100 PSI compression test results

1. BlackBox L-plater Joined: Apr 2009 Hitchin Posts: 49 106 GTI 140BHP

   #1 21st July 2012, 19:07

   100 PSI on all 4 cylinders dry
   
   115 - 125 PSI on cylinders when wet
   
   I heard cammed engines get lower compression?
   
   Or is my engine just buggered?
2. user_57064 Established Member Joined: Jan 2012 south essex!! Posts: 2442 posi blue vtrs race car

   #2 21st July 2012, 19:29

   Quote:

   Originally Posted by BlackBox 100 PSI on all 4 cylinders dry 115 - 125 PSI on cylinders when wet I heard cammed engines get lower compression? Or is my engine just buggered?

   Is that on all cylinders? Thats low... Even for a cammed engine... Wouldnt say anything wrong just worn if its on all cylinders
   
   Sent from my GT-I9100 using Tapatalk 2
3. BlackBox L-plater Joined: Apr 2009 Hitchin Posts: 49 106 GTI 140BHP

   #3 21st July 2012, 21:25

   Quote:

   Originally Posted by greyjasper51 Is that on all cylinders? Thats low... Even for a cammed engine... Wouldnt say anything wrong just worn if its on all cylinders Sent from my GT-I9100 using Tapatalk 2

   Yeee booii all 4 cylinders. Was hoping someone with cams would post their results.
4. welshpug Saxperience Forum Bum Joined: Jul 2010 South Wales Posts: 3078 ZX 16v, 205 GTI, 309 Goodwood, 405 MI16.

   #4 21st July 2012, 22:47

   throttle closed?
5. Quick Saxperience Post Whore Joined: Mar 2003 United Kingdom (England) Posts: 7064

   #5 21st July 2012, 22:48

   Try adding a drop of oil, then repeating!
6. f13sta Established Member Joined: Sep 2010 loughborough Posts: 2229 1988 ford fiesta mk2 1.4- 2001 black saxo furio (d

   #6 21st July 2012, 23:17

   Quote:

   Originally Posted by Quick Try adding a drop of oil, then repeating!

   Quote:

   Originally Posted by BlackBox 100 PSI on all 4 cylinders dry 115 - 125 PSI on cylinders when wet

   
   
   does sound very low mate. have you had a headgasket done at all? does it missfire.
   just to put inperspective the highest DRY compression i recently have on my 1.4 8v was 200psi lowest was 175 psi, and did the h/g last summer.
   
   can't see why a cammed car would have lower compression, as far as i'm aware the cam profiles just mean the valves stay open longer to standard. did you do the compression test on a warm engine?
7. user_39461 Super Moderator Joined: Nov 2009 Cambridge(ish), UK. Posts: 10581 BMW 5x M50d.

   #7 22nd July 2012, 00:19

   As above - throttle open or closed?
8. BlackBox L-plater Joined: Apr 2009 Hitchin Posts: 49 106 GTI 140BHP

   #8 22nd July 2012, 00:49

   Quote:

   Originally Posted by welshpug throttle closed?

   Quote:

   Originally Posted by RossDagley As above - throttle open or closed?

   
   
   This is with throttle open
   
   I got 75 PSI without throttle
   
   
   
   

   Quote:

   Originally Posted by Quick Try adding a drop of oil, then repeating!

   
   
   115 - 125 PSI is the result I got with oil
9. BlackBox L-plater Joined: Apr 2009 Hitchin Posts: 49 106 GTI 140BHP

   #9 22nd July 2012, 00:53

   Quote:

   Originally Posted by f13sta does sound very low mate. have you had a headgasket done at all? does it missfire. just to put inperspective the highest DRY compression i recently have on my 1.4 8v was 200psi lowest was 175 psi, and did the h/g last summer. can't see why a cammed car would have lower compression, as far as i'm aware the cam profiles just mean the valves stay open longer to standard. did you do the compression test on a warm engine?

   No headgasket done recently. Car doesn't missfire, the only problem i've had is it dumps lots of oil at high revs through the oil breather. Engine was still warm, tested about an hour after some driving.
10. user_39461 Super Moderator Joined: Nov 2009 Cambridge(ish), UK. Posts: 10581 BMW 5x M50d.

    #10 22nd July 2012, 00:55

    Quote:

    Originally Posted by BlackBox No headgasket done recently. Car doesn't missfire, the only problem i've had is it dumps lots of oil at high revs through the oil breather. Engine was still warm, tested about an hour after some driving.

    Rings. Pressurising crankcase.

    1 user thanked this post: BlackBox
11. BlackBox L-plater Joined: Apr 2009 Hitchin Posts: 49 106 GTI 140BHP

    #11 22nd July 2012, 00:58

    Quote:

    Originally Posted by RossDagley Rings. Pressurising crankcase.

    Damn...
12. user_39461 Super Moderator Joined: Nov 2009 Cambridge(ish), UK. Posts: 10581 BMW 5x M50d.

    #12 22nd July 2012, 20:22

    sorry buddy. Most likely though, especially with the heavy breathing at high revs (as you're driving gasses down the bores).
13. Gordzilla Established Member Joined: Mar 2007 Edinburgh Posts: 2369

    #13 22nd July 2012, 20:36

    What should the PSI figures be on a healthy engine ? 100psi is low. I've recently had to do engine work on another car that had low compression and it was piston failure. Needed an engine rebuild.
14. user_39461 Super Moderator Joined: Nov 2009 Cambridge(ish), UK. Posts: 10581 BMW 5x M50d.

    #14 22nd July 2012, 21:11

    Ideal results should be 20 times compression ratio (in psi). Engine should make that pressure by 6th turn of the engine, with 80% by the 4th turn, and around 66% by the 2nd turn.
    
    You want (again ideally) no more than 14psi difference across the 4.
    
    if the engine takes longer to build compression (IE 10 revolutions to reach max pressure) look at rings - a wet test will confirm.
15. blackie_2k5 Saxperience Hardcore! Joined: Oct 2008 Birtley Posts: 22253 VTR Turbo, 106 xsi track slag, Transit recovery, B

    #15 22nd July 2012, 21:18

    Anything under 10 bar is considered low
    
    So anything under 150psi really