Can a stock rx7 run e85 without any changes to the car? If not what are some changes you would have to do?

 

NO!
you would need to retune the fuel maps and add a ton of fuel across the board.
and make sure that your fuel system can handle the E85 without falling apart.

 

You would have to totally re-do the fuel system to handle e-85. It is corrosive to many of the components of the fuel system.
Not to mention it has much higher octane and lower relative power, so your car would be slower and get much worse gas milage. You would end up spending more per mile than with regular gasoline.

 

Same advice for just about any engine:

- You'd need the ECU reprogramed, or run an aftermarket ECU. Fuel lines, gaskets, o-rings, and pump would need to handle the more corrosive fuel.

- To get decent HP & fuel economy, you'd need to run higher compression rotors to take advantage of the higher octane rating. Refinements to the intake, exhaust, headers, & ports would also help.

 

This isn't 100% true. First, since E85 has a higher oct, you can run more boost on a turbo car. Yes, you need to add more fuel, but consider that E85 is cheaper. Here's a decent article:

http://www.turbomustangs.com/techarticles/e85dyno.php

 

He has an NA, so it needs the lowest octane possible. Ethanol has less inherent energy than gasoline, which is one of the reasons you have to add fuel. From what I have read, you can expect 25-30% worse fuel economy running on E-85. I would think this might be even worse on an NA rotary since they like such low octane fuel. Since, around here at least, E-85 is only around 15% cheaper than regular gas (1.79 for E-85, 2.09 for regular at the same gas station) it just doesn't make economical sense. For reference, 93 octane at the same station was 2.24, so it makes more sense for a turbo car.

If I had a turbo rotary, I would be experimenting with alcohol injection using E-85 instead of methonol, in a similar fashon to what BDC is doing with using 70% premium, 30% methonol under boost. I'm curious about how that would work.
Edit: According to that article, you only see a 10-15% drop in fuel economy. Either way, it gets worse milage. If you live in Cali and have ***-raping gas prices, like in that article, then it is of a greater economic benefit.
Problem #2 is how the engine would handle it. According to Mazda, you can only use up to 10% ethonol fuels in a rotary, but I have no idea how accurate that is.

 

here is another thread that is on the mazdatruckin.com forum on the same topic..
http://www.mazdatruckin.com/cgi-bin...=9;t=942;hl=e85