91 Octane build

[DirtyErnie]

Looking for tips, spitballing a rebuild with new pistons. We can get 91 octane non-oxygenated/ethanol free gas is a lot of places, so I'm thinking about high compression for 91.


I have a Hoos Racing Shell#1 cam, and a stock cam on the shelf.

What sort of compression ratio should I be looking at on either a 650cc 1st Over, or a 700cc overbore?
Thanks!

 

[ihaxs650]

Off Topic, in Kalifornia you can get 100 octane for just under $9/ bucks a gallon.

 

[TwoManyXS1Bs]

My old-school '70s thinker and rememberer seems to feel that 9.0:1 is as far as you'd want to go on 91 octane vintage blend...

 

[hotdog]

I usually aim for 9.3 - 9.7 CR, that's running 95RON here in Australia
My Evo BT is also set up @ 9.7 and I run 95RON (and sometimes 97RON) in that, I have used 91RON it in once and it detonated badly.
My 2c would be to keep it around 9.0CR as already suggested.
Running the shell #1 will also help with keeping the CR under control and minimising the detonation.

Goodluck with your build.

 

[DirtyErnie]

E85 is about all we can get around here that's over 91 (R+M)/2. What's that stuff supposed to be, 105? Same blender pumps put out E30, allegedly about 93-94 octane. My FFV F-150 gets the same mileage on that stuff as our state-mandated E10, and it's quite a lot cheaper...

... Not that I want to run any more ethanol through carbs on a street bike.

Thinking of 700cc 9.5:1 would be the easy path.