I think the bottom line is this: If you want to squeeze every last drop of power out of the setup then go with E85, because it's going to work better for that reason. If you can sacrifice some hp/tq for the peace of mind that readily available pumpgas will give you, then keep it 9:1. Or if you have a hp/tq goal in mind, then get a larger SC on 91oct at the lower CR for the same results.

I was trying my best to max out the 16g setup I had on my Talon, so I kept E85 in the tank 99% of the time, and frankly I thought pumpgas was a total bore when I was forced to switch back, because max on 91oct was very different from max on E85. When I turbo my Miata, I'm going to go with pumpgas because I'm not trying to max out the turbo, and I can get everything I want on 91oct. (famous last words)

 

Look into restrictors for the Rotrex. If it's possible to reduce the boost to whatever you want by swapping in a smaller one, why not try? If you have to fill up with 91, just put in a 60% restrictor with a couple hose clamps.

11.5:1 would be very efficient. You'd make more power everywhere, but the tune has to be near perfect. That's the major factor here.

 

The compression ratio isn't the only factor. Quality of fuel and tune complete the triangle. The Rotrex loves compression. OGK motor is 11:1 with a C30-74, (milled down Supertech 11.5:1's and chamber work). Oscar has built a bunch of race set ups for other cars using high base compression. If you are using E85 100% of the time, I'd go 11.0:1

 

+1 on getting a drum,easy access and save money.

 

how much track use will the car see ? the more track use it sees, more conservative I would be on compression. but if it a street setup, I say go for it !!

but if it is a track setup. how do you plan to bring enough E85 to drive to track and back, plus track time ? if you are towing, no problem. otherwise you need to think about it carefully.

yes, I do run Rotrex and E85. love it, but again I have stock engine.

 

I want to see it, so you should do it.