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Compression test results on RB20... Help!

Ed G

By Ed G,
in Engines & Forced Induction

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R31Nismoid Grand Master

R31Nismoid

Posted
Posted
how many rev's have you tested it at its maby a good thing to count them as cheep comp testers keep presuring up and down as thier internals arnt so great in conclusion your test readings are not so bad if say in cylinder 1 you did 7revs and 4 did 5revs this could be your issue also warm your engine up before hand it will make a diffrents

what? you turn it over to compression.

so they all will be the same

wrxhoon Grand Master

wrxhoon

Posted
Posted

Wwhen you put oil in the cilinders the compression will rise for 2 reasons :

1) the oil will make the combustion chamber smaller , so you are compressing same volume of air into a smaller area .

2) the oil stops compression going through the rings .

You only pour oil in the cils if you have low compression in one or more cils ( like 30 %- 50 % less than the others ) , then you pour oil in there to determine if its valves or bottom end .

If compression doesn't rise quite a lot its valves , if it does rise a lot then its rings usualy .

A better test is a leakdown test , thats what you should be doing if you have a leakdown tester .

Ed G Grand Master

Ed G

Posted
  • Author
Posted

Ok, did warm test, but my bro dropped the comp tester before we started ( :goddam: ) so the results may not be accurate!

1 - 145

2 - 145

3 - 145

4 - 145

5 - 145

6 - 150

Also cleaned the AFM and when gapping the plugs found one that was stuffed! Hopefully that is responsable for my miss!

As to the crappy idle, it's better but sill not good :cuss: it still hunts wont settle, but not as bad as before (I also found a vaccume leak)... so will need to check it out more!

grigor Rising Star

grigor

Posted
Posted

What's the first thing you thought when you saw those numbers?

Head gasket between 4 and 5.

Are you planning on big horsepower, lots of mods, then you might have a problem.

But it's done 120K's (at least) it runs nicely and will probably go for years. That's the hassle with Rb20's they're getting old and you have to weigh up their cost against a newer Rb25.

My latest Rb20 had 119k, runs sweet enough but has one weak cylinder. I've done about 100k since with only routine maintenance and it's still fine.

If I was to go mad with boost, it would probably die, so ultimately it's up to you.

Regards.

superspit Mentor

superspit

Posted
Posted

well done Ed G, nice figures! (hope u r feeling better now!!)

I really believe you'll find a small 'air/vac' leak soon,... I'm learning how much these motors won't tolerate the slightest escape/introduction of air.

Aren't your fellow Skliner's just ace?

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