isn’t fun in everyday driving. Smaller cams tend to be a bit more forgiving and offer a more stock riding experience.

With a manual car, however, you have a lot more leeway. It all comes down to the tune and how well you can operate your clutch. For years I drove a car with a cam shift transmission every day – in traffic. I loved every second of it and would love to do it again. As long as all of your hardware works and nothing is too aggressive, you should be able to use it on a daily basis without any problems. Just make sure you set aside some cash to replace the valve springs depending on how many miles you plan to put on each year.

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2018 Audi TT▊RS

Engine built by RSP. H-Performance TC800XT. D S 1 flex fuel tune by Darin. Uni Stage 4 TCU, 800+Whp

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One of the most important components in any engine is the camshaft. Whether in a push rod engine or an overhead cam engine, the camshaft controls the opening and closing of the valves. This in turn controls the flow of air and fuel in and out of the engine, which determines engine performance, fuel economy and emissions.

In pushrod engines, the camshaft is driven by the crankshaft either via a chain or a gear. In OHC engines, the camshaft can be belt or chain driven from the crankshaft or an intermediate shaft. The drive ratio is always 1:2, so the cam rotates at half the crankshaft speed. This is because the crankshaft makes two complete revolutions for each power stroke (intake, compression, power, and exhaust) in a four-stroke engine.

Cam-related issues can occur due to a variety of reasons. As an engine accumulates miles, the timing chain stretches. The extra slack in the chain has a retarding effect on cam timing, reducing compression and torque. It can also retard ignition timing if the distributor is cam driven. Most OHC engines that use a chain drive have some sort of automatic chain tensioner, but pushrod engines do not. As a result, the timing chain and gear set often need to be replaced in pushrod engines with high mileage.

For OHC engines with belt driven cams, the main problem is belt breakage. If the belt breaks, the cam will stop rotating and the engine will stall. Some valves are held in the open position, which can result in bent valves and/or damaged pistons if the engine does not have enough clearance between the pistons and valves to run freely.

To minimize the risk of such damage, most vehicle manufacturers recommend replacing OHC timing belts at certain mileage intervals for preventive maintenance. For older OHC engines, the typical replacement interval is 60,000 miles. For newer OHC engines it is 100,000 miles.

Lubrication problems in the engine can lead to cam failure. Lifters create a lot of pressure and friction on the cams, so the cams and cam bearings need to get a lot of oil. If the oil pressure is low or the oil is dirty, accelerated cam wear and eventual cam failure can result, resulting in a dead cylinder (no valve action).

This type of cam damage can also be caused by using an incorrect viscosity engine oil. On overhead cam engines, it’s a long way from the oil pump to the top of the cylinder head. On cold mornings when the oil is thick it can take a few seconds for sufficient oil pressure to reach the cam. For this reason, most vehicle manufacturers recommend using 5W-30 oil instead of 10W-30 or 10W-40 for cold weather driving.

Cam breakage or seizing is another problem that can occur with OHC engines. The cause can be insufficient lubrication, but in many cases it is caused by head deformation.

When an OHC engine overheats, the cylinder head tends to swell and bulge in the middle. This changes the alignment of the cam bores in the head, which can cause the cam to bend, bind, seize, or break. If an overhead cam does not rotate freely in the head when the belt and cam followers are removed, then either the cam is bent or the head is warped and needs to be straightened and/or bored out.

AFTERMARKET PERFORMANCE CAMSHAFTS

Camshafts are often replaced to increase engine power and performance. But choosing a high-performance aftermarket camera isn’t as easy as it sounds. In order to find the “right” replacement camera, a few things have to be considered. This includes not only the engine and vehicle application, but also the compression ratio of the engine, the type of fuel supply system, other modifications (intake and exhaust manifold, exhaust system, etc.), cylinder heads, transmissions and differentials, and even the size of the tires.

But most importantly, what exactly do you want from an aftermarket performance replacement cam? More force? More torque to tow? Better mileage?

CHOOSING THE “RIGHT” CAMSHAFT PROFILE

If you look through the catalogs of the various performance cam manufacturers, you will notice two things. The first is that there are many, many different nock grinds to choose from. The more popular the engine application (e.g. small block Chevy), the greater the variety of cams offered. The other thing is that there are specific recommendations for each type of camera. So the best advice here is to follow the camshaft supplier’s advice.

A typical replacement cam (either a new cam or a reground cam) is essentially a duplicate of the OEM grind. This type of cam is used to restore the engine’s original performance and is a safe bet for a stock rebuild.

The next step is the cams with slightly “extended” profiles. These include the mileage/economy cams, tow cams, and mild performance cams. Idling quality, drivability and emissions remain about the same as the original, but the engine is more powerful and slightly more fuel efficient.

