-------- Original Message --------
Subject: Re: Port Matching
Date: Sun, 08 Jun 2003 09:30:45 -0400
From: Don Malling <dmallin@attglobal.net>
To: john donnelly <pdonnel1@san.rr.com>, "Triumphs List (E-mail)"
<triumphs@autox.team.net>
References: <000101c32d78$acd93f70$0200a8c0@toshibauser>
FWIW, from David Vizard's "Tuning the A-Series Engine" 3rd edition 1999
page 248:
"The simplest way to achieve good forward flow but bad reverse flow, is
the mis-matched exhaust pipe. For years, the matched exhaust pipe has
been presented as THE route to maximize flow capacity. Forget it; such
thinking is out of date. Flow bench tests show that a stepped port/pipe
combination equals or betters the flow capacities of a matched one, as
long as the step is the right way and the mismatch between the exhaust
pipe and exhaust port is optimized. The "A" series engine is not as
fussy in this area as some cylinder heads, and fitting the square
exhaust port to round exhaust pipe allows flow in the forward direction
to be as unimpeded as it would be if the sections were matched. On the
other hand, when the exhaust tries to reverse flow, it meets the step
between the pipe and the exhaust port. Result: less reverse flow than
would otherwise be the case."
Don Malling
john donnelly wrote:
> I was looking through David Vizard's Tuning Standard Triumphs and found a
> section that discussed matching the port openings between the head
and the
> intake/exhaust manifolds. So I checked mine and found two of the exhaust
> ports were offset by about 3/16 inch. Since the exhaust manifold openings
> are bigger than head openings I didn't think it'd be worth the extra
effort
> since no restrictions exist.
>
> Has anybody did port matching? Was it a noticeable improvement?
>
> Thanks!
> John in San Diego
> '67 TR4A IRS
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