Steve wrote:
I'm studying a TR-5? six cylinder head next to a late TR6/GT6 head with the
immediate difference being the spacing between the intake ports.
Steve, would you let me know the *stamped* head numbers for these two units?
You'll find
them on the front right side, just inside the valve cover seating. From your
description,
the TR5 unit is probably 516798 (fuel injected head) or 516323 (TR250) while
the unit for
the GT6 could be 219015. I'm in possession of a head applications chart that
hopefully
might highlight some key differences of which you presently remain unaware and
you ought
to know. That said, this tends to concentrate on the heads for the big saloons
that
stopped being sold in the States in 1967 but there are several references to
the GT6 and
US TR's.
Is there an advantage to be exploited with the narrow port heads over the
later wide ports?
As your query might also affect gas flow characteristics, it has been proven
with
convincing evidence that the later 219015 head with a 30.3mm dia exhaust valve
has
improved gas flow over the earlier and larger 32.0mm exhaust dia. It would
appear the
narrower exhaust valve unit has less turbulence around the base of the valve
guide than on
its earlier and larger relative. For normal road use, I don't think the
difference in flow
characteristics would bother a blind man on a galloping horse - but they might
be more
critical in racing applications. I've driven effectively identical cars in
which only the
heads had these differences and I couldn't detect any noticeable variance in
performance.
On a flow bench, the data suggests otherwise.
I guess my major question is why did the factory go to the wide port head at
all when the narrow port looks superior?
Mmm, with 15 different cylinder head references used in the 2.0 litre and 2.5
litre six
cylinder units between the early 1960's and the termination of production for
worldwide
applications, we're looking at a little more than just narrow and wide port
heads. Let me
know if you can handle an Excel spreadsheet and I'll let you have the detail as
an
attachment.
Cheers
Jonmac
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