Once you move beyond the standard replacement cams, the selection process becomes more complicated as each grind is designed for a specific type of application. Vehicle weight, drive ratios and type of transmission (automatic versus manual) are gaining in importance, as are modifications to the engine itself (compression, displacement, mixture formation, valve size, valve train, etc.).

The most common mistake to avoid when selecting a camshaft is to “overdrive” an engine. Installing a hot cam in an otherwise stock engine can result in a poor mismatch between components, and that hurts performance rather than performance. A cam with long duration and a rough idle may sound very hot, but it may not offer as much low-end punch as a stock cam. Emissions can also be a problem with long-term cameras.

COMPARISON OF CAMSHAFT PERFORMANCE SPECIFICATIONS

When comparing cameras you will find a number of specifications listed. These include lift, duration, overlap, lobe separation, and timing.

The valve lift indicates how far the cam opens the valves. Increasing valve lift increases valve opening travel, allowing more air and fuel to enter the cylinders more easily. An increase in airflow is achieved by increasing lift to the point where either the area of ​​the valve orifice or port becomes the limiting factor for airflow, or there is mechanical interference between the valve and piston, valve springs or spring retainer and valve guide.

One way to specify valve lift is to measure “cam lift”. That’s how far the cam actually moves the lifter, that’s the maximum height of the cam above its base circle. But the valve doesn’t really open that far. To get that number, you need to factor in the rocker arm ratio minus the valve clearance. “Gross lift”, the number most often quoted in catalogues, is cam lift multiplied by rocker arm ratio. The gross lift gives you the theoretical valve lift of the cam. “Net lift” is how far the valve actually opens when you subtract the valve lash in the valve train.

Duration is how long the cam keeps the valves open and is measured in degrees of crankshaft rotation. From here, the definition of duration becomes fuzzy, as it can be measured and advertised in a variety of ways.

Duration depends on how and where it is measured. When the cam reverses and a cam begins to push its lifter up, the valve begins to open, but not immediately. A few things happen first. The valve does not begin to open until all play in the valve train has been used up. The cam nose also gradually rises from the base circle, making it difficult to measure the exact point where the lifter starts to move.

One way to measure duration is to start when the lifter has risen 0.004 inches above the base circle of the cam. The degrees of crankshaft rotation are then counted until the tappet comes back down to within 0.004 inch of the base circle. This method is often referred to as “advertised duration”. They call it that because the duration numbers it generates are much larger (and sometimes misleading) than those generated by the following techniques.

The Society of Automotive Engineers (SAE) states that duration is to be measured at 0.006 inches above base circle for hydraulic cams and 0.006 inches plus specified valve clearance for mechanical solid tappet cams.

The other common method of specifying duration is to measure it 0.050 inches above the base circle. The .050″ specs are the most commonly cited in aftermarket catalogs and are the ones we will use when discussing specific recommendations for the long run.

What does a lifetime specification tell you about a camshaft? It shows you the potential of the camshaft to produce power in a given RPM range. Generally speaking, the longer the duration, the higher the operating range of the cam. Short duration cams are good for low speed torque and throttle response, while long duration cams keep the valves open longer to breathe better at high speed.

Camshafts up to 220 degrees duration (at 0.050 in cam lift) are considered best for unmodified stock engines and those with computerized engine management. Once you exceed 220 degrees of duration, intake vacuum begins to drop noticeably, disrupting idle quality and affecting the operation of computerized engine control systems.

Some information about the duration says nothing about the club profile. Two different camshafts can have identical lift and duration specifications, but the lobes on one cam can be ground differently than on the other. One camshaft may have a more spiky lobe while the other has a “fatter” lobe. A “V” shaped lobe breathes differently than a “U” shaped lobe because it does not hold the valve at its maximum opening for as long. Valve float can also be a problem with cams that change shape abruptly unless valve spring pressure is increased. The profile of the lobes on a camshaft can also be the same on the top and bottom of the lobe (which is the norm for most stock and street performance lobes) versus an “asymmetrical” grind (different profiles on each side of lobes). the other cam.

Another specification to look for when choosing a cam is the relative timing of the intake and exhaust valves. This can be expressed as either “valve overlap” (the time during which both the intake and exhaust valves are open) or “cam separation” (the number of degrees or angle between the centerlines of the intake and exhaust cams). Decreasing the beam spacing increases the overlap, while increasing the spacing decreases the overlap.

Most stock replacement cams less than 200 degrees in duration have cam spacing of 112 to 114 degrees. Longer duration cams for mid-range performance typically have 110 to 112 degrees of lobe separation. On racing cameras you will find beam separations between 106 and 108 degrees.

