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post #10 of (permalink) Old 04-01-2014, 09:39 AM
PSIG
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Join Date: Jan 2008
Location: Seattle, WA area
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Re: Stroker intake manifold RPM change-PSIG???

I know about those hot chicks, and the lure they have. The CC article is interesting, and I love that they included average HP numbers, but be sure to consider a few things:
  • The manifolds were not port-matched to the heads - a cripple-factor for some of them. The runners are are conical and designed to give material to port for best flow, and are relatively restricted without it. The point is that manifolds designed to be ported for racing cannot be fairly compared as-is.
  • None of them were flow-balanced. As-cast differential can run 40cfm or more from port-to-port. That's a lot of lost power, and highlights that race manifolds are not meant to be a "bolt-on" solution.
  • The awkward dual-plane still provides amazing power for it's convoluted runners, and slightly better average power than the "race-only" manifolds. Higher peak HP or TQ only means it was weaker somewhere else. Peaks are meaningless except for dyno racing and diagnostics. Averages are more useful, but must be in your useful range.
  • Another dual-plane, the dual-quad has better runner layout than the RPM, so pulls ahead in average power. Double carb cost, double setup, double failure points, but double fun. Not a fair comparison to a ported manifold, though. Gotta love the un-ported bolt-on numbers.
  • Yep, they had to throw a spacer in there, and only on one. We know why they did that, and should have done it to all if to one. Spacers always add dyno power.
So, it apples-to-oranges, but we can still see trends and factors that would apply to any engine combo. Another example - the header/exhaust combo was not specified for it's breathing/harmonic traits, so it may have helped certain combinations and hurt others. With attention to the exhaust, any one of them could have been a clearer winner.

As far as porting your own, note that head port/runner mismatch is usually solved with both grinding and filler, and this way the runner can be moved wherever you need it to match the head. One filler that works with high heat and fuels including ethyl alcohols is A-788 (aka Splash Zone) around $40/quart kit. Methanol needs a sealing coat for extended durability. Split it with a buddy or 3, as it will still be too much and shelf life is a year. Perhaps you might play with your old mis-aligned VJ while you're having fun with the SV? Nothing like some cheap real-world practice to see where things really happen on your combo.

David

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