Dave Fain wrote:
I am starting to clean up the ports on the head from my GT6 project car. I
already knew that the
engine was a mixed bag of parts because it has an early Plus block
(KD53420E), one piston with a
part number that doesn't match the other 5 and 3 rods marked #4. It is
getting new pistons and
will get balanced before it's assembled. The head also seems to have come
from somewhere or
other. My parts book shows that a Plus engine should have part number
517609 or 517610 head.
Mine is clearly marked 517528. Can somebody tell me what it is?
Later GT6's were supposed to have heads with larger combustion chambers and
used domed pistons. My engine has flat top pistons and the combustion
chambers don't seem to be much larger than on a MkI head. Could this
possibly be from a TR6 or TR250?
Dave. According to my records, your head is entirely appropriate to your
model of car. It was also fitted to Mk 2 2000 saloon up to commission number
ME50000, Mk 2 Vitesse and GT6 Mk 2 - and yours is the US Mk 2 called a GT6+
Just to clarify the numbers, the Stanpart number for this head as listed in
the parts book probably was 517610
and the stamped number of 517528 (this is the one you've found under the
valve cover???) is entirely correct. Be aware however that 517528 is not,
the part number but a production identifier - and only that. Check the
raised casting number. It should be 308351. In other respects, the engine
for your car did have flat top pistons, the exhaust valve dia was 32.0mm and
the pushrod length was 8 inches exactly.
Also, what thickness should I mill the head to to end up with around 10:1
compression? I will
be running headers and a Kent road cam and the car lives above 5000' so I
can get away with a
little extra compression.
Check the nominal height of the head to ensure it hasn't already been milled
by a PO. If still at factory spec it should be 3.300 inches. Sorry, but
can't advise how much you should mill for a higher comp but this particular
head wasn't brilliant anyway for increased performance. There's a lot of
turbulence in the porting and removing metal in the hope it will 'improve'
flow will probably do exactly the opposite. The later 219015 and 016 heads
with 30.3mm exhaust valves were a great improvement and were certainly found
on Mk 3 GT6 - but I'm not sure if these were fitted to US cars. The porting
was dramatically reworked and this resulted in some significant
improvements. If you can, I'd recommend just some careful polishing down the
inlet and exhaust tracts
but leave the metal very much in place. As for headers, you'll get the very
best extraction and scavenging using the former SAH/Triumphtune set up. This
is a three pipe set-up - eventually merging into one common pipe but starts
off linking 1 & 6, 2 & 5 and 3 & 4. It's certainly available in the UK -
about the US but cheap it isn't. IMHO, it really is the best you can get
though absolutely NFI on my part.
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