Bob Hutton wrote:
>
> Hi, My name is Bob Hutton and I've just joined the list. I own only a mere
>2500TC sedan but aspire to one day get hold of a Stag. Anyhow back to
>compression testing.
>
> Todd Sigety wrote
>
> >My test results were as follows, 155, 150, 152, 155, 160 and 115 (ouch).
> >I need to double check that last one.
>
> >If the pressure is too high, this indicates carbon build up in the
> >cylinder. I do not know what is considered too high (maybe mine?).
> >A large variation between two adjacent cylinders could be a bad head
> >gasket, if the readings are low, it could be valves or piston rings.
>
> I've recently done my engine up completely using 10 thou oversized pistons
>and there is definitely no carbon build-up. I get a compression reading of 180
>to 188. Should I be worried? Is that too high? What compression ratio does
>that make it? BTW, where I live near Melbourne Australia, we're about 400 ft
>above sea level. The engine is running beautifully, but I have to time it at
>about 2 degrees BTDC to stop knocking.
>
> Appreciate any comments.
>
> Regards,
> Bob Hutton
Bob,
Don't get me started on Too much compression. I think I wore that
thread rather thin discussing my 260 psi Spitfire. However, If the
compression is greater than it should be, that could in fact cause
the car to "ping" because it isn't getting enough octane to run the
engine quietly. Advancing the timing does solve that. As in my
recent experience, an over milled head will increase the compression.
I am not sure what the compression should be in your particular engine,
but 180 psi does not sound incredibly high. If you are running regular
gasoline, you might try upgrading to premium or trying an octane
booster to see it the "pinging" subsides.
Joe Curry '63 Spit
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