Headers vs. Ported exhaust manifold

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Dec 31, 2005 | 03:11 AM

#136

Silentbob343

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Joined: Oct 2005

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Quote:

Originally Posted by Mike@Forge

Equal length manifolds CAN also help time the pulses more evenly than a non-equal length manifold, HOWEVER, a properly designed non-equal length manifold CAN offer evenly time exhaust gas pulses as well.

You don't necessarily need an equal length manifold to achieve this.

One disadvantage to an equal length design, however, is that, often times, they require lengthening the runner to the extent that they have so much internal volume that spool time can often increase. This is a result of lower TIP (turbine inlet presure) because there is more space in the manifold to fill up before the exhaust gas reaches the turbo.

One good thing about the GT-Spec unit is that it is correctly pulse timed without having to use equal length runners, but it's tubular design offers improved flow without too much of an increase in internal volume.

Does this make equal length manifolds "bad" in comparison to non-equal length one or vice-versa? No. Just different.

That is interesting as I was under the impression that a twinscroll turbo needed equal length headers for correct pulse timing. I'm not an EVO owner, but I did know they had a twinscroll turbo and I just assumed they used a factory equal length header.

Quick EVO question; what is the firing order?

Dec 31, 2005 | 10:30 AM

#137

trinydex

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From: not here

equal length is not pulse timed. equal length will actually time the pulses such that two will arrive at the collector at once (one from each cylinder fired for a 4 cylinder engine). this pulse bunching in conjunction with the fact that the collector is an expansion in the flow line is suppose to prevent gases from traveling back up hte other pipes and back up it's on pipe as well. this of course is not fully efficient but making hte header long enough does prevent reversion as the pulses from the other two runners (in a 4 cyl engine) will be pushing their way towards the collector before any reversion makes its way back to the head.

so pulse timed is actual always unequal as you require at least 2 pulses fired at the same time to arrive at the collector at different times. twin scroll is actually just a different type of collector in that the cylinders that are fired together are paired up so there's no reversion. so the two are fired at the same time but they arrive at the half scroll at different times but one pulse doesn't go up the other runner because something is coming down that runner. this makes the header have hte capacity to be incredibly short and quick spooling. the twin scroll bascially alleviates any worthy from the "other" two cylinders which are fired at the end of the cycle, hence no loss in pulse strength and once again quicker spool.