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Old 11-21-2005, 11:07 PM   #1
tino
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Default What is the standard compression test values on a 2.5ltr with forged pistons

hey guys,

Ive got a 2.5ltr with forged pistons and rods.. i had a compression test done at one workshop..

got 110, 90, 120, 95 and a leakdown of 50%


However i took the car to another workshop and got 130 for the rears and 135 for the fronts..

What value are they suppsoed to be? i was told around 160 but that was for a 2.0ltr is there any difference in the 2.5ltr with FORGED pistons...

The workshop that built the engine said that it should be around 140 and they gave me the figures of 130, 135... They think that the engine is fine and didnt think that a leakdown was warranted? What are ur opinions?
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Old 11-21-2005, 11:14 PM   #2
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I did a comp. check with 800 miles on my rebuilt motor with CP pistons. I had 130 across the board. 13,000 miles later...I'm doing another one tomorrow.
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Old 11-21-2005, 11:30 PM   #3
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interested as well.

50% leakdown seems off. sure you don't mean 5% leakdown?
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Old 11-22-2005, 12:15 AM   #4
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Quote:
Originally Posted by SloRice
I did a comp. check with 800 miles on my rebuilt motor with CP pistons. I had 130 across the board. 13,000 miles later...I'm doing another one tomorrow.

Cool so 130 sounds about right then..
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Old 11-22-2005, 12:16 AM   #5
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Quote:
Originally Posted by TexRex2002
interested as well.

50% leakdown seems off. sure you don't mean 5% leakdown?

Nah that workshop couldnt believe how high the leakdown was and yes they kept on saying that it was 50%.. This would also correspond with the compression figures that got also..
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Old 11-22-2005, 01:26 AM   #6
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Tino, didn't you get this figured out yet or is this just a second thread?
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Old 11-22-2005, 05:01 AM   #7
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Quote:
Originally Posted by flycaster
Tino, didn't you get this figured out yet or is this just a second thread?
Fly its a second thread went to the orginal engine builder today and we redid the compression test after the car was idling for 10mins...

He thinks that theres nothing at all wrong with the engine...


interestingly he has put a competition cometic head gasket which has lowered the compression to 8:2.5:1.. i wonder if this could have an effect on the top end power curve??
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Old 11-22-2005, 06:19 AM   #8
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Quote:
Originally Posted by tino
Fly its a second thread went to the orginal engine builder today and we redid the compression test after the car was idling for 10mins...

He thinks that theres nothing at all wrong with the engine...


interestingly he has put a competition cometic head gasket which has lowered the compression to 8:2.5:1.. i wonder if this could have an effect on the top end power curve??
Obviously you need to get a definitive independent answer as to the state of the motor. If it is not damaged, I would think that top end loss only is more likely attributable to cams,cam timing or other flow restriction (such as a TMIC).
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Old 11-22-2005, 07:13 PM   #9
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Quote:
Originally Posted by macaws
Obviously you need to get a definitive independent answer as to the state of the motor. If it is not damaged, I would think that top end loss only is more likely attributable to cams,cam timing or other flow restriction (such as a TMIC).

Im goin to get a test done from another worshop to make it 3 in total... i was thinking that its cam timing howver the readout from the M800 ecu suggests that the cams are moving ect correctly.. The heads and cams are from an aussie spec 2.0ltr sti engine...

Ive got a FMIC so there wouldnt be any restrictions from that..
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Old 11-22-2005, 08:02 PM   #10
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i have heard the cam timing argument, but not done the math on how many degrees it is off. I wonder in the timing belt stretches more than a few thousandths, which would according to that theory also wreak havoc on cam timing.

tomorrow if I have a lull at work I will do the math.
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Old 11-22-2005, 09:17 PM   #11
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Quote:
Originally Posted by TexRex2002
i have heard the cam timing argument, but not done the math on how many degrees it is off. I wonder in the timing belt stretches more than a few thousandths, which would according to that theory also wreak havoc on cam timing.

tomorrow if I have a lull at work I will do the math.

That would be great... i wonder however wont an aftermarket engine management show from the cam sensors that the cams are out??
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Old 11-22-2005, 09:50 PM   #12
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make sure you have the throttle body open all the way...i.e. put your foot on the gas!!

Tonight with it closed, I made 120 across the board...scared the ish out of me.

Then did it with it open and made 135 across the board.
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Old 11-23-2005, 05:28 AM   #13
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Quote:
Originally Posted by tino
Im goin to get a test done from another worshop to make it 3 in total... i was thinking that its cam timing howver the readout from the M800 ecu suggests that the cams are moving ect correctly.. The heads and cams are from an aussie spec 2.0ltr sti engine...

Ive got a FMIC so there wouldnt be any restrictions from that..
Exactly what do you call a "loss" of top end power ? This "loss" may be normal for your setup. Consider this-- I have the Aussie spec 2.0L STI. I have run a sz49 and currently run a sr55 (no good reason for the change- its a long story), with FMIC. Power also drops at high revs because quite simply the cams can't flow the highly boosted air.The cams are not as aggressive as the Spec C cams.
Now you are trying to flow much more air with a bigger turbo and extra displacement. I THINK YOU NEED AFTERMARKET CAMS.
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Old 11-23-2005, 06:14 AM   #14
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Quote:
Originally Posted by macaws
Exactly what do you call a "loss" of top end power ? This "loss" may be normal for your setup. Consider this-- I have the Aussie spec 2.0L STI. I have run a sz49 and currently run a sr55 (no good reason for the change- its a long story), with FMIC. Power also drops at high revs because quite simply the cams can't flow the highly boosted air.The cams are not as aggressive as the Spec C cams.
Now you are trying to flow much more air with a bigger turbo and extra displacement. I THINK YOU NEED AFTERMARKET CAMS.

power starts to build at 4500rpm then drops off severly at 5250rpm and its only making around 220kw atw at this level.. In saying that there are ppl over in sydney with the exact same setup heads, cams turbo and head gasket running 320kw atw on 98ron fuel..
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Old 11-25-2005, 01:57 AM   #15
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Quote:
Originally Posted by tino
power starts to build at 4500rpm then drops off severly at 5250rpm and its only making around 220kw atw at this level.. In saying that there are ppl over in sydney with the exact same setup heads, cams turbo and head gasket running 320kw atw on 98ron fuel..
I guess we're back where we started then. You will need to get to a good workshop and go through every possible cause-- boost leaks, compression cam timing, ecu settings etc.
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Old 11-25-2005, 02:16 AM   #16
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Forged pistons require extra clearance due to expansion when the block is honed. If the shop who did the block didn't know you'd bve using forged pistons you might have problem with binding rings. If they honed for one size and you used another, this would explain low compression as well. If the rings didn't seat to begin with, tell the shop that rebuilt it that you want it done correctly.
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