Compression test results. Bad or still ok?

[erazor.]

Hi,

just bought a R33 GTST with 150000 km / 93000 miles. Engine fells strong, pulls nice and smooth. Nothing to complain

But today I did a compression test. Engine was warm, throttle full open, oil is at max.

Results: All six cylinders 8 Bar / 116 psi.

Is it still ok for a 24 year old RB25? Or should I expect it to fail anytime soon?

 

Regards 

[GTSBoy]

It's low. Not critically low, but very low compared to where it should be.

But, as I always say to people.....do you trust the compression tester?

[Duncan]

Generally, because test conditions and procedures vary, you'd be looking for consistency in the result (which you do have) more than the specific numbers. 

Apart from actual engine problems, bigger cams can lead to lower results, but so can incorrectly calibrated gauge, poor battery charge, test technique etc etc

It is higher klm so you should expect some ring wear by now, I'd keep an eye out for white smoke and oil consumption between oil changes, that should give you a good indication if they are worn.  In any case, those results are no sign you are about to have a sudden failure. Maybe just start saving for a rebuild (cost will vary based on how much you do at the same time)

[Butters]

I've seen some big variances in gauges, specially with so many "quality" ones getting around. I've had the same motor on the same day read 125avg on one gauge and 165avg on another.   Knowing your gauge and then looking for consistency is the key. It's not common that all cylinders read low.

[hypergear]

There are differences between compression testers. I've used two testers on my built engine and they varied 50psi in reading. As long as the compression between cylinders are even then the engine is likely to be good. 

[SiR_RB]

Maybe has a thicker metal head gasket ?

adjustabke cam gears or camshafts ?

 

results are consistent if you wish use another gauge and try again 

[erazor.]

 

13 hours ago, SiR_RB said:

Maybe has a thicker metal head gasket ?

adjustabke cam gears or camshafts ?

 

results are consistent if you wish use another gauge and try again 

Engine looks stocks except for R32 GTR wastegate spring(boost ~ 0,5 - 0,7bar)

I will try to do compression test with another gauge. Will report back when I get it done.

[GTSBoy]

24 minutes ago, erazor. said:

Engine looks stocks except for R32 GTR wastegate spring(boost ~ 0,5 - 0,7bar)

That's not a thing. Stock WG spring on RB25 is 5 psi, lifted to 7 by the bleed solenoid.

[Ben C34]

But why bother? Just drive it. Don't worry

[admS15]

Increase boost and drop epic skids, then post vids here

 

[Dose Pipe Sutututu]

Good tune, good parts, big boost, rip skids.

I had a 300 000km (maybe 400 000km, Edward Lees SE Odo windback) motor making 372kW and abused so bad on the track, skid pans, Mexico before it exploded 1.5 years later.

[niZmO_Man]

On 03/11/2019 at 9:55 AM, erazor. said:

 

Engine looks stocks except for R32 GTR wastegate spring(boost ~ 0,5 - 0,7bar)

I will try to do compression test with another gauge. Will report back when I get it done.

Huh? how do you know it has R32 GT-R wastegate springs?

Engine might have been rebuilt with thicker headgasket. Maybe it has different pistons/cams/etc. Or maybe gauge isn't accurate *shrugs*

[Meathead]

Only way to know condition of piston/bore/valves is to do a leak down test regardless of cams and any other mods.