2000 Chrysler Voyager flex fuel (3.3 ltr. short wheel base)
 

I'm driving gently. Coasting some Pulse and glide but stay in gear. this mini van does better than the vehicle it replaced ('93 Chevy Caprice Classic Wagon w/ 5.7 ltr). I have a question: Since this is a flex fuel car, does ECM detect higher octane ratings than 87, since E85 is rated at 105 octane IIRC? Am i getting the full use of 93 oct gas if i use it in this vehicle? Also i am am going to try to find E85 in my area (metro Pittsburgh) and possibly try it on a road trip. Also what would be the best mix of E85 and E10 gas to boost octane and get best mileage?

I actually think that your best mileage will come from gas that has no ethanol in it whatsoever. the benefit from higher octane is achieved with higher compression ratios. if you had a car built for just E85 it would probably get pretty good mileage but since it is set up for both (the flex fuel thing) I think it just retards and advances the timing according to the fuel.

many of us complain on here about E10 and how it has negatively affected our mileage. there was one user who actually used E85 and talked about the equivalent cost since it was cheaper at the time (not sure about now) but he was seeing less efficiency but with the cheaper cost was still netting a gain monetarily.

the debate over 87 octane vs 93 is one that wages on. some say you see no advantages where as others have seen advantages. not just in mileage but other areas. most of this argument is opinion based.

generally speaking, the rule of thumb around here is the less ethanol the better.

I may not speak for everyone but that is what I have gathered from past posts on this subject. I personally stay away from E10 as much as possible

:thumbup: It's great that you're getting good results!

I don't think increased octane will increase your fuel economy. However, you can certainly try it and see. Just be sure to do long-term A-B-A testing before you declare it a success or failure. It's easy enough to do in this case.

I'd be interested to find out how you do on E85 but I suspect that it will be as BEEF says, you will lose fuel economy with it. Of course, if you lose 20% of your MPG but the E85 costs you 50% less then you come out ahead on cost, and if you're in it for environmentalism then it's probably a win too.

here is some info from wikipedia (I know, take it or leave it)

but anyway, they say some interesting things about regular gas vs E85. it also claims that the octane rating printed on most E85 pumps is wrong. there again, it is wiki so take it or leave it on that one.

https://en.wikipedia.org/wiki/E85

the interesting part for me was in the "COMPARISON TO REGULAR GASOLINE" section

Idle half-baked musing: Since E85's octane is so much higher and would be optimally used with higher compression, I wonder if a diesel engine block/bottom end/heads could be combined with a gas engine's fuel and ignition systems to run E85 with mostly off-the-shelf parts (don't forget to drill some spark plug holes in the head)...how much more compression does E85 need to be most efficient?

doing a search, several people are talking in the 12-14:1 range. a few have mentioned 18:1.

I think the diesels run in the neighborhood of 17:1 or so, though they are trubo charged and develop around 30psi of boost as well.

if you did do this to a car though, you would only be able to run the E85 in it and be limited to it. availabilty becomes an issue then.