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.
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