Engine Cams - Got Lobes

VALVETRAIN CHECKLIST
If the most frequent mistake cam swappers make is choosing the wrong cam, the second is most certainly neglecting to upgrade the rest of the valvetrain to go with the new 'stick. "Many people may not fully appreciate how each part has to work together," says Knight. "And creating a good, stiff valvetrain is critical." Special attention should be paid to the valvesprings--just because what's already in your cylinder heads can handle an increase in lift doesn't mean they've got the necessary spring rate or pressure for the new cam profile. There's a host of things to check when stepping up your cam--run through this list and you'll have your bases pretty well covered.

LIFTERS	Make sure you use the correct lifters for your application. "You can't run hydraulic lifters on a mechanical cam, either flat-tappet or roller," warns Knight. "The incompatible lobe designs can possibly lead to the lifters literally exploding." Never reuse flat-tappet lifters--either solid or hydraulic--on a new cam. These mate to the cam lobe during initial break-in and won't wear in properly on a new cam. Be sure to use a break-in oil and either oil additive or diesel oil when first running a hydraulic or solid flat-tappet cam. It may also be a good idea to remove the inner valvesprings for break-in if you're running high spring pressures. Roller lifters--either solid or hydraulic--can be reused if they're in good shape.
PUSHRODS	Many guys try to save a buck when it comes to buying pushrods, but investing in good, stiff pushrods can pay dividends. "We took a `nothing' motor, put in good pushrods, and all the little sags and dips came out of the powerband," says Knight. "We've seen increases of 7-9 hp with a pushrod upgrade." Hold off on buying pushrods when you buy your cam and lifters. Instead, use a pushrod length checker to determine the proper pushrod length, then order them. In short, the proper pushrod length is the one that yields correct valvetrain geometry. *Check pushrod-to-head clearance whenever changing a cam or other valvetrain components.
ROCKER ARMS	Traditional stamped-steel rocker arms are fine for stock applications, but any performance application should be using a good set of roller rockers--they're more rigid and cut down on power robbing friction. Increasing rocker arm ratio by a point (e.g., 1.5:1 to 1.6:1) increases valve lift by approximately 0.030 inch and adds 2-4 degrees of duration--most cams specs base valve lift on a 1.5:1 rocker. *Self-aligning rockers shouldn't be used with guideplates.
SPRINGS AND HARDWARE	Always use springs that are appropriate for your type of cam and are made to handle your intended lift figures and rpm levels. Don't assume the springs you already have will work. Cam manufacturers spell out the spring needed for each application for good reason. "You should never cheap out on valvespings," says Knight. Check for valvespring coil bind--there should always be at least 0.060 inch between both the inner and outer coils. Likewise, be sure to use the correct retainers and locks with your springs. Check just about any cam catalog, and the proper hardware will be specified. Check for rocker arm-to-retainer clearance--you should have at least 0.030 inch. Once you have the proper valvespring, be sure to set it up properly--the installed height and seat load are listed on the end of the box. Remember to check for retainer-to-valveguide--or seal--clearance. The distance between the two should be greater than the valve lift you're running. *Use of a spring locator, or cup, is mandatory on aluminum heads, and not a bad idea in any case.
VALVES	*Be sure to check piston-to-valve clearance whenever you change a cam or any other valvetrain components. You need a minimum of 0.100 inch on the intake and 0.125 on the exhaust.

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