Compression test completed on RB25DET

[PHaT MR30]

Oh i just did this over the weekend, turned out ok, but i am not sure what the factory specification is for it. Here are my results:

#1 - 140 psi

#2 - 150 psi

#3 - 140 psi

#4 - 130 psi

#5 - 140 psi

#6 - 140 psi

this is only rough figure i am guessing as it was only a cheap Hella Compression tester that i borrowed off a mate and he said he dunno how accuarate it is, main this is that there was no major drop across the board.

[Nozila]

out of curiosity how much are compression guages

[Duncan]

I picked one up at super dodgy auto on the weekend. About $50 but there were cheaper ones. The one I got had a screw in fitting to the spark plug hole, the cheaper ones have rubber thingies you just push in and try to hold tight.

Of course good ones are much more expensive, $100+

Sorry I don't know the target compression for an rb25

[SteveL]

#1 - 140 psi

#2 - 150 psi

#3 - 140 psi

#4 - 130 psi

#5 - 140 psi

#6 - 140 psi

Cheap gauges aren't accurate as Duncan said so these figures are a guide at best. The biggest worry is the difference between cylinders 2 and 4. Nissan recommends a maximum diff between cylinders of 14psi pretty much regardless of engine type, so these are well outside that. I'd recommend getting an accurate compression test done or, preferably, have a leak down test performed which is a far better indicator of engine condition.

Were these tests done with engine at operating temp, throttles open, etc ??

[R33vit]

Cheap gauges aren't accurate as Duncan said so these figures are a guide at best. The biggest worry is the difference between cylinders 2 and 4. Nissan recommends a maximum diff between cylinders of 14psi pretty much regardless of engine type, so these are well outside that. I'd recommend getting an accurate compression test done or, preferably, have a leak down test performed which is a far better indicator of engine condition.

Were these tests done with engine at operating temp, throttles open, etc ??

From memory you are allowed around 10% difference between cylinders, meaning between 1 & 2 , 2 & 3 , 3 & 4 , 4 & 5 and 5 & 6 not between 1 & 3 or 2 & 6 for example.

[SteveL]

From memory you are allowed around 10% difference between cylinders, meaning between 1 & 2 , 2 & 3 , 3 & 4 , 4 & 5 and 5 & 6 not between 1 & 3 or 2 & 6 for example.

14psi max variation between cylinders is pretty much a universal spec for Nissan engines, and it's between any 2 cylinders not just pairs.

[R33vit]

14psi max variation between cylinders is pretty much a universal spec for Nissan engines, and it's between any 2 cylinders not just pairs.

Like I said, It has been a long time since I worked as a mechanic

[discopotato03]

I hate your posts Sam , I keep loosing sight of the text .................

[PHaT MR30]

yeh i did it with WOT, but not at operating temp (for obvious reasons!) i assumed the differences could have been a factor of this cos of lack of oil in bores.

the unit i used was about ~$100 and screwed into the plug hole

[R31Nismoid]

mine were about 140 too... wel, 3 of em.

Two were 110... and lucky last was 70

needless to say i had 3 stuffed ringlands/pistons. With the 3rd being really farked.

So 130-150 sounds ok to me. Leak down testing would show more though.

[blur]

you would be surprised the amount of difference there is with incorrect operating temperatures and compression tests. try it again when its warm im sure you will find the engine is ok.

[siksII]

as blur said make sure the car is hot when u do it, and also make sure u have a good battery connected, (battery will affect cranking speed and compression readings)

outright readings are not important its more the variation, and if those readings were accurate your engine i stuffed, but its probably just the way u did the test. do it again properly and you should get some proper readings.

as a guide the last compression test i did on a rb25 gave figures between 170-173psi (less than 2% difference) although as i said before dont take the outright figures too seriously.