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Old 01-14-2013, 02:17 PM   #1
magman007
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Default Compression Test Results?

Hi guys, I'm getting ready to buy an 06 sti and had the owner take the car in for a ppi, compression and leak down test. The dealer was unable to do the leak down due to not having a proper tool? But my real question is with the results.

Cyl 1 was 115 and 2-4 were all 110. I understand that "spec" is between 140 and 170. I have spoken to a tech independent from the situation and they say its not the number but the consistency between the cylinders that matters. The car has 45 k miles on it, was stage 2 AP then pro tuned for the last 2 years and has been returned to stock. The tech that performed the test says he has seen plenty of "healthy" STIs in the 115 120 range.

Now I'm not the smartest or most mechanically inclined but I do understand that compression has a direct correlation to power generation if the compression was 30psi less than spec wouldn't the car be down on power? Am I buying myself a rebuild shortly down the road or should I feel confident in buying an otherwise clean car?

The engine was not "Cold" it still had some heat in it, but was definitely not at operating temp. I have yet to speak to the tech (calling tomorrow) The owner has been nothing short of awesome and great to work with, and I have tickets to go get the car next Saturday. So Nasioc I need to make a decision and i need some assistance.
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Old 01-16-2013, 12:25 AM   #2
BrendanTheGreat408
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First off i am not a subie expert by any means, from my knowledge 110 doesn't sound too healthy. Down on compression can and probably will mean down on power as well and possibly a weak engine. Here are the results from my compression test, the engine is "very healthy"

http://farm9.staticflickr.com/8343/8...fb5a1ebd_b.jpg
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Old 01-16-2013, 01:10 AM   #3
mod maniac
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Location: mariposa ca.
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2002 FOZ STI 2.34
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I don't know if my snap-on gauge reads low but i usually see around 120 on most of the wrx's I test. I would say the numbers look close there probably isn't a problem. There gauge probably just reads low like mine.
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Old 01-16-2013, 03:59 AM   #4
esteve
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I wouldn't buy a used turbo Subaru, especially one that's been modded, without a leakdown test too. Compression tests don't always tell the whole story so try to have the owner take it to a shop that can do a leakdown test.
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Old 01-16-2013, 10:45 AM   #5
myblusti
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it depends on how he performed the test and the tester on the readings. to get the best results you want to get the car to op temp then remove all plugs and the fuel pump fuse then perform the test at wot for about 5 revolutions. if it isnt done at wide open throttle on a warm engine the results will vary, but you do want a consistant number across all cylinders.
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Old 01-16-2013, 01:28 PM   #6
aboothman
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Quote:
Originally Posted by myblusti View Post
it depends on how he performed the test and the tester on the readings. to get the best results you want to get the car to op temp then remove all plugs and the fuel pump fuse then perform the test at wot for about 5 revolutions. if it isnt done at wide open throttle on a warm engine the results will vary, but you do want a consistant number across all cylinders.
agreed
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Old 01-16-2013, 03:14 PM   #7
danger1138
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Quote:
Originally Posted by myblusti View Post
it depends on how he performed the test and the tester on the readings. to get the best results you want to get the car to op temp then remove all plugs and the fuel pump fuse then perform the test at wot for about 5 revolutions. if it isnt done at wide open throttle on a warm engine the results will vary, but you do want a consistant number across all cylinders.
Thats that little 15amp fuse behind the change bin?
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Old 01-17-2013, 08:18 AM   #8
myblusti
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lol. it should say fuel pump. im not sure in your car. in my 240 it is a 15amp. but my sti is at the shop so i cant check. but it should be labeled. you could also probably just unplug the injectors but thats kind of a pita on subaru's.
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Old 01-17-2013, 09:45 AM   #9
AkumaMotorsports
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2008

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I would definitely recommend bringing the car to a place that can do a proper leak down test. The results of this would help you get a better understanding if that reading is accurate and if so why it is down on compression.

By doing the leak down test it will give you more specific reason as to why there is low compression. It will indicate things such as blown head gasket, bad intake or exhaust valves, worn out or damaged piston rings from over heating, constant abuse etc..

Right now there is not enough information to see whats going on.
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Old 01-20-2013, 10:35 PM   #10
jaboyd
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Location: Knoxville, TN
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2011 STI
WR Blue

Default cyl pressure

STIs should be around 140 psi (cold reading) and ideally with no more than a 10-15 psi spread across all cylinders. Mine read 135 on 2 cyls and 140 on 2 cyls avg 137.5.
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Old 01-21-2013, 02:14 PM   #11
revD
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Default

Mine read ~125 cold cranking when I was investigating some things on my last motor. Ran great at the time, but this is also cold.
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