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1994-1995 5.0 Mustang SN95 Tech Forum

5.0L Talk | 5.0L Tech | 94-95 Tech | 1979-1993   1994   1995   Upload Pictures | Timeslips | Power Adders | Mustang Tech 


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Unread 10-10-2005   #1 (permalink)
Aslan45 is offline Rookie


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Default Stock 95 5.0 Compression Pressure??

Going to run compression check on my 5.0 w/90k miles. Books talk about all cylinder pressure readings being within 15-25% of each other as good. I want to know what the original pressure was in psi for a better assessment of contition because if all cylinders are 50-63 psi they are within 25% of each other so are good according to Chilton's compression check procedure. I think I read the pressure should be 135 psi but can't remember where or if these are even the right values. Will one of you tech spec guys out there help me, give me a number, give me a source document? Thanks in advance.
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Previous stangs: 66 GT, 65, 67.
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Unread 10-10-2005   #2 (permalink)
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I believe a good cyl pressure to be between 110-130 ish. so 60 sounds really low to me, we just rebuilt my 95 5.0 for the second time. (harmonic balancer flew off and killed all the new bearings ) and we checked them at 110-120.....
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Unread 10-11-2005   #3 (permalink)
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Quote:
Originally Posted by Aslan45
Going to run compression check on my 5.0 w/90k miles. Books talk about all cylinder pressure readings being within 15-25% of each other as good. I want to know what the original pressure was in psi for a better assessment of contition because if all cylinders are 50-63 psi they are within 25% of each other so are good according to Chilton's compression check procedure. I think I read the pressure should be 135 psi but can't remember where or if these are even the right values. Will one of you tech spec guys out there help me, give me a number, give me a source document? Thanks in advance.
The compression specification I have from a Motor Engine Repair manual I think is too broad, it specifies a "good" figure to be anything from 110 psi to 215 psi and a 25% variance factor.
Based on my experience, I use a "working" compression figure of 105 psi, anything less will cause a miss, intermittent or fixed @idle. I keep a 20% factor to determine if there are any problems (valvetrain, timing, head gasket failures, etc) with the engine but, anything below 105 psi needs attention.
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Unread 10-13-2005   #4 (permalink)
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Thanks mrbob and Joel. Good info. However mrbob you misunderstood my 50-63 psi example. I haven't measured yet. The example was just to illuminate the misleading spec in Chilton's that a 25% variation between cylinders is acceptable without giving an actual pressure reading as a baseline. With 88k pretty easy miles on the motor, I'm hoping my pressure is still in the 110-120 psi range.

Thanks again, guys.
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95 GT vert: HPM Mega-bite Jr's & subframes, Eibach Pro Kit, Magnaflow catback & O/R X-Pipe, MAC equal shorties and CAI w/K&N, Pro5.0, King Cobra Clutch, Strange Engineering shocks/struts, ported TFS TW heads, TFS 1.7 roller rockers, Explorer intake, FRPP 65mm TB, Maximum Motorsport tower brace.

Previous stangs: 66 GT, 65, 67.
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