Quote:
Originally Posted by dwx
E85 doesn't really have an octane equivalent. It will make as much power and be almost as knock resistant as running 116+ octane gas like VP Import or Q16, and is much much cheaper. You just need the right pump/injectors/etc. since you will be using more fuel with E85. There is a reason the highest HP drag cars run on pure methanol and not gasoline.
I would never run a 335 or turbo over 12PSI on anything but E50+ built engine or not.
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That does have a good deal of merit, but the "safe boost limit" I think is still vague. We've installed and tuned a bunch of kraftwerks C38 kits which spin to 15 psi. No issues on them so far, many of which run pump gas. I've had several customers overboost to 17+ psi on bad wastegate turbo setups, all have lived with our failsafe using reduced timings.
But if you were to ask me two years ago what the safe boost level is, I'd probably say 7 psi then. What we're finding is that with the DI system at 17 psi and pump gas on the 12.5:1 CR we're running about the same ignition timing that we ran on the 10.5:1 MX5s at 9 psi. So that tells me we have room to go before autoignition. So we can keep cranking the boost up and do fine by retarding the timing to keep the pressure down on the ring lands and the rods/bearings. If I didn't think that was the case I wouldn't have run this on pump gas, but as is the case we did fine through several WOT runs in 4th gear.
That is not to say I would recommend it, but I think it can be done. With e40 and up it is a completely different animal though, and on e70+ we can hit the same timings we were running on the 210 kit at 12 psi. So the motor definitely can take it on e85.
Another very important point is that this is a supercharger. If you want to run 10 psi on pump and 17 psi on e85, it is as simple as making a map mode that limits throttle with EcuTek. That is a VERY effective way to control boost, and we've used it on poorly put together turbo systems that creep. Add in as much valve overlap as you can to spit fresh air out, and then close the throttle/kill ignition timing. Lots of backend work, but completely transparent to the driver. Simply a low/high power map when the fuel is right.