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Rb26 Compression Question

portaz

By portaz,
in Engines & Forced Induction

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portaz Mentor

portaz

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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

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  • 3 months later...
portaz Mentor

portaz

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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

AngryRB Grand Master

AngryRB

Posted
Posted

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..

Deano 1 Mentor

Deano 1

Posted
Posted

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 Mentor

portaz

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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,

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