Junk yard motors

[dp213]

The yard I get motors from doesn't give milage but they do a compression test and tag the motors with those results.

 

My question is, what is the original compression in an early 2.2 motor supposed to be. 1990-1995 motors.

[1 Lucky Texan]

mutiply the cr and atmospheric pressure ?

 

if cr = 9.7 and atmo = ~ 14.7, that's a little over 140psi.

 

i've read you want cylinders within 7psi of each other too.

 

dunno how low you draw the acceptable threshold...

Edited November 22, 2016 by 1 Lucky Texan

[robm]

That method doesn't really work, because you are measuring gauge pressure (pressure above atmospheric), so if it works, it should be 14.7 x (CR-1).  But that is way too low, as it ignores temperature rise due to compression, and dynamic effects of the air moving into the cylinder.   Even with a CR of 8.5:1, you can see over 150 PSI on the gauge, which would never happen if that formula was accurate.

 

So, find the engine with the highest compression figures, and with the least spread between cylinders.  It is not an accurate measurement, just a good guess at finding a motor that has plenty of life left in it. 

[1 Lucky Texan]

^^^ yes, gauge readings are subject to 3-4 moderating factors. cam overlap and timing, altitude/local atmospheric pressure, temp, etc.

[dp213]

Cool, the motor I just picked up for my 3rd try in my Gt has 170 across the board