Big Heads Equals Big Power
Superchargers employ a very simple power plan. Use lots of pressure to stuff the air and fuel into the cylinders. The little Vortec heads are great for mild power, but realistically, their tiny intake ports created a restriction in our path for more power. What we really needed was a pair of heads that could flow some big-time air. We decided to go with a pair of TFS 215cc intake-port heads that would offer some serious airflow capability. The only serious change this demanded was a swap to a different Magnuson supercharger intake-manifold base, since the TFS heads use the standard small-block Chevy intake bolt pattern, not the Vortec pattern.
We began testing the TFS heads with the same tune-up as the prior Vortec heads, and the power jumped slightly. As we began to tune the combination, add more timing, and bump up the boost by running a smaller blower pulley, the power numbers really jumped. This put us well past the 600 lb-ft of torque range and boosted the horsepower right past the 575hp mark. Up to this point, most of our tuning efforts had been very successful. With between 8 and 9 psi of boost pressure and with timing set at 35 degrees total, we now had the power at 616 lb-ft of torque and 584 hp.
The final tweak was going with slightly richer high-speed air bleeds. Tuning with the Innovate Motorsports air/fuel ratio meter, it appeared that a Lambda reading of 0.75 (roughly equivalent to an E85 air/fuel ratio of 7.25:1) was where the engine made best power. This change, along with a smaller blower pulley and exchanging the high-ZDDP-level diesel 15W-40 oil for some Quaker State High RPM synthetic 5W-30 kicked us over the top of 600 hp, at which point heavenly angels began to sing and there was rejoicing in Car Craft land. When our little 355ci small-block pushed past 600 hp, we were thrilled.
What's impressive is this is a tiny little 122ci supercharger sitting on a mundane 355ci small-block Chevy with medium-size ports and a very mild hydraulic flat-tappet camshaft running on E85 fuel. Another amazing result of this test was the blower discharge temperatures. At 8 psi at 5,700 rpm, the air temperature exiting the blower and entering the intake ports was a mere 91 degrees F. Granted, our carburetor inlet air temperature was a conservative 70 degrees, but mixed with the E85, the alcohol (along with a very efficient Magnuson supercharger) kept the discharge temperature very low. That's the big reason, along with E85's 105-octane rating, this engine never rattled.