[Nezil]

The main problem with running 100 octane is that it's really expensive. I can get it fairly locally, but at $7~8 / gallon (3.78 litres for a US gallon, not 4.54 for a UK gallon) it's quite a bit more expensive than E85.

The other thing to keep in mind is that road legal 100 octane in most states (CA and AZ too I expect) is heavily oxygenated i.e. it already has a lot of E85 in it, so it may very well be effectively the same as mixing pump 91 with E85. If it was true 100 AKI ethanol free gas, then I'd say go for it, but I doubt you can get that easily.

As ZM2 said, if you can get E85, you don't mind mixing it, and your HPFP can handle the extra flow needed, mixing up E20 to E30 might work. It didn't work for me because our base fuel is already E10, probably 90.5 rather than truly 91, and behaves, according to Halim@HCP like 87!

I'm now running 50:50 water methanal, and am able to run the 93 AKI OTS Stage 2 map without timing pull.

WMI is more expensive, and an addition think to keep an eye on, but it provides octane, cooling and fuelling. The cooling effect is so good that I'm considering going back to the stock FMIC... On a 3rd gear pull, IATs will be below ambient by the end!

I get through about a gallon of 50:50 water:meth every 2.5 tanks of street driving, and I can buy 5 gallons of 100% methanol for about $30. That's $1.20 extra per tank, so the operational cost is very low.

I am wary of octane boosters, partly because of the orange deposits, but mostly because our 91 octane pump gas is just so bad. Can we really raise it from an effective 87 up to 93 with just a small bottle of additive?

Finally, I should mention that PTF's Dzenan actually suggested I try adding Methanol to my pump gas straight in the tank. He suggested 1 gallon / tank initially, and I did think about doing that, but decided against it because I know my HPFP is already weak, and Methanol has an even lower energy density than E85...