Octane and Ethanol

This question has become ever more popular...I probably get it several times a week and it involves octane, ethanol, and how states require fuel to be mixed. Before I get too involved, let me first explain what "octane" really is. The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, you get detonation. Lower-octane gas (like 87-octane gasoline) can handle the least amount of compression before igniting where higher octane like 93, can handle more compression, which is why we run it in high performance engines. Keep in mind the effective compression limit for 93 octane is very close to 10.5:1 CR (at sea level). To make it as simple as possible, the higher the octane, the "less flammable" the fuel.

So here's the scoop:

We already know we have E-85 fuels now which is a mix of 85% ethanol and 15% gasoline but let's consider the much older alternative which is E-10...10% ethanol and 90% gasoline.

Ethanol is currently blended into about 70% of US gasoline, the majority as the E10 blend. Each state determines whether gasoline needs to be labeled if containing ethanol, so if you're in an area where labeling is voluntary or not required, you wont always know if the gasoline contains ethanol. Ethanol blends are offered extensively throughout the Midwest and are becoming more and more widely available from coast to coast. Because pure ethanol has an octane rating of 113, adding 10% ethanol to gasoline raises the finished fuel's octane rating by 2 or 3 points, improving the fuel's performance. Unfortunately, if you live in a state that doesn't require labeling, you don't know if you are getting a TRUE 93 after ethanol, or 93 plus 2-3 giving you 95-96 octane.

The problem is that if your bike is tuned on 93 octane (no ethanol) and all of a sudden you use E-10, you may feel as if you've lost power. You have, but not really...it's not because it's "bad gas", it's because the fuel is less flammable. This can be worked out with proper ignition timing adjustments. Call your local clean air force, energy association, etc and ask if your state is one that requires ethanol blending to be posted at the pump. If they do and it's posted as 93, rock on. If they dont and they tell you the posted octane is before E-10 is added, you can be more aggressive with igntion timing and pick up more performance than those with a true 93.....so don't sweat it....give it what it wants. I feel it important to note this is why "universal fit all" timing tables don't always work and can be another factor as to why identical builds can produce mildly different dyno results. A 2-3 octane jump can be worth a few degrees of timing.

Side note: altitude plays into this as well but we've already talked about that on the techgroup...so I won't go there. Camshaft selection also has a HUGE MONSTER affect on this too...that's why Head Quarters is here to help you out ;)

E20, E30, or E40 is already under development and testing so be ready for it.

Happy Motoring!
Kevin Baxter