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Author Topic: engine compression specs  (Read 1279 times)

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Chazza12

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engine compression specs
« on: 26 January 2018, 22:17:30 »

does anyone know the compression specs on 20.16v engine is ? thanks going to check them and see what they are but need a base line to go from. thanks
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Nick W

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Re: engine compression specs
« Reply #1 on: 26 January 2018, 22:54:10 »

I wouldn't worry too much about the actual numbers unless you have an accurately calibrated gauge. Good technique, which includes cranking for the same amount of time and with the throttle open, is more important. What you're actually looking for is that all the cylinders give similar readings.


A leak-down test is more useful, but does require more expensive equipment.
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Chazza12

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Re: engine compression specs
« Reply #2 on: 27 January 2018, 06:19:24 »

i have a brand new gauge, needs testing to calibrate. says test the calibration with known pressure, so thought engine compression test, if its out too much need to send it back for replacement, old one had lasted 30 year but its way out.  suppose could test it on tyre pressure, just need to know if the pressure is right ? best of 3 gauges ? have 3 digitals. might work..
   
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TheBoy

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Re: engine compression specs
« Reply #3 on: 27 January 2018, 09:35:56 »

I'm with Nick W on this.

The 2.0l is not prone to wear, except cylinder 1, so looking for all 4 to be similar.
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Bigron

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Re: engine compression specs
« Reply #4 on: 27 January 2018, 10:08:16 »

I think the OP wants an absolute pressure rather than a relative one, to calibrate his instrument, yes? In which case, he is seeking a known and accurate pressure source for calibration/verification. Where on earth would you find one of those, cheaply? I bet the NPL would want a bucketload of money!

Ron.
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Chazza12

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Re: engine compression specs
« Reply #5 on: 27 January 2018, 17:33:12 »

i will have the bucket load of money lol. thanks TB so cylinders 2 to 4 would be a good reference :y.
as this is all can find
The breakdown of the engine name [2] is as follows:
X - Exhaust emissions level: 94/12/EC, stage 2
20 - 2.0 L
X - Compression ratio - 10.011.5:1
E - Mixture system - Injection
V - Specific version - Volume Model
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Bigron

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Re: engine compression specs
« Reply #6 on: 27 January 2018, 17:59:33 »

Then take your money-bucket and your pressure guage to here:-
https://en.wikipedia.org/wiki/National_Physical_Laboratory_(United_Kingdom)

Ron.
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Nick W

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Re: engine compression specs
« Reply #7 on: 27 January 2018, 18:03:31 »

I think the OP wants an absolute pressure rather than a relative one, to calibrate his instrument, yes? In which case, he is seeking a known and accurate pressure source for calibration/verification. Where on earth would you find one of those, cheaply? I bet the NPL would want a bucketload of money!

Ron.


This is why we're suggesting he actually use the gauge he has, and goes from there. I'm not even sure if the cheapy gauge I have is even marked in units, just various marks.
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LC0112G

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Re: engine compression specs
« Reply #8 on: 27 January 2018, 20:03:14 »

The equation for converting compression ratio into pressures is :

 P = Po * (CR ^ g) where

P = corrected cylinder pressure
Po = Initial cylinder pressure (at BDC) = 1 Bar Atmospheric (14.7 psi) at low RPM and with no boost
CR = Compression ratio
g (gamma) = specific heat ratio of the gas - somewhere between 1.2 and 1.4 for fuel+air.

