I'm going to have a mail order stroker shortblock built but I already have a set of ported heads. I assume my cam will be a bit too small for the larger motor (222/230, .533/.544, 112 lsa). I'd like to have a cam selected and installed by the builder but I'm not sure what info I can give via phone that can get me going in the right direction. I've seen it mentioned quite a bit on these boards that the cam has to be matched to the heads but I have no idea what this entails. Can this be done by just knowing the flow #s for a particular set of heads? When building a motor, is it necessary for the builder to have the heads in hand for the proper cam to be selected? What factors are there to be considered when trying to pick the proper cam?

 

Knowing flow numbers, intake port volume, and chamber size all are important. For example, if your have heads with small intake poor and relatively poor flow, it makes no sense to get a huge cam with a narrow LSA that will only work well at high rpm. Similarly, chamber size is a major determinate of CR. If you have very small chmabers and are using flat top pistons, your CR will be high which will allow you to sucessfully use a cam with a late IVC (iow, a cam a long intake duration). If your heads stop flowing at 0.500" lift, getting a cam with huge lift wouldn't make much sense. There are a number of other examples.

The most direct way in which head characteristics impact ideal cam specs is the exhaust v. intake flow. LT1 heads usually have relatively weak exhaust flow. This necessitates a "dual pattern" cam, where exhaust duration is greater than the intake. Knowing you head flow numbers, especially in the intermediate lift range, will directly influence how wide you want the split betweeen intake and exhaust duration to be.

This just touches the surface, but I gotta go. Hopefully it was of some use and maybe others will chime in as well.

Rich Krause

 

Thanks Rich, that was very informative. Unfortunately when I ordered the heads/cam package, the only information given to me was the head flow #s. I actually had to have that info mailed to me. The chambers were done but I couldn't begin to tell you what cc they would be now. I assume since the factory chambers are 54cc mine should be around 59-63cc now. I didn't have the heads shaved to bump compression I assume they just machined to achieve flatness.