slant six MPG build e 85

well my figuring was by using e85 i could take advantage of the extra octane to make up for the lost economy (ie lose i belive 27% thermal energy but make up by have a cr to make up for some losses) also was hoping by building a more effiecient burning engine i could keep rpms lower ( will be running a OD) and further help mpg.

i know its a horrible comparison but there is a honda prelude in town running 11-1 and 8psi on e 85. i was under the assumption i may be able to do the same or a little lower( i understand the head on the honda is a better design) and we only have 1 station currently with e85 and the owner guarantees its within 5+/-

and i was figuring the 170 would have been a better choice due to rpm? so you could build a high horsepower engine and just keep the rpm low when just driving? dan what do you think would be a good number for hp? i know you have a ton of experiance with the s6.

thanks for the input guys