I remember asking a question about my wacky compression ratio on my
1500 Spitfire, potted history follows :
Engine running rough leaking oil, compression test revealed three pots
up at 165 +- 5 and one pot reading 50 !! After putting a little oil
in the pot in question and seeing no change I changed the head for a
spare that I have had lying around. Retest the compression and still 50.
Blast drat and blast. Head comes off as does sump and the piston in question
gets taken out. The 2nd compression ring is in about 25 different bits.
I presume that no amount of oil in the cylinder would have helped that
lack of compression ! A new set of pistons 50 pounds and a new set of gaskets
and the car all went back together and started. Pinked like crazy and had
no real power. I tested the compression again (this time in all four
cylinders not just the problem one). The compressions were all up at about
190 psi !! (this before the rings had seated). I then put the original
head back on and three head gaskets 20 odd hours labour (mine thank god) and
not many $$$ and it works !!! The engine runs much better although it is a
rough but I have only set the timing statically and the carbs are probably
a bit out.
Any way the original question can you up a 77 American Spit to 9:1 by using
74 pistons. All I can say is that the pistons I took out and the ones I
replaced them with both came just level with the top of the block and were
not dished or domed in any way. So if yours are dished then if you replace them
with flat pistons you may well find that the compression goes up to 9:1.
Ben Hodson hodsonb@prl.philips.co.uk
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