Tom Wilson
December 27, 2013

Regardless of the pork politics and sketchy economics of ethanol production in this country, you have to admit the stuff makes for great race fuel. Widely available in the Midwest, where it’s produced in great volume from corn, ethanol is making its way to both coasts as a motor fuel.

In fact, high-ethanol content fuel is now available out of the pump or in drums on the West Coast, specifically in the Los Angeles and San Diego regions. It’s called E85, denoting the liquid being pumped is 85 percent ethanol and 15 percent gasoline. Obviously this is different than the standard pump gasoline, which is E10, or 10-percent ethanol and 90-percent gasoline.

Widely despised, E10 seems the wrong combination—it doesn’t have enough ethanol to gain the benefits of an alcohol-based fuel, but does have enough alcohol to increase water absorption (boaters hate it) and reduce the heat energy of the fuel. In other words, it’s not the best stuff to store all winter in your gas tank and your fuel mileage drops about three percent. But E85 is different. Its high alcohol content raises octane significantly (see sidebar), allowing increased ignition timing or boost. In practice, it’s increased boost that’s the major player in the 800-1,000hp dynosheets E85-burning Mustangs have been churning out.

Another big plus is that corn—E85 in the drag racer’s argot—is far less expensive than racing fuel. Currently the benchmark high-octane race fuel is C16, a gasoline elixir that cures whatever ails your race engine with its studly 116-octane rating. However, C16 is $17 a gallon, is not pumped at any neighborhood gas station, and contains lead. That means it coats oxygen sensors into uselessness and clogs catalytic converters even faster.

In contrast, E85 contains no lead or other metals, has reduced hydrocarbons so it burns far cleaner than gasoline, and is dispensed as a flex fuel at local gas stations for under $4 a gallon. In fact, it’s typically a few pennies less expensive than regular 87-octane rotgut.

There are downsides to E85. The most obvious is it’s not readily available unless you live near an E85 pump. But there are a growing number of enthusiasts who do.

Secondly, E85 has notably less heat energy than gasoline, and its stoichiometric air/fuel ratio is much lower than gasoline—a shade under 10:1. This means you have to burn more of it to make the same amount of power. Again, increased ignition timing and boost offset this loss ever so slightly, but even the most ardent E85 fan will tell you your mileage will vary—downward by about 30 percent. That does offset its lower cost and makes the Mustang’s already small fuel capacity seem even smaller. There are corrosion issues as well.

Jim Bell, the big rotor at Kenne Bell, became interested in E85 after Adam Montague of Spankn’ Time Motorsports ( began raving about it. Adam is an accomplished modular V-8 tuner, and was himself drug into tuning E85 by an early adopting customer who insisted his Mustang was going to burn the stuff. As E85 came to Jim Bell, there were many unanswered questions, plus all the usual hype and Internet chatter confusing the facts. In typical fashion, Jim and righthand man Ken Christley went to the lab and dyno to science out the reality of E85 and how to best make horsepower with it on supercharged engines.

To save everyone breathless anxiety about how much power is possible with E85, one of Adam’s tunes using a Kenne Bell 3.6-liter Liquid Cooled supercharger at 18 pounds of boost netted 820 rwhp from his Coyote. At the strip on slicks with minimal suspension upgrades this was good for a 9.8 second pass at 142 mph; on the street (the old guys are shaking their heads ...), Adam prefers to pulley the car right at 800 rwhp, still on E85. More on all this as we go along, but be assured E85 helps make power and is quite streetable.

As Jim and Ken got on with their testing, they concentrated on the fundamentals of how E85 works rather than simply trying to make maximum horsepower. That’s more of what Adam does at ST Motorsports, so there was no need to duplicate his work, but rather a need to provide an understanding of E85’s properties. Areas Kenne Bell explored were comparing E85 to C16 race fuel; different air/fuel ratios and how they affected E85 power production; exhaust gas temperature studies; fuel flow comparisons with C16; air/fuel ratio compared to fuel pressure (important due to the high flow rates required with E85); and boost tolerance of C16 and E85.

At all times the emphasis was on E85 as a race fuel. Yes, it runs just fine on the street, and Adam loves the stuff there despite its lousy fuel economy. If your Mustang is a dedicated weekend toy then switching blower pulleys and draining fuel tanks are a pain and you might as well run E85 all the time. But to Jim Bell the idea is to run a large blower pulley and premium pump gasoline on the street, a combination that puts 550 hp or so to the tires, then install a small pulley and E85 for track duty. Conceptually this is identical to what Kenne Bell has been advocating for years with C16 race fuel. The big difference is E85 is far cheaper and doesn’t ruin cats or oxygen sensors, so there are no hassles either swapping cats on track day or running without them on the street.

