[6pack] Cylinder haed swap

[Vance Navarrette]

	John:

	There is more to this than the CR. The later TR6 heads, for
example, have markedly superior ports to the earlier TR6/TR250 design.
In addition, the later heads have a smaller exhaust valve that actually
flows better than the earlier larger valve because the valve is not
shrouded by the combustion chamber wall. The PI cars got the better port
design all along, but North America for some reason got badly strangled
smog heads instead. Only later as the CR continued to fall did Triumph
give us the good port design in order to make up for the niggardly 7.5:1
compression ratio.

	Lastly, the later TR6 manifold flows much better than the
earlier "square" manifold. Once again this was done so that the
miserable performance of a desmogged ("castrated" is a more descriptive
term) engine could be offset.

	If you want performance, you are much better off using the late
TR6 head and manifold, and milling the head to raise the compression to
9.5:1 or 10:1. This will require approximately 0.125" to be removed from
the head. 

	The earlier head designs give up too much in terms of flow to be
considered, IMHO.

	Vance

-----Original Message-----
From: 6pack-bounces at autox.team.net [mailto:6pack-bounces at autox.team.net]
On Behalf Of John Johnson
Sent: Sunday, October 31, 2010 5:35 PM
To: 6pack at autox.team.net
Subject: [6pack] Cylinder haed swap


Hi all,
         I am dropping a 1972 TR6 engine in my GT6 and had a quick
question
regarding combustion chamber size and compression ratio. Because of
extreme
hood clearance issues on the GT6 I want to use the shorter 1972 GT6 head
that
I have on the engine to give me additional hood clearance. I know the
combustion chamber is smaller on the GT6 head but the ports are the
same. Has
anyone made this switch on their TR6 or seen a chart that would give me
an
idea on compression ratio before I cc the heads? Thanks!

                                               John Johnson
                                              Columbus, Ohio