10 Questions About Camshafts And Valve Train Components
1. How do I go about selecting a cam based on my desired engine rpm range?
Many variables determine the rpm range and torque curve –the “powerband” of an engine, including cubic inch displacement, cylinder head characteristics, intake manifold, camshaft specifications and others. Note that larger displacement engines require more duration than smaller ones because they require more air/fuel mixture to fill their larger displacement cylinders.
The most important aspect of camshaft (and other component) selection is to have your specific rpm “goal” in mind before you begin to select engine parts. A camshaft should be close to the last item on your list –chosen to match all of the other performance pieces on your engine. Remember that the best way to select a camshaft is to ask an expert to help you select the right camshaft based not only on the size of your engine, but on your entire combination of parts.
When seeking assistance in selecting a camshaft, it is important that you can provide the weight of your vehicle, transmission type, converter stall speed, rear end ratio, engine displacement, compression ratio, and whether it will be normally aspirated, or if you intend to run a power adder such as nitrous, a turbocharger, or a supercharger. Each of these variables must be considered when choosing a cam, and the more accurate the information – the better your new camshaft will perform.
2. What is the difference between intake centerline and lobe separation angle?
These two terms are often confused. Lobe separation angle (LSA) is simply that: the number of degrees (denoted by the ‘°’ symbol) separating the peak lift points of the intake and exhaust lobes. Lobe separation is effectively “locked in” when a camshaft is ground and cannot be changed. Note that a tighter lobe separation (smaller LSA number) results in a narrower and peakier torque curve, and a wider lobe separation (larger LSA number) produces a broader torque curve.
The intake centerline is the position of the centerline (or peak lift point) of the intake lobe in relation to the Top Dead Center position of piston travel. Intake centerline can be adjusted by degreeing your camshaft, and can have the effect of increasing off-idle torque (advancing) or increasing peak RPM (retarding) .
For example, if your camshaft has a 110° LSA, and you install it with 4° advance, your intake centerline is 106° after Top Dead Center.
3. My motor is currently naturally aspirated, but I plan on installing a power adder. Can I use the same cam for both applications?
Normally aspirated (N/A) engines and boosted engines generally require different camshafts for optimum efficiency. Typically, camshafts intended for use with power adders will feature a wider LSA and more exhaust duration than those intended for use in a non-boosted application.
A few important points:
• Each type of power adder is different and so are the cams that work best with them. Variables such as boost pressure or nitrous horsepower shot must be taken into consideration to ensure consistent performance.
• Nitrous creates a lot of cylinder heat and requires more exhaust duration to help evacuate the cylinder.
• Superchargers also increase cylinder heat and tend to work more efficiently with a wider lobe separation.
• Turbocharger technology has come a long way. Again, many variables should be considered, but in general you don’t need a very large cam. Turbo cams in fact, should have less exhaust duration than a N/A cam.
4. How does increasing or decreasing duration affect my engine performance?
Duration has a tremendous amount of affect on engine behavior -most notably, the rpm at which its peak torque is produced. Shorter duration camshafts (or “mild” cams) produce more low rpm torque, while camshafts with larger duration (or “bigger” cams) will tend to increase upper rpm horsepower at the expense of low rpm torque. In general, for every 10° increase in duration, the torque peak of the engine moves up by 500 rpm.
5. I currently run a solid flat tappet cam. Is it worth the investment to upgrade to a solid roller cam?
The simple answer to this question is yes -if it’s in your budget. Solid roller designs use the latest and most advanced profiles that we offer. Among the benefits are reduced valve train friction, higher engine rpm capability, and use of faster ramp profiles, which generate higher power and torque by snapping the valve open and closed more quickly.
Solid roller camshafts and related component technology has come a long way in the last 10 years. Today, a solid roller setup can be durable and offer incredible performance. COMP Cams® offers a high quality, Endure-X™ lifter which features a tool steel axle, EDM Oil Injection and precision sorted needle bearings.
Endure-X™ lifters are available for a variety of engines with different offsets and lifter body heights.
6. How does compression ratio affect camshaft selection?
The key factor to consider here is cylinder pressure. If you have a lower compression motor, say 9.5:1, and you use a camshaft that is fairly large (increased overlap between lobes –which allows both the intake and exhaust valves to be open at the same time) then you will bleed off cylinder pressure and in effect – horsepower and torque.
