Rb25 Det Neo , Just Forged It

[avoiee]

So finished rebuilding the engine , got Arias custom made pistons in it for neo engine ! when it was freshly finished it showed 120, 120, 130, 125, 130, 120 psi in all six cilinders . drove about 700km and now in all 6 cilinders is 120psi, same in all!! i have putted tomei poncams as well ! gasket is standard size standard has 9:1 as far as i know what number i have now? is it too low?

my friend owns RB26 he did same (forged it) and his car shows 145psi in all six?

so am i ok or in trouble? )))

[r33_racer]

Normally bigger cams will drop your compression when you do a test, in comparison to standard. But not that much, especially with poncams. Did you build it yourself or an engine builder do it for you?

You did have the throttle fully open when you did the test?

[Simon-S14]

my healthy neo with pon cams reads 100 psi all round lol

[johnbarry88]

as long as all cylinder are even theres nothing to worrie about

[aleks]

my healthy neo with pon cams reads 100 psi all round lol

This is why I was persistently asking you about this.

110psi across all six here, with a new engine with poncams which I thought was pretty low but it runs great.

Using the same tester on an a standard RB26 which had 165-170psi across all cylinders then a built RB26 with big cams; 160-165psi

Edited June 30, 2011 by aleks

[STATUS]

my healthy neo with pon cams reads 100 psi all round lol

Hmmm generally they are around 140psi on a healthy stocker.

[Simon-S14]

Hmmm generally they are around 140psi on a healthy stocker.

yeah its low. think its my works comp tester i used that is a bit on the flogged side.

[Simon-S14]

if it runs great then dont worry to much about it. as long as they are all even and witin 5 psi of each other

[Rolls]

and make sure it isn't burning oil

[urtwhistle]

hmm my Rb3025 came up with 155 and all the rings were lined up lol

[avoiee]

Normally bigger cams will drop your compression when you do a test, in comparison to standard. But not that much, especially with poncams. Did you build it yourself or an engine builder do it for you?

You did have the throttle fully open when you did the test?

didn't touch the throttle and didn't cut the fuel lol i'll try to do that way

Glad that here is people running that low CR with no problems:)

thx

[AngryRB]

Hmmm generally they are around 140psi on a healthy stocker.

you sure?? cause mine is as high as 170 and 175,

100psi is low, that must be pretty unresponsive on low revs??

[Rolls]

you sure?? cause mine is as high as 170 and 175,

100psi is low, that must be pretty unresponsive on low revs??

I really doubt its compression is actually almost half of yours, if it did it would drive like absolute shit, either completely wrong pistons or blown rings. The reality is it is probably one motor was cold/hot, different tester, different rpm, different cams etc.

My old rb20 measured 90-95 on all 6, made 155kw on 11psi stock turbo and blew no smoke, all that matters is it is close.

Edited June 30, 2011 by Rolls

[Simon-S14]

thats just it.. too many variations to be able to compare one to another.. the main thing is all cyns are the same, and comp testers fall into the same bucket as dynos.. just a tool.

[AngryRB]

thats just it.. too many variations to be able to compare one to another.. the main thing is all cyns are the same, and comp testers fall into the same bucket as dynos.. just a tool.

well i wouldnt be happy them just all being the same, id want to know its perfect after spending all that money rebuilding an engine,

a compression guage shouldnt be more than 5% different to the next , thats like saying a tyre guage says its 40psi but another is saying 30psi?

must be quite a big gap with forged pistons when there cold and the cam must be quite long duration to justify a 70psi drop after a rebuild, but just my opinion,

but if your happy with it then great..

[DVS JEZ]

Dont forget, cam timing can have a major effect on compression test results

[Kenna802]

My New motor has 145 across all six. Seems to blow smoke when cold but all good when warm

[JonnoHR31]

thats like saying a tyre guage says its 40psi but another is saying 30psi?

actually happens a lot more than you'd think and more than 10psi a lot of the time, especially at servo gauges

also dont forget, static compression is different to dynamic compression, way too many variables to go comparing readings. as said aslong as they're all within 5-10psi and its not using more oil than fuel its fine.

Edited July 3, 2011 by JonnoHR31

[Rolls]

well i wouldnt be happy them just all being the same, id want to know its perfect after spending all that money rebuilding an engine,

a compression guage shouldnt be more than 5% different to the next , thats like saying a tyre guage says its 40psi but another is saying 30psi?

It isn't just the compression gauge though, it is cam timing, actual compression ratio due to pistons, if they are forged, if they rings aren't yet bedded in, if you have a big cam, all of these will change the compression.

[Bl4cK32]

when it was freshly finished it showed 120, 120, 130, 125, 130, 120 psi in all six cilinders .

before or after it was run in, and has it been tested both hot and cold, wet and dry?