Compression Test

[BluThnder99]

Ok I have never done a compression test before so my question is how do i determine if the compression is accurate or not. I know how to do the actual test but what is the equation that needs to be done to find correct compresson ratio?

 

[inferno9898]

compression ratio is different from what a compression test will determine. compression ratio is just the ratio of the volume of the cylinder/combustion chamber at BDC versus TDC. a compression test will show you if any cylinder is losing air/fuel through the rings, gaskets, valves, etc.

 

[BluThnder99]

So how do you find out what your compression ratio is?

 

[bdcardinal]

look in your owners manual it will tell you what it is. i think its 9.5:1 from the factory, but i might be mistaken.

 

[inferno9898]

So how do you find out what your compression ratio is?

"How to build Max-Performance 4.6L Ford Engines" by Sean Hyland says 99-up PI engines have a static compression ratio of 9.7 to 1

 

[BluThnder99]

Its not for my mustang its for my Mopar its a 440, so I guess if I do the compression test and all cylinders are reading correctly I thinks it has to be more than 80% of 200 p.s.i. then my total compression should be what the manual says.