HAHA Compression test

voidfinger · Sep 16, 2007

Well guys, i did a compression test while the car was hot today. I was told they were suppose to be at 160. Here are the numbers

4) 162 8. 175
3) 150-160 7) 170-175
2) 160 6) 168-170
1) 160-170 5) 170

Ok, i had all the spark plugs out, the throttle wide open, and the coils unplugged.

The last oil change i put some 10W40 Havoline in there.

I turned the car over 4 times for the things.... i retried some again... that would be the second numbers beside the first... don't understand the higher numbers.

Also, i got some higher numbers when i cranked it more than 4 times...

So what you guys think? Does this sound pretty good? why would the drivers side be 10 more? just curious?

So you guys think it would be ok to throw some pi heads on it now??? i got a guy to do the compression and he said it was like 120 and 130's ... i was under the impression that my motor was about done for. What you guys think lol. :banana: wo hooo i'm jacked up.

ripper · Sep 17, 2007

Looks like a new motor. How many miles on it?

Mr Jones 4.6 · Sep 17, 2007

If you were turning it over 4 times and thats the numbers you got then its not looking to good. I would start thinking about saving for a Built PI engine. Its not horrible, but the engine is not going to run at its best, thats all. I would though start collecting funds to resolve the issue.

voidfinger · Sep 17, 2007

Stevo said:
Looks like a new motor. How many miles on it?

160K Yea it was good i think.

voidfinger · Sep 17, 2007

Mr Jones 4.6 said:
If you were turning it over 4 times and thats the numbers you got then its not looking to good. I would start thinking about saving for a Built PI engine. Its not horrible, but the engine is not going to run at its best, thats all. I would though start collecting funds to resolve the issue.

How is 4 times not good? thats what the haness manual told me to do... It had to go threw the whole stroke so 4 times should cover the whole strokes...Turn the key and bump it over 4 times..... :dunno: one said it looked like a new motor and another said it was worn out??? i was told that 160 was were it was suppose to be???

95-stang · Sep 17, 2007

I usually crank the engine until the gauge wont go any higher, a V8 is a lot of cylinders, you need to be sure you gave it a good turning over.
What you are looking for are major differences, [if you were racing thats different again] say a new engine would give 180psi, a worn motor might be 150 all round. But if you have 7 cylinders that read 160, and 1 reads 110 [only examples btw] then you know there's a problem.
Your figures dont look too horrendous, ok, theres a bit of difference , it could be the head gasket is not that good on the passenger side.
Is this motor running bad, just wondered as to why you are having it tested?

voidfinger · Sep 17, 2007

looking to put a set of pi heads i have sitting in the house on while i build up a cobra motor to put in...plus i'm putting in a t45 in there too. I was also wondering since it seems to have slowed a little, but i didn't know if it was the tranny slipping or the compression. I guess its the tranny since the compression is good. I was told that the new motors were suppose to be 160 ? is that not right? i see you said 180 ! Also, the motor was hot !!! and the coolant goes in on the drivers side... could that have caused the higher numbers on the drivers side? But it could have been that i didn't turn them over enough....

95-stang · Sep 17, 2007

180 was just an example, if a new motor is 160, with a few miles on it that will come down a bit with wear and tear.

voidfinger · Sep 17, 2007

so you think my motor is looking pretty good then? thanks dude.

reivaxtorres · Sep 17, 2007

i think you should be good to put the PI heads on. i just put mine on (well, kinda...still working on it) and my car has 158k miles. the cylinder walls looked good, felt really smooth, and im not too worried about the added compression. the headgaskets looked perfect as well. cant wait to get it up and running. :banana:

voidfinger · Sep 17, 2007

did you happen to do a compression test?

MeanGrn Gt · Sep 17, 2007

compression tests are meant to show you if you have any compression leaks (valves, rings, head gasket etc)

What you are looking for is for variance in #'s between each cylinder. There is no exact # you should have because it varies between each engine and how tight tolerances etc are. Generally if you are within 10% everything is in good shape. If one side is higher than the other that is probably head gasket difference. If ya have one cylinder that is low it is either the valve leaking or a ring. Squirt some oil in the cylinder and if it fixes it than it is a ring if not then it is a valve

You are supposed to keep cranking until the it stops building pressure. The motor looks like it is in good shape for having 160k. Mine which was supposed to have been rebuilt shortly before i got it was within 2 psi so i was happy.

voidfinger · Sep 17, 2007

yea i hear ya. I'm thinking it should be strait for me to put the heads on it. Plus i'm just doing it till i get my 4v ready

reivaxtorres · Sep 17, 2007

voidfinger said:
yea i hear ya. I'm thinking it should be strait for me to put the heads on it. Plus i'm just doing it till i get my 4v ready

hahahaha, thats what im doing!!!! but to tell you the truth, after working on mine, i dont think id want to work on a 4v, lol

and no, i didnt do a compression test on mine. never really bothered to do so, figured it would be a waste of time. car seemed like it was running perfect, which is exactly what the CR test would have told me

voidfinger · Sep 17, 2007

yep lol, i guess i'll do all the work on the 4v while its outside the car lol... to big to do it in ther car lol

reivaxtorres · Sep 17, 2007

voidfinger said:
yep lol, i guess i'll do all the work on the 4v while its outside the car lol... to big to do it in ther car lol

lets put it this way....to change the cams on a 2v, you can do it with the engine in the car. degreeing them might be easier with them off the car, but not manditory. with a 4v, they have to come off, no questions about it.

voidfinger · Sep 18, 2007

yep, thats why i want it right before it goes in ya know.

Jrgunn5150 · Sep 18, 2007

Your number's look great, the one side may have the cam out of phase slightly, or a slightly bad gasket as stated above, it's wierd, but not cause for worry.

BTW I would use some thinner oil than that 10w40, Mod motor's damn near run on oil, it need's to get up top ASAP on start up.

voidfinger · Sep 18, 2007

Yea i put the thicker oil in it b/c its got so many miles... i usually ran the 10w30 in there but i switched over b/c my dad said it would help the car last longer... since it probably has higher gaps in the bearings b/c of wear now... I'm not even going to do the head swap now... i'm thinking of throwing the npi intake back on and putting the stock mid and cat back back on it now. Clean the mid and make the mac cat back into a prodump. Do some high temp ceramic paint on them and leave them on the side till i put the 4v in there.. and sell the pi heads/intake/ and cams... o and the head change kit too.

reivaxtorres · Sep 18, 2007

the mod motors have small oil passages, so the thicker oil you use, the harder it is for the oil to get around. and since you already have all the PI stuff, i would just say do the swap, it will be worth it and it will hold you over till you get the 4v swap