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Originally Posted by
5speed
I use to follow the theory, bigger is better, but since I have measured the ports and factory intake manifolds, they are more than adequate flow wise.
As some have pointed out, the factory intake manifold does not flow equally across all four runners. Number 4 runner has the largest csa(cross section)follow by #1, while #2 and #3 are about the same. Runner 4 and 1 have larger csa than the port entrance, while 2 and 3 are the same.
I've already dyno tested the factory intake, versus ported factory, and O2 VE manifold. The factory piece was the winner. It tied with the ported manifold for hp but was better in the low and midrange. The O2 loss power everywhere with it bigger runners and plenum.
The factory intake manifold is not the bottleneck. It's not because it does not flow enough, it because the length is not optimum for the rpm where the VE is making peak hp. Think harmonic and play with the length.
ok what i would like to know in this post is where was the porting done?
The problem with the test subjects is that the standard is crap, the ported one could be worse or amplify the standard problems and the o2 one is known to be crap on the ve due to incorrect runner length
The problem with the standard manifold is not flow, but rather air speed. The reverse tapper causes the air to speed up entering runners then slow down through the runners, so the air is traveling slowest as it enters the port. So it really doesn't matter if the standard manifold flows double the head, it will still be a restriction due to air speed.
Reminds me of the old ford 4 bangers where the ports where too big and people would weld up the bottom of the port creating higher entry point and more importantly faster valve entry speed.