E85 is a highly oxygenated fuel consisting of 85% ethanol and 15% gasoline. Many motorsports enthusiasts overlook E85 for performance applications because they associate it with low performance, flex-fuel vehicles. This primary usage of E85 does not take advantage of any of its potential performance advantages. Key benefits of E85 wasted on flex-fuel cars are: high oxygen content, evaporative cooling, higher octane and lower exhaust gas temperatures (EGTs). All of these can be exploited when looking at building a boosted car. Properly executed, the result should be more horsepower per dollar with improved street-ability.
Forced induction or boost are terms used to describe processes for pressurizing an engine’s intake air charge. This puts more air and fuel into the cylinders in order to generate higher horsepower. Boost can be applied to an engine with either a supercharger or turbocharger. Superchargers compress the intake air using power from the crankshaft while turbos use the velocity of the exhaust gas to achieve the same effect. Regardless of how you compress air, heat is generated. Ideally however, the intake air should be as cold as possible. All else being equal, colder air is denser so the cylinders can take in more oxygen and fuel. Colder air is also less prone to cause engine pre-ignition thereby allowing use of tunes with more advanced timing. Both factors strongly favor cooler air for more horsepower. The goal therefore is more oxygen and fuel at the lowest possible temperature.
E85 can bring a lot to this party for boosted engines and here’s how:
Highly Oxygenated: Being 85% ethanol means that E85 is carrying along about 30% oxygen in liquid form. The remaining 70% is carbon and hydrogen which are the fuel burned (oxidized) by the oxygen during combustion. You get to spray this liquid oxygen through your carb or injectors thereby reducing the demand for oxygen from the air inlet stream. If you fuel system is adequately sized, you need less boost to stuff the cylinders with the same amount of oxygen, carbon and hydrogen.
Evaporative Cooling: Gasoline atomizes when sprayed into an engine while ethanol vaporizes. Liquids absorb tremendous amount of heat when they vaporize. For ethanol, it’s 387 BTU/lb. This latent heat of vaporization from one pound of ethanol is therefore equal to the energy required to cool a gallon of water by 46.4 degrees Fahrenheit. Brrr!
Because gasoline does not vaporize, intercoolers are used in most boosted applications as a means of reducing air inlet temperature following its compression. These intercoolers can be air to air, or liquid to air. In either case, they take up space, add weight, complexity and cost while typically reducing the effectiveness of the engine cooling system. E85 does such a good job knocking down inlet air temps that no intercooler is needed.
Higher Octane: Pump gas octane varies in the US by both grade and state. Here in Illinois, the octane of regular and premium gasoline is usually 87 and 93 respectively. In Colorado, those numbers are knocked down by 2 points to 85 and 91 octane. Ouch!
In northern states, winter blend “E85” is really E51. A higher percentage of gasoline is needed for cold starting. As such, it is a fuel that varies seasonally. Pure ethanol carries an octane rating of 110. Even winter blend E51 will be about 100 octane after being cut with low octane gasoline at the refinery. That still beats pump gas by a mile on octane. E85 is usually cheaper by the gallon, but that is an illusion as it contains less energy than a gallon of gasoline. One big issue however is availability. Every gas station has gasoline. Only a few carry E85, even here in the Corn Belt.
The higher octane of E85 allows us to either increase the compression ratio of an engine design, or put in more timing into the tune to raise horsepower. The availability issue for street cars precludes a higher compression ratio so that pump gas can still be used in a pinch. With available technology, the tune can be automatically dumbed down if the fuel sensors detect a drop in ethanol content.
Lower EGTs: Exhaust gas temperature for any fuel is strongly influenced by the air fuel ratio, boost level and spark timing. Assuming these are all set for maximum power, what do we see? Much lower EGTs running alcohol. Check out the video clip below for two similar engines. The first dyno pull is on C16 with cold water running through the intercooler. The second dyno pull is for an engine of the same size at higher boost running methanol with no water in the intercooler.
What a difference! While not exactly apples to apples, it is visually obvious that methanol fueled engine which made more power did so with far lower EGTs. As a rule, heat is the enemy of engines and glowing hot pipes are probably not the best thing to have under your hood in a street car.
The biggest factor for the vehicle is that no intercooler is required. This makes engine installation far simpler and less expensive. Big horsepower means big engine cooling requirements. Intercoolers of any kind cut into the available air for engine cooling. Not having an intercooler also frees up space and reduces weight.
Be prepared to put some of the install and fabrication savings back into the fuel system. E85 will swell the rubbers, plastics and gasket materials used in most fuel systems. It is critical that everything from the fuel tank to the injectors be E85 compatible. A vented cap is also required. It is also critical to size everything larger, given that you’ll need to use 1.3x the volume of E85 to make the same power as gasoline and you’ll probably want to make more power if you can get it. A larger stainless fuel tank would be a good idea when switching to E85 as it will address both chemical compatibility and range issues. Absolutely install a fuel sensor so that your ECU can maintain a proper air fuel ratio as fuel composition varies.
Alcohols are hydroscopic meaning that they rapidly absorb moisture. This in turn can cause corrosion problems and necessitate more frequent oil changes. While most engine oils are compatible with E85, it won’t hurt to check your brand. Change your oil immediately if it starts looking milky.
One other tip. Get a little test kit so that you can check E85 fuel composition at the pump.
Where available, E85 is a great choice for boosted engines as it should deliver more horsepower at an overall lower cost than pump gas. While there are issues, work arounds exist that can resolve or mitigate them all. It is therefore our fuel of choice whenever available.
Frequently Asked Questions
- Will I get worse gas mileage using E85? Yes you will. The drop off will depend on the alcohol content which varies seasonally down to E51 winter blend. For true E85, expect to use 30% more fuel.
- Won't that cost me more money? In a flex-fuel Ford Escape, generally yes since you are comparing against regular gasoline. With a Borowski LS turbo, the comparison is against premium grade gasoline. E85 will almost always win that contest.
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