Explaining How Cams Work and What the Numbers Mean, Parts 1 & 2
Engine Mechanical TopicsDiscussion for motor builds, cams, head work, stripped bolts and other engine related issues. The good and the bad. If it goes round and around or up and down, post it here.
It's amazing someone would take the time to post such a comprehensive description, thank you for your efforts. I'm not gonna lie though, with my overall limited mechanical understanding its a lot to absorb. So I might just pose a question and hope to draw on some wiser experience.
I am awaiting delivery of a 2014 CVO Breakout. I want to plan the motor mods before hand, and have heard nothing but good things about Woods cams. I would like to put a S/E stage 3 or 4 kit through it, but substitute the Harley cams for Woods cams. The bike would be mainly used for shorter rides with frequent periods of fun with mates trying to keep up haha. Is this a sensible fit and what would be the appropriate cams to use?
I have a 14 Breakout, 103" motor, K&N intake/filter, and have been building/playing with the internals of the stock mufflers. Basically, it's a glass pack right now, w/ out the cats. Power Vision is in the mail. Been reading a lot on cams lately. My riding right now is mainly highway and town. Usually in the 2000-3200 RPM range. Looking for something that will give more snap in these areas, but will be dependable on longer rides. Usually put on 100-150 miles a night after work, just joy riding. Not looking for a drag racer, but better performance in the low-mid cruising areas. Any speculation on a cam & it's TQ/HP numbers for this setup?
Just Had it done on my 13 Ultra.
Screamin eagle street cannon exhaust
Screamin Eagle high flow air cleaner
Super Tuner Pro
10.5:1 Pistons
259E Cam
Heavier clutch
Ported heads
58mm Throttle body
I really like the results For me it pulls much harder in the 15-2500 rpm range and also pulls steady up into 4-4500 range. I do notice the engine has more top end noise than before. I was told by the dealer this is due to the heavier valve springs. I would recommend this build to anyone who wants good low end performance as well as the ability to downshift a gear and pass vehicle with ease. Don't have any dyne numbers, but there is a huge difference over stock.
Explaining How Cams Work and What the Numbers Mean, Part 2
Lobe Centerline: Lobe 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 intake centerline from 98 to 108 degrees. An intake centerline of 98 is considered to be the most advanced and generally gives the most torque. A centerline of 108 will give power in the upper RPM range.
An exhaust centerline of 112 is the most advanced while the 102 is the most retarded. Again an advanced lobe will give power in the lower RPM range while the retarded lobe will have it's power range extended in the RPM range. For practical terms, most cams for Harley are in the range of 96-108 on intake and 112-102 on the exhaust.
Tailoring the valve opening and closing points on an actual camshaft is accomplished by varying the lobe centerline locations, changing the LSA, and refining the profile shape itself. Advancing the cam moves both the intake and exhaust in an equal amount, resulting in earlier valve timing events. Engines typically respond better with a few degrees of advance, probably due to the importance of the intake closing point on performance. For racing, advanced cams benefit torque converter stall, improve off-the-line drag race launches, and help circle-track cars come off the corner. Cam companies often grind their street cams advanced (4 degrees is typical), which allows the end-user to receive the benefits of increased cylinder pressure yet still install the cam using the standard timing marks. Increasing the intake lobe centerline from 104 to 106 degrees is considered retarding. All events will take place later in the engine cycle. Retarding the cam causes the intake valve to open and close later. This will reduce cylinder pressure which reduces the low speed performance of the engine.
Advancing the intake and retarding the exhaust (“closing up the centers”) increases overlap and should move the power up in the RPM range, usually at the sacrifice of bottom end power. The result would be lower numerical values on both intake and exhaust lobe centers.
Retarding the intake and advancing the exhaust (“spreading the centers”) decreases overlap and should result in a wider power band at the sacrifice of some top end power. This condition would be indicated by higher numerical values on both intake and exhaust lobe centers. By moving only one cam the results are less predictable, but usually it is the intake that is moved to change power characteristics since small changes here seem to have a greater effect.
Lobe Separation Angle: Lobe separation is the angle between the center bump of the intake lobe and its counterpart on the exhaust lobe. Think of it like the two points on a pair of scissors relative to the hinge in the middle. If the scissors are nearly closed, you can cut well as long as what you are cutting is thin. To cut thick stuff, you open wider, but have less leverage, so it can be harder to get the done. The same principle applies with separation on cam lobes. Typically, lobe separation for street cams runs between 97 and 108 (camshaft) degrees. The relationship between intake and exhaust is ground into the cam and can’t be altered by advancing or retarding the overall cam timing.
