Mark wrote:
> What are the differences in the heads on various model years?
>
> Is there any way to tell what head is on the engine without disassembling
>it?
Mark:
It is easy to tell which head you have. (early or late, pre-'72 or
post-'72) The different heads also require two completely different intake
manifolds. The early (pre-'72) intake manifold is much shorter in
appearance than the post-'72. The easy way to tell is to locate the three
upper bolts or nuts that secure the manifold to the head. Each of these
bolts or nuts are centered above and between the #1 & 2 intake runners,
the #3 & 4 intake runners, and the #5 & 6 intake runners. If these are
long bolts that pass through drillings in the manifold casting for their
entire length (maybe 3 inches or so?) then you have the early head. If you
find a short stud with a nut that clamps against a flange on the head end
of the intake runners, then you have a late head. For a perfect
illustration of this difference look in TRF's blue Spare Parts Catalogue
(volume 1) at Plate AT, which is opposite page 49.
The two manifolds are NOT interchangeable, due to the different spacing
between the intake ports in the two heads. But, as far as I know, you
could put an early head on a late block and vice-versa. Someone please
correct me. However, because (if) you have an early head, this does not
necessarily mean it is 8.5:1 as it should be. Likewise, a later head isn't
necessarily 7.75:1, either. (Like mine... I had it milled to 9.5:1) Since
milling material off the cylinder head's surface increases compression
ratios, and since this also changes the THICKNESS of the cylinder head, you
should be able to calculate the compression ratio by measuring (accurately)
the thickness of the cylinder head. (from the valve cover gasket mating
surface to the cylinder head surface)
I had to do this once with a head from a parts car...the DPO had milled so
much off the head that he had to shim up the rocker pedestals. I needed to
know what compression ratio he had made it. In Kastner's Competition
Preparation Manual I found specs on thickness of cylinder heads, both stock
(I think) and a couple of different *racing* ratios. From these figures
somehow I mathematically figured out that this head was 11.8:1. (the ring
lands had shattered in the block!) So, if you can figure a way to measure
the thickness of that head, you should be able to determine if it's been
shaved, and by how much, giving what compression ratio.
Sorry, I can't find my Comp manual anywhere... if you don't have it
yourself, maybe someone else on the list can locate the info I'm talking
about. My memory on this is pretty spotty, since it was about 8 years ago.
Good luck!
Pete Chadwell
1973 TR6 CF10732
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