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I am interested in lowering the compression on my 69 Mustang for blower. I have heard the following will work:

Install thicker head gasket. Will a thicker or double head gasket work. Which is smarter? How thick should it be to significantally lower the ratio. What is a good source?

Using 302 rods in a 351 Winsor. Is this smart? How do I get this to work with the Windsor crank and pistons?
 

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what compression do you have now? thicker gasket will not work. best is to have the right pistons installed.. i did and i love the power.. keep the compression down to 7 - 8 to 1 so you can use pump gas.. i went with 9 and i have to run 100 octane for it to run right....


enjoy the pile of horsepower
 

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low compression

I am presuming you are running a 351W, as you didnt specify whether you have a W or C block, with your referance to the 302 stuff in a 351.

302 rods will not work in a 351. They have a smaller rod bearing size, and are .80" shorter.

Running 302 pistons in a 351 could be done but you will be dropping the compression way low. The 351 piston has a deck height of 1.77" vs. 1.604" with the 302. Not sure what that would do but you would probably wind up with a compression of around 5-6:1. Be good for about 30 lb of boost and nitromethane though; after you build the bottom end up.
Were I you, I would contact the various outfits like Paxton and Vortec, and see what they recommend, concerning your present compression ratio and adding a supercharger.

I concur with going with lower compression pistons, rather than using extra thick head gaskets.
Your stock compression is 9.5:1 and you could run a boost of 5-6 psi, without any serious problems, I would think.
Your engine has an advertised compression of 120 PSI. While your compression should be in that area, the actual compression ratio may well be down around 8.8-9:1 compression, as quite often pulling the heads and doing all the measurements often prove in production engines, The advertised CR quite often is somewhat higher than the actual.
Since this is a 69 engine, and probably got boo coo miles on it, I think I would entertain the idea of rebuilding it and doing it right, from the ground up.

In 64, I saw a road and dyno test done in a 2 bbl 289 in a 64 Comet, running stock compression of 9:1. The article was about putting a Paxton centrifical supercharger on it. I dont remember what the boost was, etc, but the performance figures were impressive, even with the 2 bbl carb. They made no internal changes in the engine, running stock pistons.

Camaroman is hot on huffers, maybe he will come in on this.
 

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Running a unnecesseraly thick head gasket in order drop compression is a bad idea no matter what your goals are. You want to obatin proper quench (area from top of piston to deck of head), and using a thick head gasket will throw this off. Depending on what compression you have now, you will probably be best off buying a new set of pistons like everyone has said. I would recommend an intercooled procharger as far as which super charger to use. They have a lot of really good info in their catalog on their website, I would recommend reading all of the technical stuff if you have the patience, it is all really good information.

http://www.procharger.com/pdf/Chevy.Prod.bb.pdf


Adam
 
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