However, The problem with a car engine is that the inlet valves don't close till after BDC - It's determined by the camshafts and typically somewhere around 50-60 degrees after BDC. This means the real compression ratio (the Dynamic Compression ratio) will be less than the book figure because the piston is already some way up the bore before the inlet valve slams shut. This is particularly true at low RPM, such as when cranking. Whilst the swept volume of the engine may be 1998cc, the swept volume of each cylinder when the valve finally shuts won't be 500cc. Therefore without knowing what the cam profile is, you can't use the above equation to calculate a reliable pressure (in PSi).
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Chazza12

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Re: engine compression specs
« Reply #9 on: 28 January 2018, 10:42:55 »

just had message back from vauxhall/ well opel germany and they say minuum is 110 psi and max 30% highest and lowest  engine cold. other test is running engine for 10 minutes, then test again 115 to 120 psi  lowest. still max plus 30%. or cold test with 3 drops of oil in each cylinder. no more than 3 drops. so going to see what it says if it's not raining. missed a bit out max 10% drop between cylinder any more than 10% then there is a problem.
« Last Edit: 28 January 2018, 10:56:51 by Chazza12 »
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LC0112G

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Re: engine compression specs
« Reply #10 on: 28 January 2018, 20:50:36 »

just had message back from vauxhall/ well opel germany and they say minuum is 110 psi and max 30% highest and lowest  engine cold. other test is running engine for 10 minutes, then test again 115 to 120 psi  lowest. still max plus 30%. or cold test with 3 drops of oil in each cylinder. no more than 3 drops. so going to see what it says if it's not raining. missed a bit out max 10% drop between cylinder any more than 10% then there is a problem.

Sorry, but 110/115/120 psi is waaaayyyy too low. That's only about 7.6 bar. If the compression ratio letter is "X = 10.0-11.5" then it's going to be more like 200psi/14 bar.
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Chazza12

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Re: engine compression specs
« Reply #11 on: 29 January 2018, 12:52:19 »

well went ahead and done the test.
                   
                 Dry
piston.
         No.1 180 psi
         N0.2 185 psi
         no.3 180 psi
         no.4 180 psi
               
                wet 3 drops oil

         no.1 185 psi
         no.2 185 psi
         no.3 190 psi
         no.4 180 psi
so i'm now thinking it might be leaking on the valves a bit would this be the case or does it look about right ?
as oil will seal the piston rings, so inlet and exhaust might be leaking a bit ????
would that sound about right ???

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Nick W

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Re: engine compression specs
« Reply #12 on: 29 January 2018, 13:04:44 »

Nothing wrong there.
What's the fault you're trying to find?
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Chazza12

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Re: engine compression specs
« Reply #13 on: 29 January 2018, 13:51:01 »

 i do get engine rock. and sometimes it dont like to go up a hill have to drop down an gear sometimes 2, just started engine up and idle has gone up so think will have to leave it till the oil has dropped down, past the rings, over night should be fine. but main problem was starting engine run up road for 5-6 miles and its gray white smoke,, but had engine head test done and no leaks on that and now water lose. could it be the fuel ????
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LC0112G

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Re: engine compression specs
« Reply #14 on: 29 January 2018, 14:51:47 »

well went ahead and done the test.
                   
                 Dry
piston.
         No.1 180 psi
         N0.2 185 psi
         no.3 180 psi
         no.4 180 psi
               
                wet 3 drops oil

         no.1 185 psi
         no.2 185 psi
         no.3 190 psi
         no.4 180 psi
so i'm now thinking it might be leaking on the valves a bit would this be the case or does it look about right ?
as oil will seal the piston rings, so inlet and exhaust might be leaking a bit ????
would that sound about right ???

I rebuilt my C36GET engine last year. Book compression ration is 8.2:1. Measured wet pressures on all 6 were 12 bar (176 psi) +/- perhaps 0.5 bar.

So my take is that all these figures are on the low side for a 10:1 compression ratio - but I don't know anything about the X20XE engine, and I have no calibration data for my pressure gauge, and you have no calibration for yours So lots of unknowns.

The fact that in your results they're all very close says there isn't anything dramatically wrong with any particular cylinder. Doubt it's valve related. It could be overfueling, but you'd expect the lambda sensors to be complaining big time if it were that. How many miles on the engine? If it's a high miler could also be worn rings and/or bores. 
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