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Old 29th December 2018
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Skuzeee Skuzeee is offline
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Originally Posted by aswracing View Post
What compression ratio are you proposing?

Keep in mind that your hemi chambers are detonation prone. There are limits to how hard you can push the cylinder pressure. You need to match the compression ratio to the cam timing and make sure the combination stays under the detonation threshold (it can all be calculated, by the way). So if you're raising compression significantly without also changing the cams to match, tread carefully. Like I said, even taking you to 9.6:1 with the stock cams, which is what the flat top 1275 does, is going to require careful tuning, when you're talking about hemi heads.

Most high compression pistons for your heads are 10.5:1. Maybe someone makes a smaller dome, I don't know, all the ones I know about are 10.5:1. You run 10.5:1 with your stock cams and hemi chambers and well, good luck with that. It's not something we'd ever put a customer into.

Another question raised by this proposal is the value of the big bore kit as compared to it's incremental cost. If you go buy a set of high compression pistons and properly fit them to your stock cylinders, you're going to spend nearly as much as a 1250 kit and be within a couple hundred of a 1275 kit. So is the additional power that comes from one of those kits worth the incremental cost? Obviously, I'm not an unbiased party. But I've shown you what the 1250 and 1275 bring to the party, so I'll let you decide.

And finally, could you pull this off within your $1K budget?

Those are all questions I'd be asking before I went down that path. I'm not going to sit here and say it couldn't be made to work, but I'd want answers to those questions.

Sure, you could do this. I'd sure put an ignition into the mix, because you're going to need a higher rev limit if nothing else. The cams are going to move the power to the right side of the chart, and almost certainly rob from the left side in the process. Whether that's better or worse than the across the board gains from a 1275 with stock cams, well, again, I'll let you decide. Depends on what matters to you.
Thank you again, that cleared things up for me. I understood that big bore is the go-to way for gains, but I was not sure why other routes aren't considered.

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