Compression ratio - Ford Mustang Forum
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post #1 of 4 (permalink) Old 11-04-2008 Thread Starter
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Compression ratio

I have a 2003 gt and am looking at the 2.6L kenne bell. it says when running 15-20 psi i need to have a 8-8.5 compression ratio. now in order to get that is it all in the pistons or do the heads play a part in that. i am looking at the stage 2 heads from patriot and a set of cams from comp but still undecided about the rotating assembly for the bottom end i need some help with getting that ratio down any help is greatful i have looked at lovernois for the bottom end but their ratio is saying 9:1 can someone plz help?

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post #2 of 4 (permalink) Old 11-04-2008
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The cylinder heads do play a part in compression, as their combustion chamber volume is part of the calculation. You can find good calculators online to help you make your decision.

I'd need someone to verify, but I seem to recall that the 2003 GT motors come with a 18cc dish piston and come in at around 9 and half compression. If you can swap to a deeper dish (like 23 or 24), your compression should drop to around 8 and a half, but that's assuming stock heads. I think the stock PI heads have a combustion chamber volume of 42cc, so if your new heads have more, your compression will drop a bit just from that.

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post #3 of 4 (permalink) Old 11-05-2008
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The heads play a big part in the compression ratio, so does the shape and height of the pistons, and the amount the block is bored over stock. When you bore an engine it raises the compression ratio. There are no shortage of piston choices, just make sure you get good forged ones and good rods. Your best bet is to speak with a good machinist who has a lot of experience with modular engines and plan the build carefully, 15-20psi is going to make a lot of power, I would guess easily over 700 to the crank so you want to make sure you have the right combo to handle it and last. I've had great experience with JE ultralight pistons, but not in a modular and I don't even know what they have available for them.

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post #4 of 4 (permalink) Old 11-05-2008
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JE and Manley are the two piston brands I would trust on a high boost build like this.

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