Running my bike on E85 (Ethanol)...How much more power would I get?

[NikonsAndVStroms]

Originally Posted by Skippii

I understand that.
What I am trying to understand, is why these guys are running a fuel with less energy, keeping the airflow, compression, and timing the same, and getting 10-20% more power, while you guys here are saying it won't work for me.

Here's an easy way to think about it, take 87 octane gas versus 93 octane gas. In this comparison if you burn 93 and engine built for 87 there will be no gain. But it does allow for higher compression/more advanced timing which equals more power.

With E85, as mentioned before you get less power per unit. So the fuel consumption is going up, but then you do get additional octane.

Let's call 87 A 93 B and that added compression/timing P, and for ethanol corrected for a the greater amounts needed for the engine (E)

so A=B but A< B +P

Now with A=E, you're still not getting any additional power here, even at the larger amounts of ethanol, you're still at the same amount of potential energy.
but.....

A and obviously with the higher octane rating P Can be higher with ethanol than with regular high test, so:
A< E+ P

Which brings us to the fact that most of what ethanol is doing is giving you that higher octane rating (there is a slight amount of cooling but let's forget about that for second)

Now this sounds like a fun project, but also not a easy one. So if all your looking for is just the performance, it's probably a lot more cost-effective and time efficient to just set the bike up to run on race gas. I'm guessing even at the huge prices for it right now, especially on the ninja 250 you would need MANY tanks to come close to the cost/frustrations of making an E85 fuel system

[shovelstrokeed]

The probable short answer is that they are not getting 10-20% power gain unless the engine has been modified to take advantage of the higher octane rating of the fuel, or their engines were running poorly (detonation) to begin with and the higher octane and different burn characteristics took them out of that zone.

The limiting factor on engine power is the amount of oxygen you can get into the engine, not the amount or type of fuel, Nitromethane being an exception as it releases free oxygen when burned. Alcohol fuels really don't do that even though there is an OH component. They do provide some small benefit in that their latent heat of vaporization will allow the intake charge to be cooler and therefore more dense (more oxygen to burn). This allows the engine to realize an increase in Volumetric Efficiency. An engine modified to take advantage of the higher octane (more compression) will also operate at a higher Thermal Efficiency which is where the work comes from.

An engine designed to run on gasoline (87-93 motor octane) and run unmodifed will not see any but the smallest gain in power, and quite possibly a net loss of power, from running a higher octane fuel be it 115 octane race gas or 116 octane straight ethanol.

To get more power from the motor, you have to get more O2 into the motor. It is an air pump, nothing more, nothing less. Raising the Thermal Efficiency, usually via an increase in compression ratio, will realize some gains. Raising the volumetric Efficiency via cam timing changes and cylinder head porting is still the best way to gain power.

In fact, that is probably the best/cheapest course for you. Higher compression pistons, hotter cams (longer duration and lift) and some money thrown at a knowlegeable cylinder head porter. Use a higher octane race gasoline and you will be ahead of the game both in $$$$$ and HP. Do make your cylinder head guy aware of the parameters such as compression ratio and cam timing. He needs to know that stuff or you may wind up spending more money matching cams to his work. Big bumps in the tops of pistons can play hell with flame travel and burning efficiency as well as scavenging the engine on the overlap stroke so go easy there. Again, a knowledgeable porter can help here with combustion chamber shaping.