Does anyone happen to have info on what the cylinder compression range is for the 4.3 Vortec? If they are different from various years, I would like to know what the recomendations are for the early, mid and later 4.3 Vortec motors, just for infomational purposes. Right now I'd really like to know the minimum and maximum PSI compression for the 1998 model year.

 

The minimum compression in any one cylinder should not be less than 70% of the highest cylinder. No cylinder should read less than 100 psi (690 kPa).

For example, if the highest pressure in any one cylinder is 150 psi (1035 kPa), the lowest allowable pressure for any other cylinder would be 105 psi (725 kPa).

This is for your '98 Vortec 4.3L

 

Is there a maximum to the compression? I only ask as an engine I am inquiring about registers 190-200 on all cylinders. It has 103K on it and is in a 98 Blazer. I'm contemplating buying the engine for my 97 Bravada.

 

Well, I did some more reading up on the subject and it seems that normal is between 160 psi and 190 psi. I have never liked to see the compression any more than 10 psi apart, cylinder to cylinder, but what I stated first was from GMs definition of proper compression ratio... I wouldn't be worried about a 200psi reading. When it gets up around 220 psi on a 9.2:1 compression ratio... Higher than normal compression readings can be caused by the buildup of carbon on the top of the pistons.

For a comparison, when I rebuilt the motor in my Chevelle, I had 10.5:1 compression pistons and was running 255-265psi on all cylinders after the dyno throbbing was over.