compression ratio questions

[IPD]

so your consensus is that lower than 8:1 is diminishing returns with pump gas & air-cooled intercooler?

[KeithMac]

If you could push enough boost to warrant 7:1 or 6:1 CR pistons it would be a lag monster on pump and nearly undrivable off boost I would think?.

I like my M20 mixes, 20% Methanol in the tank allowing me to run more ignition advance than straight petrol.

[IPD]

that's why i asked. i'd like to get the full story. it's an obvious continuum, and what happens on both extremes is of interest to me. somewhere around the middle has to be a range of acceptable performance. my gut instinct is that 7.5:1 is probaby as easy of an adjustment from 8:1 as 8.5:1 is. but i'd really like to hear details.

p.s.
thanks again for the article. now i have something definitive to shove in the face of people who swear up and down that ethanol is shit.

[Ray Pampena]

Ray, what if you remove pump gas from the equation and only use race gas or ethanol? Other platforms (porsche, supra, dsms) seem to have good results with higher comp (9 to 11:1) with turbos and significant boost. What are your thoughts if you are removing octane limitation?

it all works out to be the same on gasoline. power before spark knock is reduced even on race gas. think of things in extremes when comparing boost level and compression ie. 10:1 and 9psi vs 8:1 and say 15psi... which makes more power on the same gas before knock 13:1 and no boost? or, 7:1 and 25psi?

e85 seems to run better with higher compression and boost because of its resistance to knock

[familyMAN]

it all works out to be the same on gasoline. power before spark knock is reduced even on race gas. think of things in extremes when comparing boost level and compression ie. 10:1 and 9psi vs 8:1 and say 15psi... which makes more power on the same gas before knock 13:1 and no boost? or, 7:1 and 25psi?

e85 seems to run better with higher compression and boost because of its resistance to knock

Thanks for the reply Ray. I am in the parts gathering phase and was thinking of 9:1 Mahle pistons for an E85 only, 16G build. Not really wild CR like some of the DSM and Supra ethanol builds.