An engine dyno shows you the...
An engine dyno shows you the results of a pull immediately, making it easy to compare the numbers from one pull to the next. We saw gains in each spacer we tried, but our engine seemed to like open spacers, making its best power with a 2-inch open unit.
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.
Conclusion
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.
We made dyno pulls using several...
We made dyno pulls using several different-size and -style spacers under the Quickfuel 1,000-cfm carb, showing power with each.
We made dyno pulls using several...
We made dyno pulls using several different-size and -style spacers under the Quickfuel 1,000-cfm carb, showing power with each.
We purposely cut the valve...
We purposely cut the valve reliefs in our pistons deeper than needed so we could try different camshaft timings while on the dyno.
Thanks to our Jesel beltdrive...
Thanks to our Jesel beltdrive timing system, this is not only possible but easy.
We chose a solid-roller camshaft...
We chose a solid-roller camshaft and lifters from Comp Cams, and had the company grind it to the LS firing order. Compared with a traditional SBC, this swaps the Nos. 4 and 7, as well as the Nos. 2 and 3 cylinders.
Advancing cam timing using...
Advancing cam timing using the Jesel beltdrive moved the powerband of the engine lower in the rpm range, while retarding cam timing had the opposite effect. We found our engine made the best average torque and hp between 4,000 and 7,000 rpm with the cam installed at 106 degrees—right where Comp recommended.
If you’re using a hydraulic...
If you’re using a hydraulic camshaft, there’s not a whole lot to be gained by experimenting with valve lash. With solid lifters, however, the proper lash can have an effect on the engine’s peak performance.
Tightening intake-valve lash...
Tightening intake-valve lash can make more peak power, but our engine posted the best torque and hp numbers with the valves set right at Comp’s specs of 0.018 intake and 0.020 exhaust. Not everything you try on the dyno results in added power, but it sure is easier to make these adjustments on the dyno than it is while leaning over the fenders.