why is my car missing 30rwhp?(compression #'s inside)
01-25-2004, 10:20 PM
#1
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why is my car missing 30rwhp?(compression #'s inside) first let me explain the situation. the car had been feeling slow lately, so I took it and got it dynoed and it only made 348rwhp, 318tq.
setup:
'99 Z28 6spd
Pacesetter LT's, whisper lid, home ported TB, F1 cam w/ comp 918's, Lanes 3" true duals, full LS1 Edit tuning by Chris Robinson
finally got around to doing a compression test today, and was just wondering what all you knowledgable people thought about the numbers. this was on a cold motor, with the throttle held wide open:
1-140
3-145
5-140
7-140
2-140
4-125
6-140
8-140
number 4 is obviously the one that is low, does this look like a headgasket problem? or maybe a bent valve? what do you guys think?
setup:
'99 Z28 6spd
Pacesetter LT's, whisper lid, home ported TB, F1 cam w/ comp 918's, Lanes 3" true duals, full LS1 Edit tuning by Chris Robinson
finally got around to doing a compression test today, and was just wondering what all you knowledgable people thought about the numbers. this was on a cold motor, with the throttle held wide open:
1-140
3-145
5-140
7-140
2-140
4-125
6-140
8-140
number 4 is obviously the one that is low, does this look like a headgasket problem? or maybe a bent valve? what do you guys think?
01-26-2004, 08:09 AM
#4
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Number 4 is 10% out, I would repeat the cranking
compression test just to be sure it wasn't a fluke.
These are pretty high pressures for a cam of any
overlap; 10.5:1 cranking compression is pretty good.
You might try a leakdown test to diagnose the
leakage path (if any); compressed air in the plug hole,
listen for where it comes out. Crankcase=rings,
intake/exhaust = valve or head gasket. Springs by
inspection up top (for any gross tension drop /
breakage).
Bent pushrod hurts opening, not closing, not a
likely culprit here.
compression test just to be sure it wasn't a fluke.
These are pretty high pressures for a cam of any
overlap; 10.5:1 cranking compression is pretty good.
You might try a leakdown test to diagnose the
leakage path (if any); compressed air in the plug hole,
listen for where it comes out. Crankcase=rings,
intake/exhaust = valve or head gasket. Springs by
inspection up top (for any gross tension drop /
breakage).
Bent pushrod hurts opening, not closing, not a
likely culprit here.
01-27-2004, 06:22 PM
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Originally Posted by jimmyblue
Number 4 is 10% out, I would repeat the cranking
compression test just to be sure it wasn't a fluke.
These are pretty high pressures for a cam of any
overlap; 10.5:1 cranking compression is pretty good.
You might try a leakdown test to diagnose the
leakage path (if any); compressed air in the plug hole,
listen for where it comes out. Crankcase=rings,
intake/exhaust = valve or head gasket. Springs by
inspection up top (for any gross tension drop /
breakage).
Bent pushrod hurts opening, not closing, not a
likely culprit here.
compression test just to be sure it wasn't a fluke.
These are pretty high pressures for a cam of any
overlap; 10.5:1 cranking compression is pretty good.
You might try a leakdown test to diagnose the
leakage path (if any); compressed air in the plug hole,
listen for where it comes out. Crankcase=rings,
intake/exhaust = valve or head gasket. Springs by
inspection up top (for any gross tension drop /
breakage).
Bent pushrod hurts opening, not closing, not a
likely culprit here.
thanks