stock '88 t-2, have heard that because compression is lower, 93 octane is not
absolute necessity. some turbo owners run ethanol free and pre-mix with
great success. my t2 is not a daily driver and would really rather use non
ethanol and pre-mix. Any feedback, experience,recomendations,etc. would be
greatly appreciated.
Thanks, Mike

 

I'm not a 2nd Gen owner. And not certain exactly what your asking about...premixing or octane levels. But FWIW....
My car has the basic bolt-on modifications and I have no issues with 91 octane where I live. Here in the Midwest anything over 87 is going to have some ethanol, but I've never seen any ill effects from a small ethanol blend...and that's after many years. Premixing (IMO) doesn't markedly affect things. I premix at a reduced rate (1/2 oz. per gallon) WITH a working OMP. But I also have a simple boost-activated water injection system and don't worry about carbon or knock with it.
All that said, If it's not a daily, then the relatively small price at the pump for 93 isn't a big deal. While I typically feed my car 91, when I can get 93 where I live, that's my choice. If you're truly "stock" then you have an OMP and premixing at that reduced rate is great for the hard seals, but MAY have some effects on your cat and MAY contribute to some carbon fouling on your plugs over time.
RE: compression...
I'm not a big-brain, but I don't think compression ratio plays as big of a factor in a rotary's need for a higher octane fuel. It's the long shape of the combustion chamber and the larger surface area of that chamber. Add in the fact that rotaries tend toward carbon deposits because they burn a small amount of oil and it all contributes to the risk pre-ignition. Now factor in forced induction (turbocharging) and a real lack of toleration for detonation and you want to use a high octane fuel...IMO.