Iron Heads,Blowers, and E85
If you remember our story on the Magnuson 122ci High Helix blower, then you also know we made an astonishing 504 hp and 512 lb-ft of torque with nothing more than cast, flat-top pistons, a mild hydraulic flat-tappet cam, unported iron GM Vortec heads from Scoggin-Dickey, a set of headers, and a simple 750-cfm Holley carburetor.
By substituting E85, we wanted to see the difference in power we could generate with a much higher-octane fuel and also see the benefits from the fuel's greater inlet-air-charge cooling ability. We planned to push this little small-block to the limit on cylinder pressure, so the idea of cast pistons pushing well past 500 hp didn't inspire confidence. We decided to increase the durability factor by adding a set of forged flat-top pistons. We found a Speed-Pro forged flat-top, 0.030-over piston kit with 11/416-inch rings from Summit Racing for less than $350, which fit into our budget perfectly. Combined with the 64cc iron Vortec heads, this pushed the compression ratio up from the cast-piston ratio of 8.6:1 to a far more aggressive 10.2:1. We obviously had to bore and torque-plate-hone the block, and the entire rotating assembly had to be rebalanced, which was ably handled by Jim Grubbs Motorsports.
This is not a normal compression ratio for a supercharged engine, but the idea here was to push the cylinder-pressure envelope. This also meant our spark timing would have to be very carefully curved to prevent over-advancing the timing and causing detonation, even with E85's 105-octane rating. We also stepped up to a stronger spark with a Mallory electronic distributor and HyFire VI spark box.
We retained the Crane PowerMax 288 flat-tappet hydraulic blower cam that we used in the first test. The iron Vortec heads along with the higher compression didn't cause any detonation problems, and we quickly achieved 555 lb-ft of torque, a gain of more than 40 lb-ft of torque over pump gas, and 519 for horsepower, a jump of exactly 15. As we expected, torque improved with the combination of the additional compression and the ethanol fuel. The horsepower gain we saw with this blower test is attributable to the roughly one-point-higher compression ratio, which is worth about 3 percent, equal to roughly 15 hp.
We were on our way to an even more aggressive boost curve when the two pressed-in studs for cylinder No. 4 pulled out of the head and shut down that cylinder. We decided to swap on a better set of heads rather than to try to fix these production castings.