Author Topic: Compression / Leakdown results from Vex  (Read 2437 times)

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Offline tcon

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Compression / Leakdown results from Vex
« on: November 11, 2015, 02:29:59 PM »
So I brought my 2012 STI into Vex today for a compression / leakdown test, I was a little curious about some seemingly excess oil consumption, and I want to be prepared before I start modding it for more power. The results were as follows;

#1 - 120psi - 3%
#2 - 120psi - 3%
#3 - 120psi - 3%
#4 - 120psi - 6%

The leakdown results obviously seem within spec, and it's my understanding that cylinder 4 is always the worst, so no problems there right? Well I'm a little confused about the compression. I thought it should be up around 140psi shouldn't it? Would there be any reason for them to just take it up to 120 and stop? I know the car sat outside for maybe 30-45 mins before they actually started, but I don't know what the range would be like between hot and cold engines... I would have inquired about this while I was there but I didn't really look into what the results should be until I got home. Has anyone else had this done at Vex, and maybe able to offer some input here? Thanks.

Offline Zac

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Re: Compression / Leakdown results from Vex
« Reply #1 on: November 11, 2015, 03:15:47 PM »
I think the biggest concern people are looking for is huge variances between cylinders.

Offline Jay89

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Re: Compression / Leakdown results from Vex
« Reply #2 on: November 11, 2015, 03:40:57 PM »
You generally want to do compression tests hot.

Don't worry so much about the numbers. As long as it's pretty much over 110 you're fine. All 4 seem to be very very close. (I'm assuming it's not exactly 120 across the board but its near enough to make no big difference) that's pretty much perfect.

I wouldn't worry about a thing.

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Offline mudferret

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Re: Compression / Leakdown results from Vex
« Reply #3 on: November 21, 2015, 10:14:30 AM »
We see lower compression numbers here as well because of elevation.

Offline RockThePylon

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Re: Compression / Leakdown results from Vex
« Reply #4 on: November 21, 2015, 11:35:26 AM »
We see lower compression numbers here as well because of elevation.

This is also true. Around 10% lower at Calgary's altitude.
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Offline krisr33

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Offline Dynamic Entry

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Re: Compression / Leakdown results from Vex
« Reply #6 on: August 30, 2016, 06:43:20 PM »
I just did a compression test on the JDM ej205 in my WRX with the engine cold

1 - 151psi
2 - 147psi
3 - 151psi
4 - 148psi

Does the altitude loss (~9% @ ~3000 feet in Calgary) indicate that my cylinders would be making ~164psi at sea level when cold

I know that we should look more closely at variance than raw score, because different guages will provide different results.

But still, those numbers are drastically higher than the 120psi on the STi mentioned above.

Maybe the motors have different compression ratios.
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Offline toytech

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Re: Compression / Leakdown results from Vex
« Reply #7 on: August 30, 2016, 09:45:54 PM »
Nice and even is what you want to see , all sorts of things play into compression numbers newer engines with variable valve timing are going to baseline the cams at some position with some kind of overlap that can cause higher/lower numbers than older cars , dont worry about it . That was a dry test too , if you put some oil in the cylinders the numbers would go up as well but again dosent matter those are good numbers . If it was 90psi across the board then id be worried .

Offline RWDragoon

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Re: Compression / Leakdown results from Vex
« Reply #8 on: August 31, 2016, 11:08:55 AM »
These numbers are considered 100% normal, with our gauge at our altitude.  The leakdown numbers tell us more about the engine than the compression test numbers and in your situation everything looks excellent! 

On cylinder #4 those results are nothing to worry about.  A small piece of carbon holding a valve open just the tiniest amount can cause a slightly lower leak-down test, and you could find doing the test after a drive can change the numbers 1-3% pretty easily. 
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