@dlearl476 posted:My Spyder and Ducati are both tuned to run on E-Free.
@Stan Galat posted:I feel like I'm always swimming upstream on this topic, but I'll never understand why guys want to run fuel that is not readily available everywhere in the country (or at least in the part of the country you might drive). The last place I want to be is with an empty tank, sitting in front of a pump which only has a fuel I can't use.
I think we're approaching this from two different perspectives.
Let's assume you have an analog distributor and carbs, and everything is set up perfectly. Let's assume you built the engine to run right on the hairy edge (but still on the right side) of pre-ignition with E10 93. The engine can run an optimal ignition curve for the setup, but any more timing or compression and it'll knock. The engine may very well suffer pre-ignition running E-free 93 unless timing is pulled out of it, in which case the gains from the increased BTU content of the fuel is offset by the less than optimal state of tune.
Now, let's assume that the engine was built with a safety margin built in (as the vast majority of engines are). If the compression is a half-point less than optimal, using the E-free gas is the better option, because of the increased BTU content of the fuel.
I 've tended to push the limits with compression, because compression is free power. Most engines are not built this way, but modern EFI engines are-- and compensate with knock sensors and modified ignition curves for different fuels.
If you are running with this safety margin built in (less than 100% optimal static compression ratio), then running higher octane fuel won't make it run any better (which was the point of this thread before it became a holy war). Running a fuel with a higher BTU content will definitely make it run better. This is your perspective, and I respect it.
My perspective is that E10 91/93 fuel is available at pretty much every pump in the USA. I feel fine running that extra half-point of compression and not having to look around for special fuel. I understand I'll need to change my rubber bits more frequently, but there are additives I can use that help. If I ran an engine with less compression, I'd use the E-free fuel if I could find it, but I'm not always guaranteed I'll be able to.
It's all in the set-up.