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Chris Prak
DieHard
WA
JZZ30 Soarer - Twin Snails

Posts: 855
Reg: 12-2006

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Wednesday, July 21, 2010 - 05:35 pm, by:  Chris Prak (Carizma) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Okay guys, some of you may know about my saga but anyway, did a compression test today.

Tested dry, with the throttle closed, with a screw-on type tester and cranked until the needle on the gauge would not move no more (about 4-5 cranks). The results:

1- 80
2- 90
3- 115
4- 85
5- 95
6- 135

I didn't bother doing a wet test as I believe they will only tell if it's the valves or rings that are the culprit and as I won't be rebuilding, theres no point figuring out which one it is.

So I'm pretty confident in saying, I need another motor? Oh well number 3 on its way...
Matt Sartori
DieHard
Western Australia
Rx7

Posts: 757
Reg: 08-2008

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Wednesday, July 21, 2010 - 05:46 pm, by:  Matt Sartori (Klutch) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Ive always been told to do it throttle open, but those figures still sound quite low... ill let someone with a bit more knowledge say for sure though


how do you keep on killing them!?
Chris Prak
DieHard
WA
JZZ30 Soarer - Twin Snails

Posts: 856
Reg: 12-2006

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Wednesday, July 21, 2010 - 06:22 pm, by:  Chris Prak (Carizma) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

It's not completely shut when the throttle is closed, and I also thought the ISCV is used to for start-up anyway which bypasses the throttle body. Besides, if I got 135 out of cylinder 6, it's safe to say it's getting enough air to compress.

I don't kill them, they commit suicide because they fear my right foot.
Ned Lodge
Tinkerer
QLD
TT

Posts: 8
Reg: 07-2010

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Thursday, July 22, 2010 - 03:50 pm, by:  Ned Lodge (Deadly_nedly) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I recently have done some compression testing:

Screw in compression tester.
ECU fuse out.
Throttle fully open.
Dry cylinders.
6-7 crank overs, needle jumps each time.

Needle reads a minimum of half the final PSI on the first crank.

Lowest cylinder 188 PSI. Highest cylinder 195 PSI = 3.6% difference.

I have read that there should be no more than 10% difference over all cylinders.

This is a calculation I have got from:
http://www.pumaracing.co.uk/comp.htm

Cranking pressure (psi) = CR^1.3 x 14.7 x 2/3
CR^1.3 is the Static Compression Ratio raised to the power 1.3

So I calculate that with the Soarer CR @ 8.5:1
the ideal PSI should be 158.3 PSI.

Which also made me question why is mine so high?

I have not completed a "Wet" test. Possibly that is what you should do next Chris.

This will help in identifying issues with particular components such as rings & valve stems.
Scott Wilkes
Goo Roo
Tasmania
92 TT Factory Manual, 70 HG GTS Monaro

Posts: 1680
Reg: 10-2008

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Thursday, July 22, 2010 - 06:12 pm, by:  Scott Wilkes (Scottywilkes) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

ive got 195psi over all cylinders using my snapon compression tester, throttle closed, 5 revolutions :-)
James Wilson
TryHard
sa
TT

Posts: 297
Reg: 10-2008

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Thursday, July 22, 2010 - 06:16 pm, by:  James Wilson (Ser493) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I think really when it comes down to it you are after consistency between all cylinders. With in reason 85psi is very low.
Chris Prak
DieHard
WA
JZZ30 Soarer - Twin Snails

Posts: 857
Reg: 12-2006

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Thursday, July 22, 2010 - 07:30 pm, by:  Chris Prak (Carizma) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Thank You very much for that Ned. Great info!

I'm not going to bother with a wet test as the readings are too shocking to even bother fixing as I'm not after a rebuild right now. If I ever do rebuild, I will slowly build the current motor... though in the meanwhile, a second hand motor will suffice.

The current one doesn't even start, even though we have spark and fuel.
Ned Lodge
Tinkerer
QLD
TT

Posts: 9
Reg: 07-2010

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Friday, July 23, 2010 - 05:54 am, by:  Ned Lodge (Deadly_nedly) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Chris, your motor definitely seems sad. I would be interested to see the results of a "wet" test on your engine.

It would also provide that little extra information on this thread.

-------

Scott, did you test the same method as me, as I would like to confirm my method with yours.

Thanks.
Guy Moore
TryHard
QLD
JZZ30 TT M/T

Posts: 113
Reg: 03-2010

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Friday, July 23, 2010 - 07:33 am, by:  Guy Moore (Thesoarerguy) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

I tested mine with screw type tester dry test no throttle and my spark plugs were still in the coil pack. I got

1. 148
2. 145
3. 150
4. 148
5. 150
6. 150

which I didn't think was too bad considering there's only 5% difference between them all.
James Wilson
TryHard
sa
TT

Posts: 298
Reg: 10-2008

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Friday, July 23, 2010 - 07:54 am, by:  James Wilson (Ser493) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Thats only like 5psi... Good result.
Guy Moore
TryHard
QLD
JZZ30 TT M/T

Posts: 115
Reg: 03-2010

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Friday, July 23, 2010 - 09:58 am, by:  Guy Moore (Thesoarerguy) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

not bad for 150000 on the clock
Tim Ross
Goo Roo
Qld
1J + GT35-82R

Posts: 2337
Reg: 09-2007

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Wednesday, May 11, 2011 - 01:40 pm, by:  Tim Ross (Retox) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

mine just got done - 202000kms

1. 160
2. 160
3. 160
4. 160
5. 160
6. 155

Needless to say I'm pretty happy with that.

Anyone know what a 1JZ would have been reading brand new from the factory?
Matthew Sharpe
Goo Roo
North Island
JZZ31

Posts: 6353
Reg: 10-2005

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Thursday, May 12, 2011 - 06:17 am, by:  Matthew Sharpe (Madmatt) Quote hilighted text Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

You can calculate maximum theoretical compression from cylinder volume and compression ratio - unfortunately I'm too sick this morning to apply myself to the problem And of course even a brand new engine doesn't give maximum compression.

Your figures look pretty good - well cared for motor there to go that long and still be so healthy

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