On the other hand, if you’re running a high compression race motor and your camshaft has a minimal amount of overlap, the cylinder pressures can go sky high. This is far less of a problem for race engines than it is for street-bound engines, but it should be considered and factored in at the time that you choose your cam. In addition, the type of cylinder heads that you’re using and the quality of available fuel should be taken into consideration. If you have to stick with pump gas, the rule of thumb is to limit compression to 10:1 with cast iron heads and 11:1 compression with aluminum heads.
7. I have heard stories about people having issues with flat tappet break in. What does COMP Cams® offer to help reduce the chances of flat tappet failure?
Due to federal legislation, motor oils no longer contain certain anti-scuffing agents that played a critical role in flat tappet camshaft break in. While incorrect valve spring pressure and not following proper break-in procedure are often the culprits, the changes in oil formulation have brought about a need for additional steps to be added to the break-in process.
COMP Cams® has two ways to ensure proper break-in of flat tappet cams.
COMP Cams® Engine Break-In Additive (part #159) ensures that the camshaft will have the lubricants that it needs to seat the camshaft journals and lobe/lifter surfaces. This lubricant is poured into the engine crankcase after the camshaft and lifters have been coated with the initial break-in lubricant supplied with the camshaft.
Another option for increasing flat tappet cam longevity is nitriding. Recently COMP Cams® invested in a nitriding machine, the first of its kind owned by a major U.S. aftermarket camshaft manufacturer. Nitriding actually hardens the surface of the camshaft and tappet face by injecting nitrogen “needles” into the metal. The result is an ultra-hard surface on the face of the camshaft lobes and lifter face, which greatly improves the performance and break-in process for flat tappet cams. This process is an additional charge for COMP Cams® camshafts, but for many extreme duty applications, it virtually ensures proper break-in and increased durability.
8. I’m switching from carburetion to fuel injection. Do I need to change my camshaft?
Quite frankly, it depends on what camshaft is already installed in your engine, but for the most part, yes. The important thing to remember is that factory fuel-injected engines generally require wider lobe separation angles than carbureted engines do. Camshafts with wider LSAs feature decreased overlap, which yields a more efficient combustion process and increased vacuum, which is required by factory engine computers (or “ECUs”).
In order to take advantage of the design characteristics of the high efficiency EFI-style cylinder heads and intake systems, COMP Cams® offers specialized fuel-injection camshafts, such as the XFI™ series. These cams deliver dramatic improvements in performance for today’s fuel injected engines while still satisfying the requirements of sensitive OE computers.
Aftermarket engine computers such as the FAST™ XFI™ system can run cams in street and competition applications that would traditionally be considered suitable for carburetion only, but these ECUs are the exception, not the rule.
9. What pushrod length do I need and which style pushrod is best for my application?
Pushrod length and rocker arm geometry are critical to an engine’s performance and longevity. Pushrod length should always be measured in a performance engine because no two engines are exactly the same.
Widely varying machine work quality, cylinder head casting variances, hundreds of possible camshaft base circle diameters, and many other variables all affect the pushrod length required to achieve correct rocker arm geometry.
Pushrod diameter, though not directly effecting rocker geometry, must also be appropriate to your application. The general rule of thumb is to use the largest diameter pushrod that your engine will accept. COMP Cams® offers pushrods in various diameters, materials, lengths, and wall thicknesses to meet your specific needs.
For a mental picture of the forces that your pushrods must withstand, imagine this: the pressure being applied to even one of your pushrods at high engine speeds is equivalent to the pressure that would be applied if your entire car’s weight was being supported by that pushrod. That is why winning racers don’t try to save money in this area –instead buying the best quality pushrods that they can find.
10. How does changing my valve lash affect the behavior of my motor?
Adjusting your valve lash by adding or subtracting a few thousandths of an inch will respectively reduce or increase your camshaft’s duration, thus affecting your engine’s performance.
Running tighter valve lash (reducing the amount of clearance between the rocker tip and the valve stem) will make the cam profile larger (more duration) and increase your upper rpm horsepower. Loosening the valve lash does just the opposite by decreasing camshaft duration -promoting low rpm torque and improving your 60-foot time and/or ability to accelerate out of turns. The general rule of thumb when adjusting valve lash is that 0.004” of adjustment from the valve lash specified in the cam card equates to a 2° difference in duration when measured at 0.050” lift.
Although the overall effect on performance is obviously not as dramatic as making a camshaft swap, knowledgeable racers have successfully used this tuning trick to win races by adjusting valve lash in order to take maximum advantage of track conditions.
COMP Cams® Tech: Cam & Valve Train FAQs 
Linear Mode
