Most camshaft manufacturers recommend a certain valve lash for their solid-lifter cams, indicating the best all-around setting for these components. Engine variables such as aluminum construction, pushrod flex, and rocker design can all make a difference in the initial valve-lash setting, as well as in how well the engine retains its lash. So while it's important to properly set the valve lash in an engine and check it periodically, valve lash can be used to tune the engine as well.
Since a solid-lifter cam requires clearance between the rocker arm and valve stem, adding to or subtracting from that clearance can add to or subtract from lift and duration. We thought our cam was matched pretty well to the rest of our combination, but we decided to experiment with valve lash just to see.
By tightening the intake lash by 0.008-inch, we effectively increased the valve lift as well as the duration. A pull on the dyno indicated a loss of power, however, meaning our cam is plenty big for this combination. By loosening the intake then exhaust lash we lost power as well, winding up with the valve lash set at 0.018-inch intake and 0.020-inch exhaust, just as Comp recommends. This is a good example of how a change you might think would help can actually take power away from the engine. It's also an excellent example of why it almost always pays to follow to the manufacturer's recommendations.
While there's no perfect recipe of fuel, air, ignition, and camshaft timing that works for every engine, the engine dynamometer makes tuning an efficient operation that can be accomplished in a controlled environment. The feeling of being able to drop the engine into your Corvette knowing it will run its best from the outset easily offsets the cost of dyno rental. All told, we netted an additional 20 lb-ft of torque and nearly 40 hp by dyno tuning our engine, meaning more time having fun in the car and less time searching for the proper combination.
Be sure to watch future issues of VETTE, as we install this potent small-block in project C3 Triple-Ex. And be sure to visit www.vetteweb.com to check out how this project has taken shape.