I did a search, but found absolutely nothing trying multiple search methods as well as Google. A lot of E85 information, but not much on E10.

So, up here in WI, the two major cities Madison and Milwaukee have up to 10% Ethanol added to our gas (E10). Some stations have ethanol in their 93 octane fuel, and others don't. Is this common around the US? For those on pump gas, are you forced to run on E10?

My main question is...since adding 10% ethanol to gasoline theoretically causes a ~3.5% decrease in BTU's, yet increases the octane rating (although still only rated at 93 octane ?), what should I do when tuning my car? Should I shoot for lower target AFR's, like high 10's instead of low 11's towards peak boost? Should I be able to advance my timing a little more than I would on 100% gasoline, or does the 93 octane rating truly mean 93 octane? (which would mean they would have to use crappier gasoline to compensate for the octane increase of the ethanol)

Or does 10% ethanol make such a little impact that I shouldn't have to tune differently? I'm thinking this must be the case, since I don't see this issues discussed really at all.

If this has been discussed many times before, please point me there and I can close this thread.

 

assuming its a RON rated fuel (which it has to be), it still 93 octane so it has the same resistance to knock.

tune the same.

 

I use it somtimes. I have a station near by thats sell 93 octane with 10% ethanol . Its 91 octane and the 10% raises it up to 93 . The best octane gas with out it is 92 octane found only at BP Stations . Most stations here have 91 octane .