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Old 12-06-2011, 09:11 AM
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chevy 454 DCR question

Ok, i'm currently planning a build for a mark IV 454 4-bolt main and i have a little problem. i've been simulating engine builds on a copy of Desktop dyno but i am unsure just how high i can take compression ratio. For your information i am planning to use forged crank/rods/pistons with either edelbrock or AFR heads oval-port heads, hydraulic flat-tappet cams(leaning towards comp-cams 11-404-4) and a garrett turbocharger with an intercooler. Here's my question: Assuming I used an oil cooler of sufficient capacity and an intercooler for the turbo, what is the maximum DCR or BMEP I should be looking at to run on pump gas. I have been looking everywhere and found not much. I have heard that it is somewhere around 8.75:1 but i just don't believe that as i know of several current engines that run in the 13:1 SCR range. Now granted that SCR and DCR are going to be different, but to drop to 8:1 from 13:1 is almost half, i don't see how an engine could do that and still idle decently and they do. My suspicion is that if i can keep the block cool on top and bottom with a solid radiator and oil cooler, and i can keep the intake air cool then I should be able to get to about 10:1 DCR or just under 200 BMEP. Am i on the right track here? I have plenty of choices on heads and pistons to change the combustion chamber size so i would rather nail down this problem BEFORE i start buying and boltin' stuff up.
That brings me to my second question, does anyone know of any online guides or the like that can help me determine how big of an intercooler i would need for an air/water style interface without becoming heat-soaked. Little help here guys.

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Old 12-06-2011, 11:47 AM
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Just a couple thoughts.

Generally a DCR of something below 9:1 is what many engine builders use as a cut off point for pump fuel (not talking E85 here), so I wouldn't argue with your figure of 8.75:1 DCR.

That said, in boosted applications there are ways to fight detonation besides lowering the CR or timing as I'm sure you're aware- water/alky injection, air-to-air or to water intercoolers, N2O cooled intercoolers, boost retard, to name a few.

To run a boosted engine at anything approaching optimum timing w/a DCR that are above what is known to cause detonation is going to require better fuel than you can buy from most pumps along w/one or more of the schemes mentioned above, I just don't see any practical way around it.

BTW, unless you actually saw an engine go together, there's no way the CR can be verified as being xx:1, IMHO. Guys have been known to exaggerate, you know... not saying anyone's pulling your chain, just sayin'.
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Old 12-06-2011, 01:02 PM
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The post above is primarily aimed at a carbed set-up. EFI and electronic engine management can increase what you can get by with- again as I'm sure you understand.
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