Thread: 91 & E85 Mix

Finally found a near by station with E85.... I have half a tank of 91 Octane in my 04 Pontiac Grand Prix Supercharged. Two questions,

1. Am I ok to fill the rest of my tank with E85?

2. What's the Pro's/Con's of higher Octane?

Thanks!

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Originally Posted by Fivefingerdeathpunch

Unless you can tune for it, you won't want to do that.

E85 requires at a minimum of 30% more fuel flow compared to regular unleaded gasoline.

Even though E85 if it's actually 85% alcohol is roughly 105 octane there is a draw back (most winter blends are E50 or E60 right now). It requires larger fuel injectors for more fuel and should always be tuned for. Also you get roughly 30% less fuel mileage.

So even with a 50/50 mixture it's likely to be around E30 or E40 in the tank. Sure it's higher octane than regular 91 by a little bit but it's still something I wouldn't do unless you had a tuner.

Seen somewhere that was calculated to mix fuel to get 93 Octane but I don't know much about this Octane numbers and levels. You just educated me on some of it. Thanks

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Originally Posted by GTPpower

You can run up to e40 on a stock tune without issue. So with half a tank of non ethanol 91, you can fill up the rest of the way with e85.

The actual octane of e85 is more like 94-95. But due to its cooling effect it has on the intake, it performs similar to 110 octane.

So would this be correct?

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Here based in Cali. Not much of the 'e' Octane ha

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