It would take a small book to run through all of Kenne Bell’s E85 testing, so we’ll just hit the highlights. Perhaps the most basic question was, because E85 is so oxygenated, does it make more power than C16? The answer is yes, but not the 100hp gain rumored by pit chatter.

With a 650-rwhp tune, KB’s testing shows E85 is good for a solid 35 extra horsepower over C16 gasoline. This testing was careful to avoid variables and was repeated multiple times according to Jim.



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Air/Fuel Calculator

Lambda 100% Gasoline E10 E15 E85 Methanol
1.238 18.12 17.42 17.07 12.19 7.92
1.224 17.92 17.23 16.88 12.05 7.83
1.210 17.72 17.03 16.69 11.92 7.75
1.196 17.51 16.84 16.50 11.78 7.66
1.183 17.31 16.65 16.31 11.64 7.57
1.169 17.11 16.45 16.12 11.51 7.48
1.155 16.91 16.26 15.93 11.37 7.39
1.141 16.70 16.06 15.74 11.23 7.30
1.127 16.50 15.87 15.55 11.10 7.21
1.113 16.30 15.67 15.36 10.96 7.13
1.100 16.10 15.48 15.17 10.83 7.04
1.086 15.90 15.28 14.98 10.69 6.95
1.072 15.69 15.09 14.79 10.55 6.86
1.058 15.49 14.89 14.60 10.42 6.77
1.044 15.29 14.70 14.40 10.28 6.68
1.030 15.09 14.50 14.21 10.15 6.59
1.017 14.88 14.31 14.02 10.01 6.51
1.003 14.68 14.11 13.83 9.87 6.42
1.000 14.64 14.08 13.79 9.85 6.40
0.989 14.48 13.92 13.64 9.74 6.33
0.975 14.28 13.73 13.45 9.60 6.24
0.961 14.07 13.53 13.26 9.46 6.15
0.947 13.87 13.34 13.07 9.33 6.06
0.934 13.67 13.14 12.88 9.19 5.98
0.920 13.47 12.95 12.69 9.06 5.89
0.906 13.26 12.75 12.50 8.92 5.80
0.892 13.06 12.56 12.31 8.78 5.71
0.878 12.86 12.36 12.12 8.65 5.62
0.864 12.66 12.17 11.92 8.51 5.53
0.851 12.45 11.97 11.73 8.38 5.44
0.837 12.25 11.78 11.54 8.24 5.36
0.823 12.05 11.58 11.35 8.10 5.27
0.809 11.85 11.39 11.16 7.97 5.18
0.795 11.64 11.20 10.97 7.83 5.09
0.782 11.44 11.00 10.78 7.69 5.00
0.768 11.24 10.81 10.59 7.56 4.91
0.754 11.04 10.61 10.40 7.42 4.82
0.740 10.83 10.42 10.21 7.29 4.74
0.726 10.63 10.22 10.02 7.15 4.65
0.712 10.43 10.03 9.83 7.01 4.56
0.699 10.23 9.83 9.64 6.88 4.47
0.685 10.02 9.64 9.45 6.74 4.38
0.671 9.82 9.44 9.25 6.61 4.29
0.657 9.62 9.25 9.06 6.47 4.21
0.643 9.42 9.05 8.87 6.33 4.12
0.629 9.21 8.86 8.68 6.20 4.03
0.616 9.01 8.67 8.49 6.06 3.94
0.602 8.81 8.47 8.30 5.92 3.85
0.588 8.61 8.28 8.11 5.79 3.76
0.574 8.40 8.08 7.92 5.65 3.67
0.560 8.20 7.89 7.73 5.52 3.59
0.546 8.00 7.69 7.54 5.38 3.50

This chart compares methanol (the other alcohol fuel), ethanol, gasoline, and the three popular ethanol/gasoline blends. It’s a handy tuning reference when deciphering Lambda-meter readings, or when simply educating yourself on how these different fuels want to mix with air. Thanks to Ken Christley for generating the chart.

Horse Sense: Alcohol comes in two varieties: methanol, which comes from wood; and ethanol, which comes from grains. Your car can drink both kinds—you cannot. Ethanol is the stuff in beer; methanol is a deadly poison.