>Before pulling the head we did a compression check, 170-175 psi on all
>four cylinders, somewhat more than I expected, figured either a lot of
>carbon inside or high compression pistons.
Hi Barney,
It would seem to be common sense that high numbers from a compression
check means a high compression engine. Not necessarily. In really
high performance, high compression engines, the effect of valve overlap
and long duration associated with performance cams causes compression
to appear low when testing at cranking speed. Conversely, stock motors
with stock, mild camming could indicate a good amount of compression
since the valves are likely to be fully closed at the begining and end
of the compression stroke.
For example, my Tiger with 10.5:1 compression and fairly radical cam
gives compression numbers of about 150. It detonates violently on
anything but the highest grade of gas. My Jeep with its' ultra low
compression 360 V8 gives compression test numbers of 165-170 and never
pings using the cheapest gas.
The only thing meaningful in a compression test is consistency between
each cylinder, which, in the case of your '50 TD, is about perfect.
Hope this helps,
Don Daves <dondaves@ix.netcom.com>
Santa Cruz, CA
65 Sunbeam Tiger (his)
64 1/2 Mustang conv. (hers)
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