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2012 OBM Coupe, 6A, mostly stock
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Discussion Starter · #1 ·
This is my second forced induction car, however my V2 is the first I'm considering modding. It's essentially a daily in the summer, so I'm hesitant to go very extreme with it.

As I read through the forums there seem to be some very low hanging fruit with a simple pulley swap, a colder thermostat, and maybe a heat exchanger upgrade.

I feel like my limiting factor will be fuel...or rather the available octane.
I currently live in Nebraska. 91 is widely available, 93 is available at a handful of stations, and E85, in the Cornhusker state, is obviously pretty ubiquitous.

From what I've gathered, the 100+ octane of E85 plus the cooling effect of evaporation of the alcohol allows for more extreme levels of boost and tuning...at the cost of roughly 50% of the mileage one would get with either 91 or 93, and so the cost per mile at $2.29 a gal vs 93 at $3.64 a gallon or 91 at $3.14 a gallon quickly exceeds either gasoline blend. Additionally I'd need to buy larger injectors, and an E85 conversion kit.

Faced with that, 91 or 93 remain. If I was going to live in Nebraska for the rest of my life, I'd gear things towards 93 and on the off chance I had to run 91 I'd just keep my foot out of it. I'm also military, and have a high chance of being stationed in 91 only Cali.

So...How far can one go with the limitation of 91 octane fuel? I'm sure the tune is an essential part of it, but in terms of hard parts, what's the point of declining returns?

Does upping to 93 move this limit out further appreciatively or is it all in the tune?

Thanks in advance!
 

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2012 OBM Coupe, 6A, mostly stock
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8 Posts
Discussion Starter · #3 ·
Close to 700 rwhp on 91 ok stock fuel pumps…approx.


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Jeebus! Nothing to worry about then. Thanks!
 

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Also, just to be clear, you need larger fuel injectors with even a mild upper pulley swap on 91 octane. So the only additional cost of E85 is the flex fuel sensor and flex fuel tune.

If you do catless headers, the ethanol is worth it just for the improved smell over gasoline.

It’s also only about a 33% hit to fuel economy, not 50%.


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Close to 700 rwhp on 91 ok stock fuel pumps…approx.


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that would be a pretty involved build though (heads/ cam), obtainable with meth injection
 

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91 and 93 E10 will have the same fuel demand but 93 can make more power due to the extra octane. E85 needs more pump and injector but larger gains are possible. As mentioned 700whp or so can be done with E10 and stock CTSV fuel pumps.
 

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2012 OBM Coupe, 6A, mostly stock
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8 Posts
Discussion Starter · #8 ·
Thanks all! I guess what I'm really wondering is what the order is of limiting factors with a stock car. I had assumed one overall factor would be the fuel, but even with 91 the potential is beyond where I'll be wanting to go.

What's the typical trail of the mod creep? I'll start another post over in the engine forum so as to keep things tidy in here.
 

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If you look through all the builds it’s quite obvious. I suggest read more than write and you will find your answers.


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