Let’s face it; if you are a car guy (or gal), this is a great time to be alive. Performance has never been easier or more powerful than it is right now. One of the most impressive routes to improved performance has to be boost. If there really is any replacement for displacement, it has to be positive pressure. The power gains offered by the many forms of forced induction are sizable, and therein lies the potential problem. While adding boost to almost any engine can improve the power output by 40-, 50-, or 100-percent (or more), this is only possible with sufficient octane. Call it power, call it torque, or even call it cylinder pressure, there is a finite limit to just how much the combustion chamber will tolerate on any given octane. The lower the octane, the lower the amount of boost and/or timing than can be run. Less timing and/or boost means only one thing, less power. In the world of high performance, race gas rules and pump gas drools!
As wonderful as high-octane race gas sounds, there is, of course, a downside: the price. The great thing about something like premium-unleaded pump gas is that it is both affordable and available, but it lacks the power-giving octane of race gas. Unfortunately, race gas is more than just a little more expensive than pump gas, so you have to decide whether the extra power potential is worth the price. For most of us, trips to the track almost always necessitate at least a few gallons of the good stuff, you know, just so we can crank it up and run a good number to go brag about to our fellow enthusiasts online. But this begs the question, what about the everyday enjoyment? Spending a few extra bucks for track trips is one thing, but having to shell out double (or triple) the price of pump gas on every fill-up is something most of us won’t even consider. What if we told you there was a middle ground, a fuel that comes straight from the pump (in many areas), costs less even than regular pump gas, and offers plenty of power-enhancing octane? What is this magic elixir? Well, the pump says E85, but it goes by the street name of corn!
The E85 designation is actually a bit of a misnomer, as it implies a mixture of 85 percent ethanol and 15 percent gasoline. Though this seems straightforward enough, the reality is that the actual blend varies greatly. According to the U.S. governing body (regulation ASTM 5798), the ethanol content of E85 can range from as low as 51 percent to as high as 83 percent. Obviously, this variation can substantially alter the tuning requirements for any combination. The reason for this is that ethanol and gasoline have different stoichiometric values (the ideal ratio of air and fuel to support complete combustion). For gasoline, the stoichiometric value is 14.7:1, while E85 is 9.8:1. What this means is that it requires more E85 to reach the same air/fuel mixture as gasoline. What this also means is that some of the cost savings of E85 (being less expensive at the pump compared to pump gas) is offset by increased fuel usage (meaning a reduction in fuel mileage). The ethanol can also be corrosive to some fuel systems not designed for the alcohol-based fuel. As we mentioned earlier, and the reason for this test, is that E85 has a much higher octane rating than pump gas. In fact, the Rockett Brand E85 we tested rivaled the 114-octane race gas we compared it to. As a side benefit, the ethanol-based E85 offered a substantial decrease in inlet air temps, further warding off harmful detonation, irrespective of the increased octane.
Now that we know the pluses and minuses of E85, let’s see how well it works. Right off the bat, any contest between 112-octane E85 and premium unleaded pump gas (91- or 93-octane) would be no comparison. The E85 offers more power, even before we get into the added ability to run more timing and/or boost from the lack of octane on the pump gas. Knowing this, we decided to compare the E85 to race gas, in this case, Rockett Brand 114-octane. The use of race gas allowed us to run full timing on both of our blower combinations and demonstrate the added benefits of just the E85 (with no changes to the A/F ratio, timing, or boost). For our engine, we chose our power-adder ready BluePrint Engines 383 stroker test mule and opted to try this test on two very different blowers: a Weiand 6-71 roots and a ProCharger F-1A-94 centrifugal unit. So let’s see how corn can help your blown engine push out more power.
Photos by Richard Holdener