As a guideline, if the rest of the numbers are comparable, a cam with a lobe that is less separate (for example, 98 to 103 degrees) will offer a broader spread of power and tend to produce power at the low end, while wide lobes make for a more “cammy” cam, coming on harder and later in the game. Lobe Separation Angles (LSA) of 100-103 degrees tend to produce power at the low end.
LSA and Lift affect the "sound" and idle quality. Generally, smaller lobe separation angles cause an engine to produce more mid-range torque and high RPM power, and be more responsive, while larger lobe separation angles result in broader torque, improved idle characteristics, and more peak horsepower.
A “tight” lobe separation angle of 103 degrees or less creates more valve overlap, which helps create that lumpy idle characteristic of big camshafts. The tighter LSA’s are, the more likely problematical exhaust reversion into the intake will occur. Put simply, we can say that a tight LSA cam produces a power curve that is, for want of a better description, more "punchy." At low RPM when off the cam, it runs rougher, and it comes on the cam with more of a "bang." Narrow LSA’s tend to increase mid-range torque and result in faster revving engines. Generally, smaller lobe separation angles cause an engine to produce more mid-range torque and high RPM power, and be more responsive. Typically, however, small lobe center numbers (more overlap) equates to more mid-range power at the expense of top-end power. Probably the most significant factor to the engine tuner though is a tight LSA’s intolerance of exhaust system back-pressure. Remember, during the overlap period both valves are open. If there’s any exhaust back-pressure or if the exhaust port velocities are too low it will encourage exhaust reversion. A cam with 102 degrees of lobe separation angle will have more overlap and a rougher idle than one with 108 degrees, but it'll usually make more mid-range power. A tighter lobe has more overlap. A tighter centerline starts torque curve sooner, and doesn't give a wide power band. A wider lobe doesn't start the torque curve sooner, but it continues to make torque longer and has a broader power band.
Wide LSA’s result in wider power bands and more peak torque at the price of somewhat lazier initial response. Larger lobe separation angles result in broader torque, improved idle characteristics, and more peak horsepower. A wider lobe doesn't start the torque curve sooner, but it continues to make torque longer and has a broader power band. A street engine with a wide LSA has higher vacuum and a smoother idle. Big numbers (less overlap) will give more top end, sacrificing mid-range. A cam on wide centerlines produces a wider power band. It will idle smoother and produce better vacuum, but the price paid is a reduction in output throughout the working RPM range.
Narrow LSA (98-103)
Moves Torque to Lower RPM
Increase mid-range Torque
Increases Maximum Torque
Faster revving engine and more responsive
Narrow Power band
Builds Higher Cylinder Pressure
Increase Chance of Engine Knock
Increase Cranking Compression
Increase Effective Compression
Idle Vacuum is Reduced
Idle Quality Suffers (lumpy idle characteristic)
Open Valve-Overlap Increases
Closed Valve-Overlap Increases
Decreases Piston-to-Valve Clearance
Wide LSA (104-108)
Raise Torque to Higher RPM
Reduces Maximum Torque
Broadens Power Band
Lazier initial response
More peak Horsepower
Reduce Maximum Cylinder Pressure
Decrease Chance of Engine Knock
Decrease Cranking Compression
Decrease Effective Compression
Idle Vacuum is Increased
Idle Quality Improves
Open Valve-Overlap Decreases
Closed Valve-Overlap Decreases
Increases Piston-to-Valve Clearance
Overlap: The objective of overlap is for the exhaust gas which is already running down the exhaust pipe, to create an effect like a siphon and pull a fresh mixture into the combustion chamber. Otherwise, a small amount of burned gasses would remain in the combustion chamber and dilute the incoming mixture on the intake stroke. Duration, lift and LSA combine to produce an "overlap triangle". The greater the duration and lift, the more overlap area, LSA’s remaining equal. Given the same duration, LSA and overlap are inversely proportional: Increased LSA decreases overlap (and visa versa). More overlap decreases low RPM vacuum and response, but in the mid-range, overlap improves the signal provided by the fast moving exhaust to the incoming intake charge. This increased signal typically provides a noticeable engine acceleration improvement.
Less overlap increases efficiency by reducing the amount of raw fuel that escapes thru the exhaust, while improving low-end response due to less reversion of the exhaust gasses back up the intake port; the result is better idle, stronger vacuum signal and improved fuel economy. Due to the differences in cylinder head, intake and exhaust configuration, different engine combos are extremely sensitive to the camshaft’s overlap region. Not only is the duration and area of the overlap important but also its overall shape. Much recent progress in cam design has been due to careful tailoring of the shape of the overlap triangle. According to Comp Cams, the most critical engine factors for optimizing overlap include intake system efficiency, exhaust system efficiency, and how well the heads flow from the intake toward the exhaust with both valves slightly open.
