Jump to content
SAU Community

Recommended Posts

125psi is pretty low.

the figures seem TOO close together. if they were that low i would think there would be small variances of 3-5psi between them at least. thats my opinion rather than expert advice so just get another one done somewhere else.

I tested mine when dropping the new injectors in, it runs wiseco forged pistons that have been setup on the looser side so they do slap a tad when cold.

When I finally got around to testing the comp ratio the motor had done around 20,000km's, wasn't using any oil.

To my suprise ALL cylinders were equal apart from cylinder 3 that read 1psi different. :D

I got 153psi or there abouts I don't remember exactly but it was around the mid 150's.

So when warm and the pistons fill the bore a little better no doubt I will receive a higher reading.

So yes, equal values in every cylinder is possible. :dry:

  • Replies 50
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

it is possible, but at the 125psi level you'd probably start to get figures that arent so close together, let alone exactly the same.

Yes for such a low level, but it may just be the guage. Which is why the general rule is to go off variation.

Cam timing could also be out, maybe rebuilt some time with lower comp pistons, thicker headgasket.. Could be a number of things.

My Rb20DET with std cam timing saw 145psi in all cylinders, that was at 60,000km's. Cam timing does make a difference to the comp ratio.

ok, is your car still running fine?

using oil?

what do people think about this?

Beef

It is running pretty good for a 5 cyl but using a bit of oil...

i put about a litre of lucas in it on the weekend and she is running good again.

It still boosts and goes hard.. emm did i mention that it smokes a shitload!! :P

It only has to last me a few more weeks till i drop a RB25 in her.. then i will re-build the RB20 to sell.

Cam timing could also be out, maybe rebuilt some time with lower comp pistons, thicker headgasket.. Could be a number of things.

Cam timing does make a difference to the comp ratio.

oh ok, well im pretty sure that the timing was on 22degrees when comp test was done, i have taking it back to 20degrees, so maybe it may be a litle lower/higher this time?

which way?

Tim

Um, cam timing, not ignition timing. If you want to check the cam timing you need to take the belt cover off & check that the marks on the belt match the marks on the pulleys.

oh sorry, ha ha

how would one go about adjusting the cam timing.... can it be adjusted or do i need to get another timnig belt or something?

Beef

OK just went and got the compression re-tested.....

1. 145psi

2. 150psi

3. 150psi

4. 145psi

5. 150psi

6. 150psi

so i dont know what the other F**K head was doing, maybe he tested when cold or something....

so does this sound like a better number....

maybe it will improve when i do the oil change that is past due..... and also flush it out..

what you think...

check the pic, its my baby gettin checked... :P

compcheck.bmp

Nothing wrong with 150psi odd.

It was probably just the other bloke guage and or didn't give it wide open throttle.

or... maybe he wanted to rebuild your perfectly fine engine. :D

OK just went and got the compression re-tested.....

1. 145psi

2. 150psi

3. 150psi

4. 145psi

5. 150psi

6. 150psi

so i dont know what the other F**K head was doing, maybe he tested when cold or something....

so does this sound like a better number....

maybe it will improve when i do the oil change that is past due..... and also flush it out..

what you think...

check the pic, its my baby gettin checked... :P

Nothing wrong with 150psi odd.

It was probably just the other bloke guage and or didn't give it wide open throttle.

or... maybe he wanted to rebuild your perfectly fine engine. :P

yeah maybe he wanted to make himself a few extra bucks.... but to eliminate teh chance of a dodgy mechanic i actually watched them do it and saw the results with my own eyes...

oh and..... what you mean by they probably didnt give it wide open throttle, they dont start the engine, they only turn it over 4 times....... its never actually running.....

Beef

oh and..... what you mean by they probably didnt give it wide open throttle, they dont start the engine, they only turn it over 4 times....... its never actually running.....

Beef

Ofcourse it wont start the engine, it has no coils or spark plugs - what he means is that the throttle is flat to the floor. Apparently this is the correct way to do it, otherwise you will get incorrect readings.

