Quote:
Originally Posted by rhipsher
I'm doing the same thing to my 90 as we speak. I thought the magic number to shoot for was 36mm but everybody seems to be going beyond that. Your going with 36.5mm and pete did 37+. Now is going bigger than 36mm only if your porting the heads also or not? I want to make sure I get the maximum benifit and not over look something that I should have done while it was apart. I'm still learning to.
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The physics in me would like to say it was a measurement derived from some in-depth analysis. But, honestly, 36.5mm (in my case) was more of a byproduct of the sanding/finishing the 36mm ports than it was a deliberate attempt at 36.5; coupled with the fact that when I asked Marc H about finished size and the "magic" 36mm diameter, Marc (and others) indicated to me that a little more is perhaps better, especially in the plenum. ("Can't be too big", is what I believe I heard him say, regarding the plenum.) And, since I eventually intend to port the heads too, and taking notes on "Quick Pete's" (beautiful) porting, I felt 36.5 was a good place to be. We'll see when I get to a dyno!
Just my observations: As for any significant difference in top end only vs. top end where the heads are also ported, it appears that several that have ported heads (and cams?) also have removed the divider between the runners in the plenum. Is that the result of some secret science known only to those with ported heads, or just the result of wringing out every bit of HP, i.e., "more is better"? It would appear, however, there is a significant difference between the porting done for a stock bottom 350 vs. porting done for say a 441! Can we say "Siamese"?
Bottom line: I haven't seen or talked to anyone indicating there is a big distinction between the finished diameters for top-end porting only vs. top end where heads are also ported, except to Siamese the plenum
on a 350 cid bottom. However, there is a significant difference in the convention among tuners with regard to the IH to head transition: some being very short, and some as long as possible. I went with the latter, and we'll see what the dyno says about that!
P.