Does anybody know off hand....

[Ian Szgatti]

what kind of compression readings should you get from a 3300 GM motor in great shape... the engine is from 1990. my manual only tells me what the minimum levels should be. thanks.

[maxwedge]

Lets start here, engine cranking rpms are a big factor in compression, be more concerned with the balance between the cylinders, no more than 10% variation. On an engine that old somewhere between 120-150 is good.

[Ian Szgatti]

Originally Posted by maxwedge

Lets start here, engine cranking rpms are a big factor in compression, be more concerned with the balance between the cylinders, no more than 10% variation. On an engine that old somewhere between 120-150 is good.

good point on the engine rpms. hey your the one who taught me to keep the throttle open whilw doing the test.

point to all this is, I got another car like mine and tested the engine... battery was ok, but didnt spin the engine to fast. My readings still came out from 125 to 150 across all cylinders. I was happy with that concidering the engine in my daily tested at 95 to 115.

Max, I find it interesting, these are both fuel injected 3300 motors, each with kilometers in the 290,000's. My low compression engine has been taken care of so well since i got it at 230,000... while the guy I got the other car off of hasnt even done a tune up in the two years he had the car... the oil in it is so black and dirty... how is his engine better than mine???

Either way, i do plan on swapping the two... is there anything of particular interest you might suggest?

[maxwedge]

Lots of variables in this compression business, carbon build up can make one engine look better, for one. A leak down test is much better, this tells you if there is an exh or intake valve issue and any excess ring blow by, these issues really don't show up in a compression test.

[Ian Szgatti]

Originally Posted by maxwedge

Lots of variables in this compression business, carbon build up can make one engine look better, for one. A leak down test is much better, this tells you if there is an exh or intake valve issue and any excess ring blow by, these issues really don't show up in a compression test.

thanks... you may have just answered my other question... the engine i bought, also a 3300, has equal miles to my engine in use, but compression is much higher... i suppose that seeing as my engine is SO clean, and the owner of my spare never serviced or flushed it or changed the oil for that matter... the increase in compression is probably due to the build up of CRAP... thanks Wedgie... and i'll definately do a leak down test.. i just want to buy my own kit when i can