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Compression results (archive)
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Posted by ian M635 UK on June 15, 2002 at 21:46:49:

OK chaps did the compression test for a second time with a more accurate guage and got the following results

Engine warm, throttle fully open, fuel pumps disabled.

Cranked engine over 7 times on each cylinder until max pressure reached.

No1 194 PSI
No2 197 PSI
N03 195 PSI
N04 200 PSI
N05 195 PSI
N06 197 PSI

Repeated test with a little oil down the bores and got about an extra 5 PSI on each cylinder.

Engine has 156k miles and was rebuilt (new rings no rebore) at 77k miles.

With a compression ratio of 10.5-1 I would have expected around 150-160 PSI. The results I have seen good?

My problem is that if these are OK then it does not explain why I have a power drop off above 4500rpm. Top end is a little noisy and the cam lobes seem worn (ridge can be felt on some of the lobes. I'm thinking that just a change to new cams would bring back the lost power. I have been offered Schrick cams in the UK for £1200 for a pair (272 degree vs origonal at 264 degree). These require no machining of the head but it is recommended that new valve springs are used due to the increase in valve lift.

New origonal cams cost £1000 per pair from BMW.

Which way do I go? will schrick cams need a remap? Can I get the old cams reprofiled and save £100's

Let me know what you think.

Regards

Ian

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