potential buyers compression test

[SHYUMIDESUGA]

Some of you may know that I am selling my rolled gtr.
Since the body is no good, but most of the drive train & engine had no damage, basically that is what I'm selling.
I had some guys come by and do a compression test.
But they did a few things that I thought were weird.
Just note I had not started the car for a while and the battery is weak.
1. When doing the compression test, they did not have the throttle open.
2. They did not hook up the battery to a power source.
3. The test was done cold and not warm.
The numbers came out to be about 140 on four cylinders and about 130 on two (it was read out loud).
Since the compression should be at closer to 170 they want cheaper.
But I had never seen a compression test done in this way and I was under the impression that if done properly, compression should be above 150 not 170.
There were several other points that I thought strange about the buyer, but keeping that aside, this compression test is not normal.
I don't have a tester, but have seen it done many times.
I just need to check in with others about this since I don't have a good feeling about it.
If the buyer is browsing around and sees this thread, feel free to comment.

[DrMango]

no that sounds like(in my experience) that they, either had no clue what was going on or that they were trying to make a low test so you would sell cheap. Either way you have valid points and something is fishy there

Kyle

[mcfly]

those numbers are good and you are allowed up to 14 psi deviation between cylinders on a healthy engine.

171 may be the nissan "new" spec but I have yet to see even a rebuilt rb pull 170's. One of those mythical numbers. You have a healthy used engine though. Maybe they are used to higher static compression motors and are basing their numbers off past results.

[DrMango]

but typically arent you supposed to crank on a consistant battery at running temp? and i know ive heard people say make sure the pedal is to the floor..
McFly is right though. almost every RB that ive seen that was considered in good running order was around 140-150 area. ive never seen one in the 160s consistantly across the 6 cylinder

btw how many cranks did they do per cylinder?

Kyle

[SHYUMIDESUGA]

DrMango
We did about 5 to 6 rotations per tested cylinder.

Mcfly
He did mention Civic type R motors pushing upwards of 200 psi, which I thought was irrelevant.

There were a few other points they brought up regarding import and skylines that were doubtful, but I'll keep that out of here.

It's good to know that the engine is in good shape.

[m_melen]

did they do a wet test with oil in the cylinders? might be beneficial for you to know whether the problem is the rings or something else in case that gets brought up.
i've never heard about putting the pedal to the floor in a compression test. anybody else do that?
in general you want all your cylinders to be within 10% of each other at worst, or within 10% of the middle number. so if your average one is 140, the others should be between 126 and 156.

[DrMango]

haha anyone that brings honda motor tech into the RB world needs a wake up call. High compression N/A motors will always do a considerably different compression test than a really low compression turbo motor lol

Kyle

[DrMango]

not so much the pedal to the floor but to have the trottle body wide open for air to reach the cylinders with ease i would guess. just how i was told to do one when i did my first test

Kyle

[mcfly]

but typically arent you supposed to crank on a consistant battery at running temp? and i know ive heard people say make sure the pedal is to the floor..
McFly is right though. almost every RB that ive seen that was considered in good running order was around 140-150 area. ive never seen one in the 160s consistantly across the 6 cylinder

btw how many cranks did they do per cylinder?

Kyle

certainly, but the numbers were good so i wasnt going to bother about the way they did it. There are enough threads regarding that.

It's all dependent on the starter as the psi rating is for 300rpm.

[archaeic_bloke]

ive had my motor compression tested twice since ownership... it was done by 2 different mechanics, and both times the #'s came out the same... the motor was warm before each test and im not sure wether they held the throttle open or not,

but i observed both times, one time had a digital gauge and the other a mechanical. and ya both times they had to hook up the battery to another source as the battery wouldnt push past a few cranks!

anyways both times my motor saw compression #'s above 160... typically 165 plus or minus 4 PSI... mostly minus though lol....

on another note ive seen people run their motors for a few years after a compression test showsed 120! they just up the boost! lol

[DJ]

those numbers are good and you are allowed up to 14 psi deviation between cylinders on a healthy engine.

171 may be the nissan "new" spec but I have yet to see even a rebuilt rb pull 170's. One of those mythical numbers. You have a healthy used engine though. Maybe they are used to higher static compression motors and are basing their numbers off past results.

I don't know if my tester is reading bs number but I did a compression test on my gtr and pulled 170(-1 or 2 ) on the first four and #5 and #6 read 165.I re tested later on and same numbers showed up

[SHYUMIDESUGA]

Yeah I'm not sure why the honda motor was brought up.
From the speech, probably to emphasis that my numbers were low...

But the numbers were more or less consistent.
They would all be within 10% for sure.
The test was dry, but I guess a wet test could have been done if there was a concern with a particular cylinder.

If the pressure is too high wouldn't we have problems with detonation?

Hmm, so I guess the numbers are good as is.
Though I still think the proper way to do it is with a battery hooked up and throddle open.

[DrMango]

i would say that if someone is getting 170(DJ)compression on your test, then its likely you have a rebuild motor. just my guess. either way, good car to own

Kyle

[mcfly]

I don't know if my tester is reading bs number but I did a compression test on my gtr and pulled 170(-1 or 2 ) on the first four and #5 and #6 read 165.I re tested later on and same numbers showed up

i would bet on your starter being very happy with you

[DJ]

i would bet on your starter being very happy with you

Yea...I thought about that