Compression Spitfire UK specs

[MichelvdM]

Hi guys,

The compression ratio of a Spitfire 1500 seems to be 9.0:1. I am not sure how to translate that to Bar.
I am measuring 8,7 8,4 8,5 8,8 Bar.
Does these values look OK?

Thanks,

Michel

[Nick Jones]

There is no direct relationship between compression ratio and measured compression pressures as valve timing (camshaft characteristics) and cranking speed also affect it.

For cylinder compressions I find psi easier - all cylinders are between 122 and 127psi.  It is good that they are all pretty close.

I would expect higher pressures, but it depends on what camshaft you have fitted, how your gauge reads and also how the test was done.

My technique is to warm the engine to operating temperature, the remove all spark plugs and disable the ignition system (and fuel if injection).

I then test each cylinder in turn, allowing 5 compression strokes and watching the way the pressure builds.  A healthy engine should build the majority of the final compression pressure in the first two strokes.

Finally if I get lower than expected figures or some are very different (say more than 10 psi) I repeat the test putting a table spoon of engine oil into the cylinder first.  This is the "wet" test and the intention is that the oil provides additional sealing to the rings.  If you get big pressure increases on the wet test this implies that there is ring leakage.

If I'm telling things you already know - my apologies.

Cheers

Nick

[Rich_s]

Did mine recently and found 145 - 150 on cold engine, yours seem a little low but all close together so maybe nothing to worry about.

rich

[CHRIS211083]

Dont forget the throttle should be wide open when cranking.

CHris.