Engine Dyno - Build Your First Engine

Aluminum heads expand more than iron heads once normal operating temperature is reached. The Isky cam card recommends 0.016/0.018 valve lash clearance. If set cold, this will grow by around 2 to 3 thousandths in the running engine. Some guys will remove a few thousandths from the cold setting (0.013/0.015 in our case) and leave it at that. But for complete accuracy, you really should set them to the recommended spec with the engine cold then recheck them after it warms up like we did on our Scorpion billet aluminum roller rockers.

All buttoned up, in Test 3 (aluminum heads, dual-plane), the Super Street 215 heads and RPM Air Gap made 431 hp at 5,700 rpm and 441 lb-ft at 4,800 rpm, an impressive 52hp and 36-lb-ft increase over the results of Test 1 (iron heads, dual-plane). Clearly the added 0.8 point of compression, free-breathing ports, and bigger valves boosted cylinder pressure and exerted more leverage on the crankshaft. What's really good to see is how the aluminum heads were already outperforming the iron heads by 26 hp and 45 lb-ft way down at 3,000 rpm, where the dyno started measuring output.

Test 4 (aluminum heads, single-plane), netted 442 hp at 5,800 rpm and 436 lb-ft at 5,000 rpm. The resulting 11hp gain and 4.5-lb-ft torque loss reaffirm the high-rpm bias of the single-plane design. Look at the dyno printout; the single-plane lags behind the dual-plane in every area until 5,000 rpm, where the single plane finally delivers higher horsepower and torque numbers. So unless you're planning on spending more driving time above 6,000 rpm than below 5,000-rpm, stick with a good dual-plane manifold, you'll be a car length ahead. Next time we'll stick it in a car and see what it does on the chassis dyno and dragstrip. See you then!