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ecky7 Astra Enthusiast
Joined: 28 Jul 2010 Posts: 218
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Posted: Mon Sep 06, 2010 9:20 am Post subject: what is a ok compression test reading |
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Hi. what is a ok reading for testing the head. cant find it in the h manual. thanks all.
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matt Moderator
Joined: 30 May 2005 Posts: 5212
Location: West Brom
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Posted: Mon Sep 06, 2010 10:40 am Post subject: |
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Not sure what the exact reading should be but for all engine all four cylinder must be about the same give or take a couple of units
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jo4nny8 Astra Veteran
Joined: 27 Sep 2005 Posts: 1495
Location: Ilkeston, Derbyshire
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Posted: Mon Sep 06, 2010 12:29 pm Post subject: |
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what engine??
as above but if im right in thinking a turbo/low comp engine would be low numbers and normally high, but they should all be the same give or take.
my 1.3 showed compression of approx 150psi across all four cylinders if thats any help
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ecky7 Astra Enthusiast
Joined: 28 Jul 2010 Posts: 218
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Posted: Mon Sep 06, 2010 9:34 pm Post subject: |
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cheers jo4nny. yea it 1.8. couldnt find any info in the manual, unless i missed it.
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Jon_Kadett Astra Legend
Joined: 29 May 2005 Posts: 4087
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Posted: Mon Sep 06, 2010 9:35 pm Post subject: |
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info about the 1.8 is near the back of the haynes
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rip Astra Craftsman
Joined: 12 Feb 2009 Posts: 96
Location: Milton Keynes
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Posted: Tue Sep 07, 2010 7:20 pm Post subject: |
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JON_SR wrote: | info about the 1.8 is near the back of the haynes |
I can't find any values for compression pressures in there though, not for any engine.
Time for some good old maths:
Compression ratio of a 1.3 is 9.2:1 so compressed, should be 10.2 bar. 1 bar = 14.7psi so 10.2*14.7= 149.94, so just about 150psi which is exactly as per Johnny's test.
CR of 1.8 = 9.5:1 so 10.5*14.7= 154.35
So you're looking for around 154. If you have a problem, I would expect this to be well low, like below 120. Also, I doubt all 4 would go at once, so I would be concerned if 1 cylinder was significantly lower than the rest.
Try it several times too. It may not be easy to get a good seal with your compression tester which is why results may vary a little.
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GT/Estate Astra Expert
Joined: 30 May 2005 Posts: 2230
Location: Rotherham
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Posted: Wed Sep 08, 2010 8:17 am Post subject: |
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compression ratio's do not relate to a compression test!
when researching for compression ratio's befor i turbo'd it, it can be all over the place,
see below
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rip Astra Craftsman
Joined: 12 Feb 2009 Posts: 96
Location: Milton Keynes
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Posted: Wed Sep 08, 2010 10:40 am Post subject: |
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GTEstate wrote: | compression ratio's do not relate to a compression test!
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It was only meant as a rough guide. The dynamics of compressing a gas quickly is quite complex & nobody had come forward with a compression chart.
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GT/Estate Astra Expert
Joined: 30 May 2005 Posts: 2230
Location: Rotherham
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Posted: Wed Sep 08, 2010 1:39 pm Post subject: |
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Sorry mate the first bit came across a bit wrong lol, 150psi should be fine as I'm running 7bar 108psi which from the head I'm using is about 7:1 so 150psi should be well into 9:1 most gauges have green n red areas for a rough guide
_________________ 1983 5dr project 1.4Ti in china blue
1983 SR in mat black rat on the road again
1980 5dr Opel estate (9 year ongoing project) |
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astradrew1988 Astra Dabbler
Joined: 04 Nov 2016 Posts: 25
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Posted: Sat Feb 04, 2017 3:18 pm Post subject: |
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Old post I know but I'm just doing this test I only got 7.1 bar across all 4 engine was warm but didn't give it any throttle cranked about 4-5 times is this a low reading and what could it be?
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