355-cid small-block Chevrolet11:1 compression ratioAngle plug cylinder heads; 2.02-inch, 1.60-inch valvesMild porting (not by Speedway Testing)Chevy II oil pan1 3/4-inch fenderwell headersCompetition Cams bumpstick with the following specs:.530-inch intake lift.550-inch exhaust lift250-degrees intake duration @ 0.050 inch259-degrees exhaust duration @ 0.050 inchLobe separation of 106 degrees (installed at 102 degrees)1.5:1-ratio roller rockers780-cfm Holley vacuum secondary carb (brown secondary spring)
The tests were all accomplished with the following parameters: *Chevron 94-octane premium unleaded gasoline (see note) *Water pump driven off crankshaft *No mufflers *PCV system in place
(Note: In John's testing, he has found that Chevron fuel seems to make the best power with an air fuel ratio that appears "rich," which is in contrast to race fuels which appear to make more power with "lean" air fuel ratio numbers.)
Which Manifolds?So we had an engine. Which manifolds do we use? That was simple, too. We called High Velocity Heads, and they supplied a pair of intakes for the test: an HVH-Brodix dual-plane along with an HVH-Brodix SP1 single-plane intake. The dual-plane is a high-velocity piece designed primarily for wide-power-band street applications. It has a manifold height of 4.550 inches. In the opposite corner is the SP1. Obviously a single-plane manifold, the SP1 is a dedicated race piece with a manifold height of 5.875 inches. Meanwhile, Heida had, in his arsenal, an Edelbrock Performer RPM along with a Victor Jr. intake (both box stock). These proven manifolds would give us a good baseline. The test was set.
Testing, TestingSo far so good. What about the tests? Speedway Testing ran a number of different tests (something in the order of 15-plus pulls). Heida baselined the engine with an Edelbrock Performer RPM manifold, then swapped to the HVH-Brodix dual-plane, then swapped to the Victor Jr., and finally to the HVH-Brodix SP1. The first test, with the Performer dual-plane provided the following results:
Peak in baseline configuration was 412.9 hp at 6,200 rpm. Maximum torque was 400.6 lb-ft at 4,400 rpm (so much for the 5,500-rpm max peak power theory).