Camshaft overlap duration less than 30 degrees tends to produce good low end power.
Overlap amounts to the time the intake and the exhaust valves are both open. When you get it right, overlap helps draw in the intake charge, but excessive amounts actually reduce power by letting intake charge escape out the open exhaust valve. Lots of overlap virtually guarantees a cam won’t work well at low RPM, regardless of how strong it is wide open. Camshaft overlap duration of less than 30 degrees tends to produce good low end power.
Increased overlap equates to reduced idle quality, vacuum, and harsher running prior to coming up on the cam. Lots of overlap works great at high RPM because more intake charge manages to cram itself into the cylinder, but lots of overlap will also make the engine run badly at low RPM, as exhaust gas manages to make its way back up the intake manifold, diluting the incoming air/fuel charge, and depositing soot on the intake runners, carburetor, etc. Cams with a lot of overlap tend to cause rougher idling because of the lack of vacuum they create in the manifold.
Overlap (lots of duration and tight lobe-separation angles) decreases cylinder pressure, especially at low RPM, which allows an engine to run a higher compression ratio and still work on pump gas. High cylinder pressure, which is caused partly by a high compression ratio, is what makes an engine detonate on pump gas. Decreasing the cylinder pressure by adding duration is just like taking compression out of the engine, but mostly only at low RPM.
Duration: Duration has a marked affect on a cam's power band and drive-ability. Higher durations increase the top-end at the expense of the low end. A cam's "advertised duration" has been a popular sales tool, but to compare two different cams using these numbers is dicey because there's no set tappet rise for measuring advertised duration. Measuring duration at 0.053-inch tappet lift has become standard with most high-performance cams. Most engine builders feel that 0.053” duration is closely related to the RPM range where the engine makes it's best power. When comparing two cams, if both profiles rate the advertised duration at the same lift, the cam with the shorter advertised duration in comparison to the 0.053” duration has a more aggressive ramp. Providing it maintains stable valve motion, the aggressive profile yields better vacuum, increased responsiveness, a broader torque range, and drivability improvements because it effectively has the opening and closing points of a smaller cam combined with the area under the lift curve of a larger cam. Engines with significant airflow or compression restrictions like aggressive profiles. This is due to the increased signal that gets more of the charge through the restriction and/or the decreased seat timing that results in earlier intake closing and more cylinder pressure. Big cams with more duration and overlap allow octane-limited engines to run higher compression without detonating in the low to mid-range. Conversely, running too big a cam, with too low a compression ratio leads to a sluggish response below 3,000 RPM. Follow the cam grinders recommendations on proper cam profile-to-compression ratio match-up.
Duration generally ranges from 220 degrees for a torquey bottom-end cam all the way to 295 degrees for a of “top end rush,” typically measured at 0.053 inch lift.
As a general rule, lower-duration cams in the neighborhood of 210 to 200 degrees at 0.053 work best for stock-type replacement cams. Stepping past 220 degrees of duration (at 0.053) places the cam into the bolt-on, mid-range style category. These cams work well with the stock compression, intake and exhaust. Cams with 240-plus degrees of duration or more are beginning to step into the performance arena and generally work better with other induction, compression, and exhaust modifications. Duration has a marked affect on the cams power band and drivability.
Higher durations increase the top-end at the expense of the low end. As a general rule, cams with 220-235 degrees of duration tend to produce good low end torque. Cams with 235-250 degrees of duration tend to work best in the mid-ranges and cams over 260 degrees work best for top end power.
It is important to remember here that the duration values given are to be used as a general rule and that increasing the duration will have an effect on the idle characteristics and overall drivability.
Long duration, late intake closing cam designs are necessary to drag the last bit of power out of an engine. Unfortunately, these same cams can perform poorly under more normal riding conditions. In the quest for maximum power output, many-too-many Harley owners choose a late closing, high-RPM cam for their engine. The problem with such choices is that the engine seldom spends time in the RPM range favored by such cams.
Lift: Another method of improving cam performance is increasing the amount of lobe lift. Designing a cam profile with more lobe lift results in increased duration in the high-lift regions where cylinder heads flow the most air. Short duration cams with relatively high lift can provide excellent responsiveness, great torque, and good power. But high lift cams are less dependable. You need the right valve springs to handle the increased lift, and the heads must be set up to accommodate the extra lift. There are a few examples where increased lift won't improve performance due to decreased velocity through the port; these typically occur in the race engine world (0.650- to 1.00-inch valve lift). Some late model engines with restrictive throttle-body, intake, cylinder head runner and exhaust flow simply can't flow enough air to support higher lift.