Ofcourse it wont start the engine, it has no coils or spark plugs - what he means is that the throttle is flat to the floor. Apparently this is the correct way to do it, otherwise you will get incorrect readings.

um der freddy........

the way he said it sounded like he was talknig about a dyno test or something.....

WOT will allow air to enter the cylinder easier and free'er which is why the results are more accurate. not doing the test at WOT may give you readings of 10-15psi less which is what i've noticed in the past.

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 time is always correct. Only the date is wrong. It currently thinks it is January 19. Tomorrow it will say it is January 20. The date and time are ( should be ! ) retrieved from the GPS navigation system.
    • Buy yourself a set of easy outs. See if they will get a good bite in and unthread it.   Very very lucky the whole sender didn't let go while on the track and cost you a motor!
    • Well GTSBoy, prepare yourself further. I did a track day with 1/2 a day prep on Friday, inpromptu. The good news is that I got home, and didn't drive the car into a wall. Everything seemed mostly okay. The car was even a little faster than it was last time. I also got to get some good datalog data too. I also noticed a tiny bit of knock which was (luckily?) recorded. All I know is the knock sensors got recalibrated.... and are notorious for false knock. So I don't know if they are too sensitive, not sensitive enough... or some other third option. But I reduced timing anyway. It wasn't every pull through the session either. Think along the lines of -1 degree of timing for say, three instances while at the top of 4th in a 20 minute all-hot-lap session. Unfortunately at the end of session 2... I noticed a little oil. I borrowed some jack stands and a jack and took a look under there, but as is often the case, messing around with it kinda half cleaned it up, it was not conclusive where it was coming from. I decided to give it another go and see how it was. The amount of oil was maybe one/two small drops. I did another 20 minute session and car went well, and I was just starting to get into it and not be terrified of driving on track. I pulled over and checked in the pits and saw this: This is where I called it, packed up and went home as I live ~20 min from the track with a VERY VERY CLOSE EYE on Oil Pressure on the way home. The volume wasn't much but you never know. I checked it today when I had my own space/tools/time to find out what was going on, wanted to clean it up, run the car and see if any of the fittings from around the oil filter were causing it. I have like.. 5 fittings there, so I suspected one was (hopefully?) the culprit. It became immediately apparent as soon as I looked around more closely. 795d266d-a034-4b8c-89c9-d83860f5d00a.mp4       This is the R34 GTT oil sender connected via an adapter to an oil cooler block I have installed which runs AN lines to my cooler (and back). There's also an oil temp sensor on top.  Just after that video, I attempted to unthread the sensor to see if it's loose/worn and it disintegrated in my hand. So yes. I am glad I noticed that oil because it would appear that complete and utter catastrophic engine failure was about 1 second of engine runtime away. I did try to drill the fitting out, and only succeeded in drilling the middle hole much larger and now there's a... smooth hole in there with what looks like a damn sleeve still incredibly tight in there. Not really sure how to proceed from here. My options: 1) Find someone who can remove the stuck fitting, and use a steel adapter so it won't fatigue? (Female BSPT for the R34 sender to 1/8NPT male - HARD to find). IF it isn't possible to remove - Buy a new block ($320) and have someone tap a new 1/8NPT in the top of it ($????) and hope the steel adapter works better. 2) Buy a new block and give up on the OEM pressure sender for the dash entirely, and use the supplied 1/8 NPT for the oil temp sender. Having the oil pressure read 0 in the dash with the warning lamp will give me a lot of anxiety driving around. I do have the actual GM sensor/sender working, but it needs OBD2 as a gauge. If I'm datalogging I don't actually have a readout of what the gauge is currently displaying. 3) Other? Find a new location for the OEM sender? Though I don't know of anywhere that will work. I also don't know if a steel adapter is actually functionally smart here. It's clearly leveraged itself through vibration of the motor and snapped in half. This doesn't seem like a setup a smart person would replicate given the weight of the OEM sender. Still pretty happy being lucky for once and seeing this at the absolute last moment before bye bye motor in a big way, even if an adapter is apparently 6 weeks+ delivery and I have no way to free the current stuck/potentially destroyed threads in the current oil block.
    • Literally looks like direct port nitrous haha
×
×
  • Create New...