This shows how much cutting was done before the new, hardened intake seat was pressed in.
In addition to its complete inability to live in harmony with oil, alcohol also requires other considerations when switching over from gasoline. One factor is that the ideal air/fuel ratio for alcohol is around 7:1, more than twice that of gasoline which burns best at a ratio of 14.5:1. This accounts for the extra demand on the fuel pump. Another factor is that alcohol is more resistant to detonation and can typically live with a higher compression ratio. This is because it burns cooler and much more fuel is traveling through the combustion chamber than a gas engine. Troutman took advantage of this by retarding the cam timing two degrees over his regular setup.
Once the fuel pump is in place, the extra fuel demands can be handled simply by swapping out carburetors. For gasoline, this engine will run with an 830-cfm Holley four-barrel with 85-size jets. Alcohol requires a big step up. In place of the 830 carb, a 900-cfm annular discharge Holley is bolted up, and the jets are bumped up in excess of 188. The end result, though, is that conversion from gasoline to alcohol or vice versa is a relatively simple process. Just swap carburetors, adjust the fuel pump (or replace the belt-driven pump with a standard unit), and make a timing change (max power on gasoline was at 22 degrees, while alcohol seemed to run best at 21 degrees of timing).
On the Dyno
The dyno test was set up in two distinct stages. First, the engine was configured for gasoline (fuel pressure and carburetor) and dyno tuned. Then everything was performed again in the alcohol-burning configuration. The gas combo worked best with the timing set at 22 degrees, creating a peak horsepower number of 615.4 at 6,800 rpm and a broad torque powerband in excess of 535 lb-ft from 4,800 to 5,900 rpm. Volumetric efficiency maxed out at 92.6 percent at 5,200 rpm.
The cam timing was retarded two degrees over Troutman's normal setup for gasoline.
Alcohol performed best at 21 degrees advance timing. Max power jumped 39.8 hp to 655.2 at 6,400 rpm. Torque also increased (542.9 lb-ft at 6,300 rpm), although it moved higher in the rpm range. More power could possibly be found in this combination with a little more effort. The engine was again showing signs of beginning to run slightly lean at the upper rpm limits. The easy solution is simply to switch out for larger jets, but 188s were already in the carburetor and Troutman didn't have any larger jets in his shop.
"We could have spent the time and made the minute adjustments to tune every last ounce of power out of it," he explains, "but practically speaking, that wouldn't do much good. I'm in North Carolina and the customer is in West Virginia, so even if I got the perfect jet in it for the elevation and atmospheric conditions here, it's going to be wrong for him at his home track. Plus, I'm also running headers that aren't ideal. They are 1 5/8 inches with no step-up feeding into 3-inch collectors. This engine could use larger pipes. It would help increase the high-rpm power and keep it from falling off on the top end, but since the exhaust restriction was consistent from the gasoline test to the alcohol test, it really doesn't matter that much. The test here was to see the difference in how the engine handled the two different fuels-not to get a single horsepower number to go home and brag about."
In an effort to make the comparison results as accurate as possible, some changes that could have been made to improve peak horsepower (jet changes, header pipe changes, etc.) were not made. Unfortunately, all these changes seemed to especially hurt the power after peak when burning alcohol. Troutman felt that a few simple changes could have significantly helped the alcohol numbers to keep from dropping after the horsepower peak. Overall, we were very happy with both the power and torque curves this engine produced burning both fuels.