Jump to content
SAU Community

Recommended Posts

Dont know if this really counts as performance or maintenance but i will put it in here anyway.

I had a compression test run on the R33 RB26DETT thats in my ceffy. Now most readings from a brand spankin new RB26 are about high 160+ or Low 170s or something.

Now i know when u do cam work and pistons and stuff that it will change the reading u get... BUT... will it change it so drastically that it would read 125psi across all 6 sylinders????

Can u guesstimate from that reading whats been done or not?

Link to comment
https://www.sau.com.au/forums/topic/54124-compression-test-readings/
Share on other sites

The main thing I'd be looking at is the variation between cylinders. If you've changed cams and cam timing then the reading are going to change, and sometimes drastically. The variation will tell you if one cylinder has done a ring land or has a bad bore etc. The only time this doesn't apply is when you've blown all the ring lands or fried all the rings, but this will be evident in other ways!

Yep as the others said, variance is definitely more important because the absolute readings of every gauge are different. I would try disabling the injectors as I found they deflated the readings by upto 10psi. So pull the fuse to the ECU or disconnect each injector if its accessible! Oh and, dont forget to have all 6 sparkies out when you do it, and also have the throttle wide open!

As long as its fairly even across all the cylinders they should be right. Should vairy about 1 - 3 psi max each cylinder.

 

:wave:

Jun

1-3psi max?

have you tested 8 year old motors which put out readings that close to each other?

i was thinking more along the lines of 1-13 :wave:

what guage do u use? guages i have used u cant even see 1psi difference lol.

1-3psi max?

have you tested 8 year old motors which put out readings that close to each other?

i was thinking more along the lines of 1-13 :D

what guage do u use? guages i have used u cant even see 1psi difference lol.

If your getting 13 psi difference usally indicates you are losing a bit of compression with worn out ring lands and it will only get worse....

eg: testing RB25

Piston 1 - 160psi

Piston 2 - 163psi

Piston 3 - 162psi

Piston 4 - 161psi

Piston 5 - 162psi

Piston 6 - 150psi - Doesn't look to good!

Maby you can get away with a little more slack but on an old engine you carn't have 1 cylinder down a fair bit eg 13psi down and the rest fairly even :D It can result in time for a rebuild.

Not sure on what guage it was but just compression test.

Had one RB25 with cylinder number 6 on 0psi compression !!! :headbang: - I dont know how the thing started, it ran like a hairy goat :uh-huh:

:D

Jun

cameron, most readings i have seen are more random than that! ie there not one cyl that is way out compared to the rest, they are all a few psi diferent from each other....and yeah cyl 6 usually lower (first to get damaged)

could be the head though (burnt valves etc) which means a lot less to fix than bottom end and i would even bother because it probably wouldnt be noticeable if there was a diff of say 8-10 psi in one cyl..

in relation to the ceffy, like cam said, if they are even readings and it makes good power dont worry about it at all... if anything do a leakdown test to double check.

guages/cranking speed/battery/auxilaries etc all make sure you will never get a reading like new unless you are just lucky and the guage reads high..

If your getting 13 psi difference usally indicates you are losing a bit of compression with worn out ring lands and it will only get worse....

 

eg: testing RB25

 

Piston 1 - 160psi

Piston 2 - 163psi

Piston 3 - 162psi

Piston 4 - 161psi

Piston 5 - 162psi

Piston 6 - 150psi - Doesn't look to good!

 

Maby you can get away with a little more slack but on an old engine you carn't have 1 cylinder down a fair bit eg 13psi down and the rest fairly even :D It can result in  time for a rebuild.

 

Not sure on what guage it was but just compression test.

 

Had one RB25 with cylinder number 6 on 0psi compression !!! :headbang: - I dont know how the thing started, it ran like a hairy goat :uh-huh:  

 

 

:D

Jun

your kidding right?It did have 5 other cylinders to push it along you know....

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

    • The cross sectional area of a circular hole scales with the square of diameter. So a 2mm diameter hole is 4x the area of a 1mm hole. Not double. The 1.7mm hole is nearly 3x the area of a 1mm hole. You do not need restrictors at both ends of the oil supply line. If you have new, additional restrictors at the turbo end, that you did not have before, then you do not need a restrictor at the inlet end.
    • Hi all. Been a while but things are moving along. I just have something that I am wondering about. Since I will use OEM turbo oil pumbing, I got myself a new bolt, the one that goes into the engine block oil feed. As I recall (and see visually) this bolt comes restricted with I think a 1.7mm hole? Not quite sure but it was something around that size. The turbos have 1mm restrictor bolts installed, as necessary due to ball bearings and my higher oil pressures. Can I now just use that OEM bolt with the 1.7mm hole in for the engine block or will this actually be too much oil flow restriction and I have to drill it out first? In my head it would make sense for the bolt to be at least 2mm wide as both turbos take "1mm of oil flow". Do let me know if my logic is flawed here, I just want to make sure I don't kill my turbo bearings with too little oil. Don't know if I can trust the saying I read somewhere that ball bearing turbos essentially only need an oil mist
    • There are several aftermarket options available, from not-too-painful moneyhttps://justjap.com/collections/driveshafts-bearings/products/d-max-reinforced-replacement-rear-driveshaft-set-fits-nissan-s13-s14-s15-r32-r33-r34-c35 and  https://justjap.com/products/crank-motorsport-billet-rear-axles-fits-nissan-skyline-r33-gts-t-r34-gt-t?srsltid=AfmBOorQk4xkGUa98kO7v2ePLUiNt-HRrM2AwWNw9mbSIVE1ujBVwY__, all the way up to The Driveshaft Shop https://driveshaftshop.com/skyline-cv-axles/
    • Yeah based on old XRC5964S specs, it looks to be roughly GTX3576R sized? But this 5964S compressor will flow 90lb airflow somewhat similar to the compressors in both the GTX3584RS or G35-1050.. I fully expected the 0.64 rear A/R to choke up top - seems way too small from typical convention - but these are seemingly beneficial over the prior 0.82 results.. Be interesting to see if he comments on the EFR question in that thread - he mentioned in a prior video that BW EFR's were the "cats pajamas 10 years ago", but by the sounds of things all his kits have been using Xona for quite a while now.
    • Yeah it’s still got the oem manual gearbox and clutch, only kinda mods are a blow off valve, coil overs, and a aftermarket intercooler. Also had it for about 2 months now with a lovely midnight purple paint on it.
×
×
  • Create New...