Overlap occurs when the intake valve begins to open before the exhaust valve has finished closing. Increasing the overlap can be desirable in higher RPM applications as the exiting exhaust gas is actually helping to scavenge the cylinder to draw more air and fuel into the combustion chamber. But too much overlap at low rpm kills low-end torque and throttle response by unduly reducing intake vacuum. It can also cause idle emissions problems by allowing unburned fuel to be sucked into the exhaust.

Some OE cams use a little more overlap to create an exhaust gas recirculation (EGR) effect to reduce NOX (nitrogen oxides) emissions. The trade-off is usually some throttle response and bottom-end torque. Replacing this type of cam with a cam with less overlap (greater lobe spacing) can significantly improve performance.

Performance camshaft with friction-reducing roller lifters.

FLAT TAPPET OR ROLLER CAM?

A roller cam uses lifters that have small anti-friction rollers on the bottom. Roller cams are used on stock engines to reduce friction. Roller cams are used in high performance engines to offer more radical cam profiles. The rollers on the underside of the lifters can roll up and over a steeper incline than a flat follower cam.

Flat tappet cams were used in most engines until the mid-1980s, when vehicle manufacturers began to switch to roller cams. The valve lifters, which ride on a flat lifter cam, are actually slightly convex on the underside. The curvature combined with a slight slope on the cam itself causes the lifter to rotate as it rides up and down. This is done to reduce friction and wear.

Which one is better? Depends on what engine you are building. If you are building a high RPM engine, a flat cam follower with solid tappets will deliver most RPM without valve floats. However, solid jacks are noisy and require regular adjustments. In comparison, a camshaft with hydraulic tappets is a good choice for a street engine or a lower-rpm engine designed for a lot of torque.

CAMSHAFT TIMING AND INSTALLATION

Cam timing is the advance or retard between the cam and the crankshaft. Cam timing can be verified by comparing cam spread and intake cam center using a degree wheel and dial indicator.

A common mistake is assuming that cam timing is correct as long as the timing marks on the cam gear are properly aligned. That might be a safe assumption on a stock cam, but it’s not good enough for a high-performance engine rebuild. The cam can be advanced or retarded depending on the alignment of the cam gear (crankshaft gear and cam gear), the amount of wear or play in the cam gear (gear play, belt wear or chain stretch), and the geometry of the cam gear. Refacing an OHC cylinder head can also alter the cam timing, potentially requiring the installation of a thicker head gasket and/or offsetting the cam drive pulley to compensate.

Why is cam timing so important? Because it affects engine performance. In order for the engine to run optimally, it needs precise cam timing. Typically, advancing the cam timing by 2 to 4 degrees helps with low RPM torque and throttle response with little sacrifice in higher RPM power. Advancing the cam also helps compensate for chain stretch as the engine ages. Retarding the cam, on the other hand, can improve high-rpm power, but usually at the expense of low-rpm torque. A retarded cam is something you don’t want in a stock or street performance engine.

Another thing to note is that many aftermarket cams are not ground “straight up” with zero timing offset. Many already have about four degrees of advance built into the cam to accommodate timing chain stretch as the engine ages.

If the camshaft timing is not measured with a degree wheel and someone installs an offset dowel pin or cam drive gear to advance the cam timing an additional four degrees, it can result in too much advance and potentially valve-to-piston interference issues.

Finally, anyone replacing a camshaft with flat bottom lifters should replace the cam and lifter at the same time.

Worn lifters can damage a new cam. New valve springs should also be recommended.

Cams should always be protected with assembly lubricant when installing a cam. For cams with flat tappets, apply a high pressure molybdenum based grease to all cams all around. Use engine oil or red assembly oil on the camshaft journals. For roller cams, use engine oil or red assembly lube on the cams and trunnions. DO NOT use molybdenum paste lubricant on the lobes of a roller camshaft.

Flat tappet cams should be broken in using the manufacturer’s recommended procedure (typically running at 2,000 rpm for up to 30 minutes when the engine is first started). Roller cams should not require special break-in. Nevertheless, the engine should run at fast idle for some time in order to spray lubricate the piston rings when they are inserted.

The cams on this 289 Ford Mustang flat tappet cam suffered from excessive wear due to insufficient levels of ZDDP anti-wear additive in the engine oil.

CAM WEAR PROBLEMS WITH FLAT TAPPET WITH LOW ZINC ENGINE OILS

If you drive an older classic muscle car or hot rod that has a flat tappet cam engine, you should be aware of the fact that today’s “SM” rated engine oils have a lot less called anti-scuff additive “ZDDP” included. (Zinc dialkyldithiophosphate). The level of ZDDP in current engine oils has been reduced to no more than 0.08% phosphorus to extend catalyst life. Phosphorus can foul the catalytic converter over time when the engine uses oil, leading to increases in tailpipe emissions.

