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Low Compression Rb26, 356.9 Hp In 4wd Dyno In 1bar

Midnight Racer

By Midnight Racer,
in Engines & Forced Induction

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Midnight Racer Rising Star

Midnight Racer

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Posted (edited)

my gtr in 4wd dyno on 11th December and run 356.9 hp in 1 bar with bp98 ( Notice A/F Ratio is 10.4, very rich fuel).

when engine install, the compression test is ONLY 80, 85, 100, 100, 85, 85. It is very low compression.

engine detail is new re-build head with hks 256cams and hks valve spring, new valve. stock bottom end.

turbo is custom made. idel is 1000 rpm, very smoothly.

what problem will cause low compression?? valve bent or piston crack or piston ring or something else??

If it is the valve problem, can we see it from dyno?? I really want to know where is the problem.

thanks help.

post-11001-1165994282.jpg

Edited by Midnight Racer
Midnight Racer Rising Star

Midnight Racer

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Posted
  B-Man said:
How was the compression test done ? Hot / Cold ? Wet / Dry ? Has the compression tested been calibrated ?

test done by cold/ wet/ dry. I add 10ml in each cylinder and same result.... :laugh:

my friend's r32 gtr engine compression test is 150,150,155,155,155,150 when cold/dry)

DVS JEZ Grand Master

DVS JEZ

Posted
Posted
  Midnight Racer said:
yes, I want to know what problem with my rb26. head problem or bottom end.

already check gasket and no leaking, but vacuum is low...

if wet and dry are the same then bottom end is ok, sounds more like valves, try a leak down test,

do you have much blowby?

MR331307 Experienced

MR331307

Posted
Posted
  Midnight Racer said:
my gtr in 4wd dyno on 11th December and run 356.9 hp in 1 bar with bp98 ( Notice A/F Ratio is 10.4, very rich fuel).

when engine install, the compression test is ONLY 80, 85, 100, 100, 85, 85. It is very low compression.

engine detail is new re-build head with hks 256cams and hks valve spring, new valve. stock bottom end.

turbo is custom made. idel is 1000 rpm, very smoothly.

what problem will cause low compression?? valve bent or piston crack or piston ring or something else??

If it is the valve problem, can we see it from dyno?? I really want to know where is the problem.

thanks help.

cause of this can be rings or burnt valves

Blitz Grand Master

Blitz

Posted
Posted

Hang on, in your for sale thread you mentioned that your "tuner" ran the car up at 266awkw with an AFR of 15.2

  Midnight Racer said:
After 3 months re-build, this morning my car doing dyno run for final tune in F.I.S.T. in brisbane.

unforyunately, cylinder# 1 was piston crank in dyno when they adjustable A/F ratio from 15.2 to 14.3... :O

before running in dyno today was 266awkw at 4 wheels in A/F ratio 15.2 ( too rich fuel) with 1 bar boost.

So which is it?

Sounds like you got fisted hard by 'F.I.S.T'

Midnight Racer Rising Star

Midnight Racer

Posted
  • Author
Posted (edited)
  Blitz said:
Hang on, in your for sale thread you mentioned that your "tuner" ran the car up at 266awkw with an AFR of 15.2

So which is it?

Sounds like you got fisted hard by 'F.I.S.T'

THIS IS MY MISTAKE BCZ I DO NOT KNOW AFR ON 11/12, I APOLOGIZE AND CLOSED IT.

SORRY, I do not want to fist hard for anyone, especially F.I.S.T. they were just tuner, not engine builder. no body know what will happen in dyno. I try to find out what problem for my engine bcz I already try to re-build again !!. If problem form head, I can sent it back to my head builder bcz it still have repair guarantee.

that's my mistake bcz I do not know about AFR until 12/12 I got dyno result. 11/12 my builder told me my engine broken one cylinder in dyno, when tuner try to adjustable AFR . This is the history:

I tow my car back on 12/12 and saw dyno result . the compresstion test was done on 04/12. we do not understand why so low compression and sent to F.I.S.T. to dyno check on 05/12. they said the in the dyno test engine looks good. I tow my car back on 07/12 and fixed the idle problem. then sent back again to tune. ths result I got was the 6th run, then engine broken in dyno........ :dry:

13/12 done compression again in cold/dry, the result is 0, 85,100,100,85,85.

NOW I JUST WANT TO KNOW WHY IS SO LOW COMPRESSION. I DO NOT WANT SAME PROBLEM BCZ NOW I START TO TRY RE-BUILD IT AGAIN.

Edited by Midnight Racer
Midnight Racer Rising Star

Midnight Racer

Posted
  • Author
Posted
  sewid said:
Those compression test results and AFRs are fine if you happen to live in bizzaro world. You didn't specify if you did in the first post so i thought i'd check.

My first post is my mistake bcz I do not understand AFR. THAT IS MY MISTAKE.

But If ur engine's compression is 85,85,100,100,85,85. would u think IT IS GOOD??????????????

I do not argue anyone, just want to find out what 's wrong with my engine, ok?? I do not want have same problem when some one re-build it again.

r3240sx Enthusiast

r3240sx

Posted
Posted

Dont rebuild your engine again unless you have probable cause to do so.

I thought I blew a headgasket, turned out to be something totally different... But in the process of diagnosing it I compression tested my motor. At wide open throttle when the motor was cold I got 80/80/80/85/85/80 on my RB20. There is no way I have EVENLY ruined my pistons on every cylinder. You need to look for even numbers, not the right numbers according to your buddies test. If the numbers are all even, chances are you're fine, and if they read low, its either how you're testing, or the guage. If they are dramatically different (ones really low, ones not) then you should be worried.

Do the test a few more times. See if the guage will read any higher. Try a different guage. If no changes, then I say dont worry about it.... you seem to be making some decent power, no?

With supposedly 80 psi compression in each of my cylinders, my motor has lost no power since it read 150 psi on all.... hmmmm....

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