Rb26 Compression Question

[portaz]

Hi guys I'm pretty sure I need to rebuild it but I thought it worth asking the question. Last week I was about to race at Sydney dragway but I thought maybe I should do a compression test as I hadn't done one since fitting turbos. Cyl 1 to 5 were 150psi and #6 was 100psi wet or dry, the engine had been run that day but wasn't at operating temp. It doesn't use oil and still goes as good as it did at the skyline drag day where it ran 12.1 at 118mph. So I'm wondering if there is another test? I disconnected the cas and turned it over to listen for any difference while cranking but it sounded the same on each cylinder. Before I changed turbos I also attended a Wednesday night where the coil packs gave up and that's the only time I can think of anything actually going wrong with the car, but since then it's been dyno tuned and done at least 10 passes, is that possible with one cylinder 50psi down? Or am I just clutching at straws and need to rebuild it ?

Scott

[Moodles2]

Headgasket maybe?

[GTR260]

That is outside the allowable limit, could be a blown head gasket, im no expert. Have u checked ur radiator, plugs?

[portaz]

Plugs are even and perfect, radiator green no oil andoil cap perfect too

[The Dan]

Sounds like it might be a valve problem. You need to do a leak down test

[portaz]

I assume there is special equiptment needed for leak down test? So more likely valves than rings?

[zac320]

I believe u can tip a bit of oil into the cylinder and if compression doesn't increase it's your valves

Correct?

[The Dan]

Am I the only one who read his entire post?

He did a wet test

[portaz]

Yes wet only on number 6 though and there was no difference at all, if it's valves wouldn't it run badly though? Thanks for all the input guys I appreciate it.

[SiR_RB]

if compression didnt increase with oil in the cylinder then valve probs'

get a leak down test to make sure like stated...

[portaz]

Hi guys just a quick update I decided to do hot compression test to see if there was any improvement and I did #5 and got 145 and #6 and got just over 140 with both I did for above 10 secs on starter I didn't bother checking the others as previously on the cold test they were even, so what does this mean? I'm looking at installing my -5s and 1000cc injectors and e85 but I don't want to waste time if the engine needs to come out, any opinions are appreciated. Scott

[KiwiRS4T]

Listen to the advice. Do a leakdown test.

[SiR_RB]

Hot dry test 145 and 140psi? Seems like a tired engine....boost it up should be right ! Haha

[SiR_RB]

Hot dry test 145 and 140psi? Seems like a tired engine....boost it up should be right ! Haha

[portaz]

I don't have a leak down tester that's the only reason I havnt done it yet, are they expensive ?

[AngryRB]

  On 15/12/2012 at 3:49 AM, SiR_RB said:

Hot dry test 145 and 140psi? Seems like a tired engine....boost it up should be right ! Haha

if he had some aftermarket cams, 140psi might be perfectly normal, and now there close in comparison compared to the original 50psi difference in number 6, and doing 12 second quarters it must be pretty healthy..

[portaz]

Stock cams but yavuz went pretty aggressive with cam timing he said he doesn't usually go that far but it kept wanting more when it was tuned

[SiR_RB]

Cam gear timing or ignition timing?

What power you making at wheels?

[Deano 1]

If your worried its the cam timing, mark where the cams are ATM. Than move them both back to 0 test the comp and see if there's a diffrence.

Than just set the cams back to the marks you made before you drive the car again.

[portaz]

Sorry I meant cam gear adjustment it has hks gears and its never been changed since it was tuned more than a year ago so I have no reason to think that has anything to do with it, it has 290kw at the rears but was limited due to afms still being stock but he said it made the power very easily,