Cam (or lobe) lift is the maximum height or distance that the lifter or follower is raised off the cam. More lift generally means better top-end power, but you’ll sacrifice bottom-end response. In addition, cams with high lift typical put more wear and tear on the valve train.
For street bikes, lift figures are best kept at or below 0.500 inch, simply because, with the right cam, you can still get all the power you can use, but you won’t be needing a new valve train every 20,000 miles. Sure, with the right cylinder head/piston combination, lifts in the mid 0.500 inch range, even perhaps encroaching on 0.600 inch can work, but pushrods flex, geometry goes AWOL, and the extra benefits of the lift are quashed by the limits of flow through the ports (particularly the exhaust port), so why bother? Mega lift is more valuable to drag racers who re-engineer the whole plot any way.
The other potential problem with increasing the cam lift is that there is only so much clearance between the piston and the valve. The other problem associated with elevated lift numbers is spring fatigue. The greater the lift the farther the spring will have to expand and contract during each rotation of the cam. Cams with more lift are much harder on springs, causing a reduction in spring life.
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.
Very nice write up, very educational.......... Nice job..........
Now I have a question I hope you can help me with..........
Here is what I am working with........
1) 2013 Harley FXDF - Stock 103ci.
2) Thundermax Autotuner #309-382
3) Rinehart 2 into 1 exhaust
4) Dk Customs Outlaw Highflow 636v air intake
Just added these.
5) Andrews 48H cams
6) S&S high performance lifters
7) Screamin Eagle Quick install tappered adjustable push rod's.
Everything went together nicely no problem's, took my time to make sure no mistake's were made....
Bike runs very well, but I am experiencing some engine knock.
When I am running at a moderate rpm and slow roll on the throttle I do not experience the engine knock, at least not noticeable...........
But when I faster roll the throttle I am experiencing a very noticeable engine knock until it comes on the cam........and then it is all but gone.........
Is there any way to help cure this or make it better ??????????
I was also wondering if I am experiencing exhaust reversion as well with the design of the Rinehart exhaust ??????????
Any help you could provide would be extremely helpful...........
Very nice write up, very educational.......... Nice job..........
Now I have a question I hope you can help me with..........
Here is what I am working with........
1) 2013 Harley FXDF - Stock 103ci.
2) Thundermax Autotuner #309-382
3) Rinehart 2 into 1 exhaust
4) Dk Customs Outlaw Highflow 636v air intake
Just added these.
5) Andrews 48H cams
6) S&S high performance lifters
7) Screamin Eagle Quick install tappered adjustable push rod's.
Everything went together nicely no problem's, took my time to make sure no mistake's were made....
Bike runs very well, but I am experiencing some engine knock.
When I am running at a moderate rpm and slow roll on the throttle I do not experience the engine knock, at least not noticeable...........
But when I faster roll the throttle I am experiencing a very noticeable engine knock until it comes on the cam........and then it is all but gone.........
Is there any way to help cure this or make it better ??????????
Any help you could provide would be extremely helpful...........
Thank you for your time..........
Live Free = Ride Free............
Don't know if TM can log generic o2 data so you can find the knock area where spark advance shows spikes in the log so you can retard where needed and so forth. Don't believe TM changes spark advance on its own when zippers tried telling me how much better it was than my tts the tech guy stated timing had to be changed manually. I may be wrong but that is what I have to do once done with my can swap is get spark adv in order on top of getting ve optimized.
Don't know if TM can log generic o2 data so you can find the knock area where spark advance shows spikes in the log so you can retard where needed and so forth. Don't believe TM changes spark advance on its own when zippers tried telling me how much better it was than my tts the tech guy stated timing had to be changed manually. I may be wrong but that is what I have to do once done with my can swap is get spark adv in order on top of getting ve optimized.
Alan at Zippers said to run the idle program once the new map was installed and then to run it for a little bit do the map development (auto map) and then send them what i have and they would make the adjustments needed and send a new map. They really do not have a map for the 48H cam's...
I was just wondering if there may be something else I could to to help the issue I am having ?????? It seems to be good as long as I am running in the higher rpm's in each gear.........
I guess I need to get a little more involved with the more intricate feature's of the TM unit......
I have a question, I have a 2006 ultra classic 88inch I want to beef it up I have true duals and a six speed, and big sucker stage one air cleaner. any ideals of a good cam size that should look at I don't want to over cam I was looking at a complete 10.8:1 640 ss easy start with bigger jug and pistons pushrod and tappets but it turns the bike in to a 124in any input?
08-10-2013, 06:56 AM
Woods cams???
