Planning a 408 build. Trying to decide on E85 vs 91 and respective compression ratio. I have one station down the street that sells E85. I already have steel fuel lines and plan on installing an electric fuel pump regardless. I typically keep my drives approx 20 miles or less. Would be 80% street and 20% track. Just trying to figure out if I go with 12+:1 using E85 only or go with 10.8:1 which allows me to use 91 if needed. I understand it is all about educating myself on the nuances of E85 and making a personal decision, just curious if there was a consensus one way or another.
If relevant:
Elevation: 6,000 (Denver)
Heads: Trick Flow 190 60cc when released in Sept
Cam: TBD FT solid
Horsepower goal: 450-500 would be nice.
I think you're gonna have trouble getting air up there as is, and you will have to run extra cylinder pressure. With aluminum heads, and a typical big street cam with a 68* ICA , you'll want to run an Scr well over 12 or 12.5 anyway.Oxygenated is kindof a natural for you
At 10.8 I don't think you'll find a cam with a small enough ICA, to not be somewhat soft on the bottom, with iron heads.
Have you run your combos thru the Dcr calculator yet?
I think the difference from sealevel to 6000 is like 30 psi in cylinder pressure. Yeah that's what I keep seeing.
Suppose you want to run at least a 230* cam to find some air up there. And a solid FT, so that could be a 268/276/110.. Installed at 108, I get an ICA of 62*..When you put that into the Wallace at 10.8/6000ft,I get; 151psi and a VP of 148. Because it's a stroker that might not be too bad.And you can run iron on that.But generally, 148 VP is about what a warmed up 367 like mine makes, and I'm not unhappy. But it's a 360. If I had a stroker, I'd expect more.
So, at 151 psi, there's quite a bit of room for improvement. At 11.3, the pressure jumps to 163, and VP to160. That's an increase in VP of 8%.And that's about the limit for 91 gas and iron heads.A VP of 160 is quite good.
But for aluminum heads and E10/15 gas you can hit 185/195 psi, and that would get you 12.4 Scr/184psi@181VP , a killer bottom end.And normal for aluminum heads. Normal meaning won't detonate on pumpgas.
I can't speak to running 12.4 at WOT at 6000ft; you'll need to talk to the builders. I can only speak to the numbers in this case. The highest I have run was 11.3. and currently at 10.9
And all this with a 268* solid Ft cam, with an ICA of 62*. If you want to run more cam, it's back to the calculator. But 12.4 is an easy build I think; flat-tops at zero deck with 5cc eyebrows,60 cc heads, and the rest in the gasket .039/8.9.
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I run a cam pretty close to that, at 900ft, in my 367 at 10.9 Scr and 175 psi.....on 87E10. I have run over 185psi on 87E10. Some guys on FABO have reported over 200psi on pumpgas; I'm assuming 91.