Compression question

Does anybody know what the stock compression for an 85 ca18et is?
thanx.

also to do a compression test you have to take out all the spark plugs and crank the engine, right. so will this still work eventhough it has 2 spark plugs per cylinder? or do you have to use a different method? :dontknow:

you will have to leave one of the spark plugs in each cylinder and have the compression tester in the other hole otherwise it won't make any compression. The most important thing is that not only is the compression within spec for each cylinder but also that the pressure is pretty even accross all cylinders, one low cylinder indicates a problem. If one cylinder is low a little oil into the cylinder (a teaspoonfull into the sparkplug hole) and a retest on a low cylinder can indicate rings (if the compression raises when you put oil in the cylinder), there are a few things you can do to narrow down problems while you are at it, most are probably mentioned in the manual.

thanks man. i don't have a manual yet, so do you know how much its supposed to be? :mrgreen:

I'm not sure where mine is, my mate might still have it or it's at home somewhere.

i did the compression test yesterday. all the cylinders were between
145-150. :D
so i guess i got a pretty good car for 250 bucks.
:firebird:

man some low compression well then again it is ca18 but im prety sure ur rings are gonn go soon i have a fully rebuilt ca20 and im getting 185-190 so just a thougth but u might wanna take the head off real quick and get a new head gasket and check ur side walls pull ur finger nail over teh top of teh cylinder if it is rougs ur rigs are about to go.

i did the compression test yesterday. all the cylinders were between
145-150. :D
so i guess i got a pretty good car for 250 bucks.
:firebird:

what motor you got

man some low compression well then again it is ca18 but im prety sure ur rings are gonn go soon i have a fully rebuilt ca20 and im getting 185-190 so just a thougth but u might wanna take the head off real quick and get a new head gasket and check ur side walls pull ur finger nail over teh top of teh cylinder if it is rougs ur rigs are about to go.

ca18 have .5less c/r so the number will be alot lower then the ca20e

OK, remember too that cranking compression usually doesn't have much to do with actual compression ratio. And yes, the CA18's are gonna have lower cranking compression than a CA20. But you can take an 11:1 motor with a huge overlap cam with a big LSA and read 160 lbs. Or if you advance the cam timing, sometimes you can get 200 lbs out of a 9.5:1 motor. Cranking compression has A LOT to do with valve timing events.

That's why you mainly just check for consistency from cylinder to cylinder. If you're within 10%, you're ususally good to go.

Perfect compression will be in the 180's, but no one is really going to be up there unless they just rebuilt the engine. 170 for a very healthy engine, 150 for a well used engine, and 120 for an engine ending it's life.

the factory compression on a ca18et is 171 psi

1st remove fuse to fuel pump!!!

to test properly you must remove all 4 plugs (US spec remove only 4) screw in comp tester in cyl NO1.
before you crank the engine over make sure the throttle is wide open (push accelerator to floor)
crank engine for about 10 seconds
make note of test then repeat on cyl NO2 and so on

edit: engine has to be warm

Perfect compression will be in the 180's, but no one is really going to be up there unless they just rebuilt the engine. 170 for a very healthy engine, 150 for a well used engine, and 120 for an engine ending it's life.If your engine is down to 120 PSI just give it more boost :twisted:...*lol*