High Compression Engine Build - Page 5

Migsubishi · Oct 15, 2009, 02:14 PM

It all comes back down to the fuel used, no one would want to run high compression using pump gas and high boost. To run high compression and high boost would require high octane so that the boost pressure is not affected allowing more power to be made as long as the head stays on the block right?

I figure with the use of E100 that 12.2:1 compression can be easily used with boost pressures up to 40psi on lets say a 35r based turbo. I believe at around 40psi or under is where one would want to stay on a smaller framed turbo for longevity.

Now for these guys that are running methanol like M5 and better, well it would seem that boost really would no longer be a limiting factor wouldn't you say?

Not to sure but I'm trying to get all the knowledge possible on this. The only ones I know that have tried this is Spyros and others across seas that are making unbelievable power with little boost numbers.

Ted B · Oct 15, 2009, 02:26 PM

Simply put, greater working pressures tend to upset a fuel's stability (a cause of detonation), and the octane rating is a fuel's ability to resist detonation. That being said, there is a limit to what a fuel of a given octane will withstand.

What works for a given combination depends upon a number of factors, such as the efficiency of the turbo, the design of the piston and combustion chamber, valve timing, etc., and so forth. Will E100 work with 12.2:1 SCR and a large turbo at 40psi? Maybe so. One either has to consider what's been done by others and how successful that appears, or, be willing to venture into the unknown and discover the answer himself. It's a question that isn't easy to resolve with math.

In short, just remember that boost trumps SCR. That being said, where there is a question, I'd prefer to stay in a 'safe area' with the SCR and be generous with the boost.

As for making better power with lesser boost, that is probably more so a function of volumetric efficiency than SCR. There is a reason why Hondas with 340cfm heads seem to make big power with relatively little effort.