The lower ZDDP level is not detrimental to newer engine models with roller lifters or followers since the loads on the camshaft lobes are much lower. However, in pushrod engines with flat cam followers, the ZDDP value may be insufficient to prevent cam and follower wear. In some cases, cam failures have occurred after only a few thousand miles of driving! This is an even greater risk on engines using stiffer valve springs and/or higher lift rocker arms.

To avoid such problems, you should add a ZDDP additive to the crankcase or use an oil that meets the previous “SL” rating, or use diesel engine oil or racing oil that contains sufficient amounts of ZDDP to seal the camshaft and tappets protection.

When installing a new camshaft on the engine, be sure to use the camshaft supplier’s moly cam paste on the cam lobes (use oil or red assembly lube on the journals) and follow the recommended break-in procedure. However, you still need to add ZDDP to the crankcase or use an oil that contains a reasonable level of ZDDP to ensure lasting protection.

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The camshaft is crucial for the basic function of an engine. Composed of two distinct parts, the cams and the shaft, the camshaft is the element that allows the valves to open. As the shaft rotates, the egg-shaped cams (or “cams”) force the valves open in synchronism with the crankshaft gear.

Identifying the camshaft A collection of camshafts from car and truck engines. ThyssenKrupp Presta Chemnitz GmbH / Wikimedia Commons In modern overhead cam (OHC) engines, the camshaft is located in the cylinder head. Single OHC (SOHC) engines have one cam per bank, usually mounted between the valve stems. Rocker arms transmit the SOHC movement to the valves. Dual OHC (DOHC) engines have two cams per bank, usually directly above the valve stems, one for intake valves and one for exhaust valves. The force is transmitted directly to the valve. An i4 SOHC (four-cylinder) engine has one camshaft, while a V6 or V8 SOHC engine has two. An i4 DOHC engine has two camshafts, while a V6 or V8 DOHC engine has four camshafts. Overhead camshaft engines have three to five valves per cylinder, but usually two intake valves and two exhaust valves. Older engines and some newer “pushrod” engines have a single camshaft in the cylinder block. Long metal pushrods transmit camshaft motion to the rocker arms, which transmit that motion to the valves. Pushrod engines usually have two or three valves per cylinder, usually one intake valve and one exhaust valve. The typical camshaft is milled from a preformed cast steel blank. Some performance and custom cams can be machined from a solid block of steel.

How camshafts work vladru/Getty Images As the camshaft rotates, the lobes move up and down. On DOHC engines, each rotation causes a single cam to push the valve down and open it into the cylinder. Similarly, on SOHC and pushrod engines, the cam pushes on the rocker arms (or pushrods then rocker arms) and opens the valve. As the cam continues to turn, the valve spring pushes the valve back up and closes it. The camshaft is usually connected to the crankshaft via a timing chain or timing belt. Timing gears may also be used on some pushrod engines. The camshaft sprocket has twice as many teeth as the crankshaft sprocket, which allows it to turn at half the speed of the crankshaft. The camshaft has four different lifts: intake, compression, power and exhaust. Conventional camshafts are manufactured to match typical operating characteristics and may emphasize efficiency when driving on freeways or low-end performance. Similarly, valve “lift” refers to the height of the lobe in relation to the center of the shaft, which determines how far the valve opens. With fixed cams this is not adjustable, but there are circumstances where the engine could ‘breathe’ better if only the valves could open a little more. Also, a fixed camshaft could open the intake valve 10° before TDC (BTDC) and close 5° after bottom dead center (ABDC) and open the exhaust valve 15° before bottom dead center (BBDC) and close 5° ATDC. This is called the valve open duration. This works well on average, but does not shine in any driving situation.

Special camshaft functions These hydraulic camshaft adjusters cause variable valve timing on the intake and exhaust valves. DmitryKo/Wikimedia Commons Timing is important. Valves must open and close at specific intervals in relation to cylinder position. For example, when cylinder #1 comes to top dead center (TDC) on the exhaust stroke, the camshaft opens the intake valves and closes the exhaust valves. At the same time, cylinder #3 could reach top dead center on the compression stroke, so the camshaft would leave those valves closed. Camshafts equipped with variable valve timing (VVT) use hydraulic actuators to advance or retard valve timing in relation to crankshaft angle. VVT allows for high speed efficiency or low speed performance. Using dedicated variable valve lift (VVL) camshafts and computer controlled solenoids or hydraulic actuators, the ECM can select between two valve lift options depending on driver preference. On direct injection vehicles, some diesel engines and most direct injection gasoline engines, the high pressure fuel pump (HPFP) is driven by a cam on one of the camshafts.