Compression

[dixiebabes]

Anyone know what compression (PSI) i should be getting in my 350i???

Regards Dix

[Wedg1e]

Upwards of 150 would be nice.

[adam quantrill]

Yeah ideally 160-165 but it does depend on your compression ratio.

[dixiebabes]

I only seem to be getting 140psi after 12 spins of the starter. Should i worry lads?

Regards Dix

[adam quantrill]

It's a bit low. Is this with open throttle?

Also, if you put a few drops of oil down the plug hole, does it come up?

Hot or cold engine?

[ed_crouch]

My 390 gives about 180 - 190PSI WOT or not, cold or hot. 10.5:1 CR.

Depends very much on the compression ratio of the engine. How many miles has it done?

[convert]

Are all the compressions pretty even over each bank?

[Wedg1e]

adam quantrill said:

Hot or cold engine?

Good point. If the lifters have pumped down you won't be getting full valve lift.

[dixiebabes]

Yeah 140 in all 8 pots when the engine is cold, and its done 69000 miles, the power seems to be there like? maybe a slight missfire if you blip the throttle on idle. Seems like there is a sharp intake of air at the filter then revs no problem.

Regards Dix

Edited by dixiebabes on Thursday 16th July 14:55

[adam quantrill]

Barely run in. 140 on a cold engine is OK, try it hot.

[GreenV8S]

Consistency between cylinders is the main thing to look for. The actual pressures will depend on various factors such as cam timing, and it's not simply a case of higher is better or lower indicates a problem.

[dixiebabes]

Mind at rest now. Thanks again lads your all worth your weight in gold

Regards Dix

[convert]

F**k me Jeff, in my case that's a LOT of gold

[Wedg1e]

dixiebabes said:

Yeah 140 in all 8 pots when the engine is cold, and its done 69000 miles, the power seems to be there like? maybe a slight missfire if you blip the throttle on idle. Seems like there is a sharp intake of air at the filter then revs no problem.

Regards Dix

Edited by dixiebabes on Thursday 16th July 14:55

You mean that gasp when you give it a bootful, before the engine spins up? Most V8s I've seen do that, they don't like to be blipped, there's too much flywheel mass

[dixiebabes]

convert said:

F**k me Jeff, in my case that's a LOT of gold

He he he N1

Aye thats the one wedg1e exactly as you say a wheeze like its got asthma.

Regards Dix

[dixiebabes]

convert said:

F**k me Jeff, in my case that's a LOT of gold

Steve i only thought it i never typed it ok LOL.