300CE 24 Valve - compression spec
 

Does anyone know the compression specification (in PSI) for the 300CE 24 Valve - ie the 3 Litre M104 engine. My manual gives only the ratio - 10:1. Is there a way to figure the PSI out from the ratio?

Thanks in advance

David

Re: 300CE 24 Valve - compression spec
 

Cranking compression pressure is a function of compression ratio, valve timing, cranking speed, and the accuracy of the gage you are using. Specified compression pressures are usually determined experimentally and posted in shop manual specs, but you really don't need them.

The important issue is variance between cylinders. To perform a compression test, remove the plugs, disconnect 12V power from the ignition module (or ground the coil high tension terminal), and block the throttle wide open. The engine should be near operating temperature, not cold.

Crank the engine until the gage reading peaks - usually about six engine revolutions. Do the work as quickly as possible while the engine is still hot.

Most OE specs say variance of more of no more than 20 psi is acceptable, but a good engine will show less.

Duke

Thanks Duke

My mechanic say the compression is 'excellent' even though the dry range is 40psi (150 to 190). He say this variation is normal in his workshop with a dry test.