Thread: Octane Rating 91 vs e85 etc.

Can someone explain to me what gas is better for each set up.

91 is best for?

And e85 is best for?

Can you get away with less supporting mods using e85?

I keep hearing about e85 and always asked what Octane im using or whats available, like it matters. Which I know it does, I just need more info on this is all.

Knock Retard, Dropping down pulley sizes and headers vs plogs etc.

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Originally Posted by Fivefingerdeathpunch

91-93 octane works in anything, it can make lots of power with the right setup. Supercharged or turbo doesn't much matter with the fuel type but what you can get away with can come into play sometimes.

E85 overall is better for making all out power, there is no substitute there besides C16 race fuel. You can do less "supporting" mods with E85 because of how well the fuel works at keeping cylinder temps down and knock away.

The trade off is that E85 will consume at a minimum 30% more fuel than regular unleaded gasoline, think more like 40-50% though. So if you care about fuel mileage, it's not the best option and even though the fuel is cheaper in most parts of the country you will be stopping twice as much so the savings is a wash.

Larger fuel pumps and injectors are required too and it's not something that works well in the really cold climates.

Thanks! That's exactly what I needed to hear. Will the PCM play a role in what gas I use?

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Originally Posted by Fivefingerdeathpunch

You have to tune for whatever fuel you choose to use but the stock computer can do both fuels if you know what you are doing.

It how ever can not do both fuels at the same time, it's either one or the other.

Ooh, ok. I see. Thanks

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Originally Posted by Fivefingerdeathpunch

You have to tune for whatever fuel you choose to use but the stock computer can do both fuels if you know what you are doing.

It how ever can not do both fuels at the same time, it's either one or the other.

I have an 04 Pontiac Grand Prix Supercharged and now that I've just started modding, I just found out that my Car was made for 91 Octane and I've been putting 87 in it all this time. Had me thinking for a minute that I may have been damaging my car. PCM tuned for 91 and I'm putting 87 in the tank

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Originally Posted by Scottydoggs

more octane is better. e85 has more, end of story. i cant get e85 here so ill toss in a curve ball, i run meth injection, makes your octane rating about 106 with 93 gas. bout the same as e85.

Whoa, meth injections. That's something new. Never heard of that one.

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Originally Posted by Scottydoggs

all you can do with out a tuner is run higher octane. if you got 93 or higher run that. if you got kr now, the 93 should help clear some or most of it up.

no one does a canned e85 tune, or meth tunes, they need to be in car tunes.

Ok, got it. Building knowledge!

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I run E85 and meth injection, it works good. I get about 30% worse gas mileage, sometimes a little worse, but it's been windy here lately so that is a factor for sure. I use an E85 calculator app on my phone and it's actually a little cheaper than using premium, but definitely do have to fill up more, so the trade off for me is time spent at the pump. I fill up every day as I drive 170 miles per day. the savings for using E85 is only like .03 cents per mile, but since the car makes more power, that's my justification.