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Joined: Apr 2003
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From: columbia
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I know I have asked similar questions befors but I want to be sure. I'm use ing a comp 268H on my 351m I plan on makeing it a 400. Useing stock 4bbl heads I want to boost the cpr a little to run this cam should I use aftermarket pistons or stock 400 pistons? Are there better heads for these engines that I can get from a salvage yard? If I use aftermarket pistons what brand would be the cheapest but with good quality? how much would you guys recomend milling from the heads and block if I use stock 400 pistons? basically I want to know how I need to build the topend of a 351M with a comp 268h,Holly 4bbl 600cfm, Edelbrock performer400 4bbl intake and dynomax headers. Thanks for any help.
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Joined: Aug 2001
Posts: 4,270
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From: Delaware
If you use a 400 crank and bore +0.030, you can use a Silvolite 1160 piston with a 1.63 CH and 10cc dish with Aussie 2V heads(58-63cc) with the 268H cam. You can also use 351C-4V closed chamber heads(62.8cc), but that requires more modification.
If you use the same crank and bore and a Badger/Dynagear/Ohio/Ertel flattoop piston(1.64 CH) and 3cc valve relief, you should use a little more cam.
The Comp Cams 268H has an IVC of 64 degrees ABDC. I am using a Crane H278-2, dual pattern cam with IVC of 72 degrees ABDC. These heads prefer dual pattern cams. I think that Comp Cams has a 275DEH that is similar.
If you bore less than +0.030 you will still be OK, but these numbers should be checked if you bore more than that.
If you use the same crank and bore and a Badger/Dynagear/Ohio/Ertel flattoop piston(1.64 CH) and 3cc valve relief, you should use a little more cam.
The Comp Cams 268H has an IVC of 64 degrees ABDC. I am using a Crane H278-2, dual pattern cam with IVC of 72 degrees ABDC. These heads prefer dual pattern cams. I think that Comp Cams has a 275DEH that is similar.
If you bore less than +0.030 you will still be OK, but these numbers should be checked if you bore more than that.
