Jump to content
SAU Community

Recommended Posts

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? :))))

Link to comment
https://www.sau.com.au/forums/topic/369488-rb25-det-neo-just-forged-it/
Share on other sites

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?

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 :mellow:

Edited by aleks

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

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 by Rolls

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..

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 by JonnoHR31

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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • I can get more photos of it here soon and I plan to make a thread detailing the process. I received the car this way and it sorely needs refinishing. That is probably the most appealing photo of it. Up close it is fading, cracked, and needs to be re-glued. Depending on their condition I'm on the fence between refinishing or making a new set.  Another angle hiding the pimples and razor pumps  
    • According to this thread the RS4V with build plate RC40 comes with the R200 diff @ 4.083 ratio as well (mine has said RC40 denotation). We may need to check if the axle stubs are the same pattern as well. The auto subframes have longer axles. However I think yours being a later Series 2 as well, we should have the same bolt pattern for the diff stubs. Unless your upgraded rear also has upgraded axles. Either way, I would not be opposed to pulling the covers to check so I can inspect that  fancy rear core  Also I don't have HICAS. I don't believe that should change things but I hope the people here with heaps more experience than me can correct me if I'm wrong   Let me know if you want to attempt to make this work and I can get some pictures of mine from under the car. 
    • It's not that straightforward. For example I have had this code because my ignitor/power transistor wires were unplugged. It knows something is wrong but has no idea what it means. If you want to actually diagnose this I recommend following the service manual flowchart for code 21. Ohm out the harness, coilpacks, inspect the ECU, etc. And again, it's entirely possible for there to be no problem at all but if you're running a different coilpack it'll trigger the code because it doesn't like what it sees.
    • If it (the code) wasn't still current, it should have gone away by itself by now. No, nothing it 10/10. But it is quite likely. Everything else to do with the ignition could still be responsible (which is wires and connectors). The car is an old piece of shit now, so all the wires and connectors are also old pieces of shit.
    • Lock me in mate, although I'm not sure if I'll be heading up from Goulburn or down from Sydney, either way, return will be back to Goulburn 
×
×
  • Create New...