Rb25det Compression

[slo33]

hey all, just did a compression test on my car and was curious about the readings,

1- 120

2- 119

3- 120

4- 120

5- 119

6- 119

i would just like to know all your opinions on the condition of my engine

thanks

slo33

[Abo Bob]

Nice and even.

[chrissso]

Hmmm, just got mine done and it as 150 accross all 6. Well, that's what I was told... Anyone else know what it should be?

[Tosh]

Sure it's nice and even but below minimum reccomended.

Safe compression is anything between 135 ~ 180psi (as per the Nissan Japan Service Manual)

Your engine is tired.... it's had a hard life and needs a refesh.

Re-coondition the block & head, new bearings and piston rings and you should be fine... budget for new pistons just in case but I suspect you may get away without them. However if you plan on putting horsepower into this engine then I suggest you put forged pistons in. Tomei make very nice 0.5mm (20 thou if you speak to any Australian engine builder) overbore pistons for the RB25. CP Pistons are an alternative if your busget isnt that high. Also don't forget to put a 1.2mm Head Gakset in if you're goin to run higher boost.

[blind_elk]

Before you pull the engine apart,

did you do the comp test with WOT?

[Duncan]

And did you have a battery with a heap of power?

And was the engine warm?

And did you let it crank to maximum pressure for each cylinder?

[Konrad]

  slo33 said:

hey all, just did a compression test on my car and was curious about the readings,

1- 120

2- 119

3- 120

4- 120

5- 119

6- 119

i would just like to know all your opinions on the condition of my engine

thanks

slo33

<{POST_SNAPBACK}>

I got my compression test done with around 130 across all cylinders. Motor seems fine, mechanics said that was a good result.

[wrxhoon]

Dont pull your engine out , it looks like you ahve a good engine there .

The comp test gauge may be reading low , who did it ? if a pro did then treir gauge is reading low and they probaly know it .

If your engine was stuffed its unlikely that it would be so even , my bet is it woul vary a lot more than that , regardless if you are loosing comp from valves or rings .

Do a leak-down test if you want to be sure .

Standard comp for rb25det is 12.2kg /cm2 (about 170-175psi ) @300rpm , limit 9.2 and difference limit between cil 1 kg/cm2 .

rb25de standard comp is 12.8 kg/cm2

rb26 dett 12kg/cm2

[Tosh]

I wouldn't say that an engine down on compression by over 30% is a good engine. Sure the gauge may be reading low and it wouldn't be a bad idea to get a test done somewhere else, however if this is the true compression of the engine then it needs a refresh.

[Tosh]

Also an engine doesn't have to be blown up to need a re-build. If it's had a hard life but has been serviced and looked after properly then the compression test should look like this one. If something happened like a cracked ringland or dropped valve, then 1 (or more) of the cylinders would read lower than the rest for sure.

[siksII]

  SW20-GT said:

I wouldn't say that an engine down on compression by over 30% is a good engine. Sure the gauge may be reading low and it wouldn't be a bad idea to get a test done somewhere else, however if this is the true compression of the engine then it needs a refresh.

<{POST_SNAPBACK}>

i doubt it would be worn like that, but anyway as an example i had a compression test done for a friends car one gauge read 160psi across first few cylinders before getting jammed, grabbed another working compression gauge it read 140psi across the cylinders.

[wrxhoon]

  SW20-GT said:

I wouldn't say that an engine down on compression by over 30% is a good engine. Sure the gauge may be reading low and it wouldn't be a bad idea to get a test done somewhere else, however if this is the true compression of the engine then it needs a refresh.

<{POST_SNAPBACK}>

I didnt say that either , what i said was "its unlikely that a worn stuffed engine would have even compression " not imposibble though just unlikely .

Old worn engines dont have so even compression on all cilinders and that leads me to believe that it may have good comp much higher than the test .

If the true comp is 120 psi on all cil that engine would be gutless in stock form with stock or near stock boost a 6 cil bommy will kill it .

Thats the reason i suggested he does a leak-down test that will prove the state of his engine .

[slo33]

it was a cheap gauge and the engine was cold as . . . . would there be a dif if it was warmed up

[slo33]

and my car seem to run better than most other 33's, i raced another 33 with front mount, 13psi and 3" exhaust and i beat him by car lengths ( my car just had standard shitty little side mount cooler, 11 psi and 3 " exhaust) it made 240 at the tyre spretty easy though

[race_snooze]

240 what hp i hope

[siksII]

  slo33 said:

it was a cheap gauge and the engine was cold as . . . . would there be a dif if it was warmed up

<{POST_SNAPBACK}>

there will be a BIG difference if the car is warm, try it and see.

[skyzaman]

Just got a compression test done today theres abit of difference in the results, but overall looks pretty healthy

Dry / Wet

1. 160 / 180

2. 160 / 170

3. 150 / 170

4. 155 / 175

5. 155 / 190

6. 160 / 180

Edited January 10, 2008 by skyzaman