Exhaust port/ manifold match

[Steve D.]

From previous threads, I have seen that port matching on the exhaust side is not normally recommended. The exhaust ports on my 462 heads are essentially square, 1.36" on a side. The openings on my stock exhaust manifold are also essentially square, 1.31" on a side. This is the reverse of the situation where header openings are bigger than exhaust ports. In this situation does t******* the manifold opening to match the exaust port make sense? I realize that for a recreational street engine this is splitting hairs, but I'm just curious about the mechanics of it.

Steve

[Duke W.]

Re: Exhaust port/ manifold match

If you are looking to maximize power, I recommend matching them.

Duke

[Dave Suesz]

Ideally, the manifold

should be 1/16" bigger all the way around for maximum flow. It's not much, but enough that you'll probably be able to tell the difference afterward.

SB Fords benefit tremendusly from this, the outlets on stock iron 289/302 heads were terribly restrictive, even though the 289HP manifolds were pretty good, the 289HP used the same small sand core as the 289 2V.

[Duke W.]

Re: Ideally, the manifold

I don't buy that the manifold openings should be bigger, but they should not overhang the edge of the head port opening.

Duke

[Dave Suesz]

Well, the 1/16" oversize

assures that, unless somehow you can *guarantee* perfect alignment of the manifold. I am told this slight enlargment of the manifold side is common practice with port matching, and it has certainly worked for me.

Typically, I have done SB Fords, and the head outlets start WAY smaller than the manifold inlets, so it's only a question of not going too far.