Our E-85 fuel conservatively made 25 more horsepower than the 91-octane fuel, across the entire power spectrum. We didn't change anything except the fuel, so why did this occur? One very noticeable difference was the maximum temperature in the intake plenum ran 55 to 68 degrees cooler with E-85 than with the 91-octane. We were vaporizing 25- to 30-percent more fuel, with nearly twice the latent heat of vaporization of gasoline, and it cooled the charge. Cooler intake plenum temperatures mean more power. The difference will naturally be less on naturally aspirated engines, but it should still be there. The air temperature above the carburetor and the exhaust temperature was nearly identical with both fuels, so nothing to talk about there.
Could we gain even more with E-85? We think so. Cooler intake plenum temperatures in combination with E-85's 105-octane should allow more compression, more boost, or even more timing than 91-octane without encountering detonation, and this should yield more power.is E-85 a viable option for you? That's a hard question to answer. First, is E-85 readily available in your area yet? Are you willing to change your engine's current tune to efficiently run E-85? There are a lot of factors that have not been explored yet and will come to light with long-term usage, but for now, E-85 does sound like it will be a viable choice in alternative fuel sources that our musclecars will be able to live with.
For the comparative 91-octane pump gas versus E-85 dyno pulls shown in the subject article, the 4150 HP Holley carburetors were jetted as follows:
- 91-octane carburetor: 82 primary and 82 secondary jets
- E-85 carburetor: 90 primary and 96 secondary jets
- Lambda readings during the dyno pulls:
- 91-octane fuel: .735 at 3,000 rpm, increasing to .850 at 6,000 rpm
- E-85 fuel: .753 at 3,000 rpm, increasing to .856 at 6,000 rpm
- Stoich readings during the dyno pulls:
- 91-octane fuel: 10.8 at 3,000 rpm, increasing to 12.5 at 6,000 rpm
- E-85 fuel: 7.3 at 3,000 rpm, increasing to 8.3 at 6,000 rpm
Editor's note: There are a couple of concerns about E-85 fuel that we felt our readers should also be aware of. One concern involves the fact that E-85 is generally blended with 15-percent unleaded gasoline at the pump, and this could invariably affect the consistency of the fuel from station to station. This variation may not affect you if you're not eeking out every last bit of horsepower available, but if super-tuning, the difference could mean that some timing changes may need to be made as blending differences could be affected by the content properties of the unleaded fuel being used in the mixture. The second concern with E-85 is the price. While this fuel seems less expensive than gasoline, it actually costs more to produce. The low price of E-85 is partially due to the federal government subsidizing the fuel at a rate of some 51 cents per gallon. Once E-85 is generally accepted and used, we wouldn't be surprised if this subsidy goes away, and E-85 may soon be taxed as a motor fuel, making it somewhat more expensive than gasoline