I've been busy with some other list related mail lately, so I've missed the
start of this thread. But the GT6 is like some TR6 heads, and not like some
TR6 heads. Basically the GT6 shares the same casting as the TR5 and the
home market PI TR-6 motors, as far as I know. The carb equipped TR6 engines
from 69 to, uh, I should know this, 73?, had a different casting with different
intake port spacing. The water passages and exhaust ports are all the same.
And in truth, the difference in the intake port spacing is not so drastic
that I haven't seen examples of the wrong manifolds fitted, and the car thus
equipped still running.
The early 6s had a narrower intake port spacing, but the later ones had the
wider [we're talkng about 0.200" difference here] spacing. The GT6 heads were
milled down to give smaller combustion chamber volumes, so that matched with
the short stroke of the 2 liter motor the final compression ratio was still
usable. At this point, I should mention the article I started on TR6 engines
something like 6 or 8 years ago, but haven't touched since I got off on this
small chassis Triumph thing.
The bottom line is that if you are putting a GT6 head on a TR6 motor, it will
work. All TR6 motors get a compressin boost. Some TR6 motors need the later
[and better flowing] manifold. Putting a TR6 head on a GT6 will reduce your
compression ratio, and if it an early TR6 head, the intake manifold won't
mate properly. If you want to bulge you bonnet, you can use the TR6 manifold
and carbs.
mjb.
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