Hi Vance,
Yes, I would agree. I was trying to give a generalized list of
considerations for the theory of head work.
I raced GP, supersport and superbike motorcycles and quickly realized that
keeping the SPEED of the air-fuel mixture is one of the keys to good
performance (especially in terms of response). All parts must be mathced
(and I don't just eman in alignment). Overly large ports, valves, and even
carburettors that are too large can indeed slow down flow rates and/or
hamper the air flow.
What you had to say about the later TR6 head is interesting in terms of its
flow characteristics. I didn't know that. So are you saying that a better
performance option might be to get a later head and mill it to early
compression ratio standards? Thanks for the response.
Sincerely,
Dave Herbert
From: "Navarrette, Vance" <vance.navarrette@intel.com>
Reply-To: "Navarrette, Vance" <vance.navarrette@intel.com>
To: TR6 Triumph <tr6_1969@hotmail.com>, 6pack@autox.team.net
Subject: RE: LIST of things to do when doing your head
Date: Thu, 1 May 2003 08:10:58 -0700
Dave:
I would add a caveat here; It is not based on personal experience, but
is
based on what I have read in David Vizard's book "The theory and practice of
Cylinder Head Modification". This book specifically addresses the GT6 and
TR6 6-pot motor.
Vizard claims that the later ('wide port') 6s have an excellent port
design
that if anything, is already too large. He recommends not enlarging the
ports at all.
The only changes to the ports he recommends is to blend the short side
radius in the valve pocket, and slightly enlarging the valve pocket on the
long side to create a slight venturi.
Vizard claims that the power gains to be had on the 6 are to in
reducing
valve shrouding in the combustion chamber. He claims that enlarging the
ports on the later heads will reduce horsepower because the velocity of the
incoming air-fuel charge drops off unacceptably. The early heads do not flow
nearly as nicely, and benefit from cleaning up the ports. 'Course the early
heads had a higher compression ratio, and so made more power despite their
flow limitations.
On the later heads, milling to raise the compression is the
single biggest pop for power you can get. So in order, on a later head
Vizard says to:
1. Raise the compression
2. Reduce valve shrouding
3. Blend/reshape the valve pocket
If you want to soup up your 6, this a great book. It has
some really nice drawings on how to reshape the chamber and valve pocket.
I recommend it.
Ciao,
Vance
P.S. The book can be ordered at www.amazon.co.uk. Best I can tell the
book
is unobtainable in the US for a reasonable price.
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