i had my compression checked a few weeks ago by two different people...one told me my engine was running right and had around a 11.5:1 ratio and that my engine had good compression...the other said that i had around 85-90 psi (or something like that) and said that it was time for a rebuild since other lt1 cars are around the 150psi area...one also said that you check compression by having all spark plugs off and the other said that you leave them in there an check them one by one...really need advice as i'm not too familiar with this ...please help...thanks

 

How did they check the compression RATIO? You can't check the compression ratio using a gauge. Compression ratio is actually a VOLUMETRIC RATIO. Compression ratio is defined as the volume of the cylinder at BDC divided by the volume of the cylinder at TDC. Now to check CYLINDER COMPRESSION you remove the all the spark plugs from the engine. You then place a compression gauge in a specific cylinder. The engine is then turned over and when the piston reaches TDC read the compression reading. You would repeat this for every cylinder.

 

thanks for the reply...it makes sense now...just wondering what they meant by 85psi as compression? is this good? thanks.

 

They measured CYLINDER compression, not compression RATIO. Was that the average compression of all 8 cylinders or just 1 particular one?

 

yeah, it was cylinder compression, sorry...the 85 psi was the average of all cylinders, is this good?...thanks a lot