Stupid Question

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75dartsport

75dartsport

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Probably a stupid question, When doing a compression check will the compression reading give u a clue to what kind of compression that motor has, such as 9 to 1 or 10 to 1 or so on. Never really paid much attention before as long as they were close to the same on all cylinders. The reason i'm asking is when ordering a cam they ask for the cylinder pressure. What should a mid 70's stock 360 run as far as cylinder pressure?
 
Probably not much over a hundred on a well used stock engine. Mid 70's stock 360's were smog legislated dogs, as were alot of engines then. Stock compression was way down. How many miles? Whats your elevation?. I dont think there is a direct correlation between CR and cylinder pressure, but rather a trend. What did you find on the test?
 
Is it true you should pull all spark plugs to get a good reading.:dontknow:
 
memike said:
Is it true you should pull all spark plugs to get a good reading.:dontknow:
Click to expand...

Yeah , you should pull all the plugs and hold the throttle wide open taking the reading no sooner than the third stroke.

As far as cylinder pressure in a mid 70`s 360,.. wow,.. they`re probably around 8-1 CR when new ,so pressure after years of wear and tear is probably like 408duster said.....100lbs.??
 
There is really no correlation between cranking compression as read by your guage, and the actual static compression built in to your engine. In order to get the actual static C.R., you need to know things like the exact c.c. measurements of the combustion chambers in your heads, piston design, depth of the piston in the bore, head gasket size and thickness, etc. 408 and John are probably pretty close on your cylinder pressures.
 
Compression ratio is a mechanical ratio of the cylinder & combustion chamber and is set. Cylinder pressure is just that, pressure while the engine is spinning and is variable depending on camshaft opening and closing rates for example.

The two aren't exactly connected but, here is a chart that shows compression ratio vs cylinder pressure. I have checked this chart against "real" engines that I have built and it is about 95% accurate. Using this chart an 8:1 compression ratio motor should have somewhere between 125 to 150 psi cranking pressure.

http://www.moparts.com/Tech/Archive/clutch/1.html


Chuck
 
340mopar said:
Compression ratio is a mechanical ratio of the cylinder & combustion chamber and is set. Cylinder pressure is just that, pressure while the engine is spinning and is variable depending on camshaft opening and closing rates for example.

The two aren't exactly connected but, here is a chart that shows compression ratio vs cylinder pressure. I have checked this chart against "real" engines that I have built and it is about 95% accurate. Using this chart an 8:1 compression ratio motor should have somewhere between 125 to 150 psi cranking pressure.

http://www.moparts.com/Tech/Archive/clutch/1.html


Chuck
Click to expand...
where do i see this chart?
 
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