Don
Universally referenced web guide on DIY head porting
http://www.sa-motorsports.com/diyport.shtm reads as follows:
"In most cases, you never port match the exhausts. Many stock exhaust
manifolds and virtually all tube headers will have larger port sizes than do
the heads. You want that "step" from the port to the larger header tube or
exhaust manifold because, as pressure pulses flow back and forth in the
exhaust system, it acts as a "reversion dam" by resisting back flow of
exhaust gases into the port. If you end up with the rare situation where the
stock exhaust manifold has ports smaller than those in the head, you will
need to port match. Use the same technique used to match the intakes. "
I'm just getting prepared to port my head and find this discussion of
interest.
Jerry Shaw
Date: Sat, 13 Nov 2004 09:00:07 -0500
From: Don Malling <dmallin@attglobal.net>
Subject: Port matching and Falcon Group 44 headers
The round tubes on the Falcon Group 44 SS headers are welded to a head
mounting flange. The head mounting flange has rectangular ports which
appear to match the exhaust ports in the head. My plan is to port match
these rectangular flange ports with the head ports.
The question...
I've noticed that the edges of the round pipes infringe on the corners
of the rectangular flange ports. That is to say, the diameter of the
pipes is slightly smaller than the diagonal measure of the rectangular
flange ports. Based on the size/thickness of the weld that attaches the
pipes to the flange, and which is on the external side of the pipes, it
would appear that I could safely file away this small portion of the
round pipe that infringes on the corners of the rectangular flange
ports. This is a small infringement, but none-the-less, in the very
corners, the weld material is visible, so I would have filed through the
thickness of the pipe and would be filing into the weld at that point.
Should I do this or am I worried about nothing? That is, will doing this
provide any noticeable flow improvement for a street engine? It would
seem to me that even small obstructions would/could lead to a
significant amount of turbulence, and that it should be done.
Thanks,
Don Malling
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