Lost RPM & boost
#15
Registered
We just dynoed my LS setup. and lost 1.8psi from first pull to second pull then held consistent. Had rubber dust behind pulley. Check your belt. Definite pissibility
#16
Registered
Thread Starter
The compressions numbers varied from 85 to 90 PSI per cylinder @ 6500' elevation. Before the blower installation I believe the compression numbers were closer to 110 per cylinder. The blower belt only has about 20hrs on it & no signs of belt dust anywhere. I did get a leak down tester but haven't had time to test yet.
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Itsallgood995 (07-14-2020)
#18
Platinum Member
Platinum Member
110 psi at 6500-7000' elev is around 135psi sea level. That's ballpark for a blower motor that's intentionally built with lowish compression.
90 psi is 110psi sea level which indicates a sick motor. You'll be lucky if it's just head gaskets.
Belt slippage can happen with no obvious signs, but you need to resolve any longblock issues before you go any farther.
I assume both compression readings were done with slightly warm motor and throttle wide open? If not, you could have test variations affecting the readings.
Leakdown. Do a good leakdown. Either have it done by somebody trustworthy or have them there to assist you.
M
90 psi is 110psi sea level which indicates a sick motor. You'll be lucky if it's just head gaskets.
Belt slippage can happen with no obvious signs, but you need to resolve any longblock issues before you go any farther.
I assume both compression readings were done with slightly warm motor and throttle wide open? If not, you could have test variations affecting the readings.
Leakdown. Do a good leakdown. Either have it done by somebody trustworthy or have them there to assist you.
M
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TomZ (06-25-2020)
#19
Registered
Thread Starter
I did the leak down after watching a utube university video. I pulled the plugs, inserted the hose into the cylinder & bumped the starter till I felt the compression build. Then I hooked up the the leak down tester & read the gauge. All the the cylinders were in the high 40's to mid 50% range. You could feel & hear the air coming from the valve cover port. Is this beyond just replacing the head gaskets?
#20
Platinum Member
Platinum Member
iTrader: (2)
Never a fan of the leak-down test. Either it holds or it doesn’t. I do a compression test to look for low cylinders. From there I pressurize that bad ones to hear where leaks are coming from... intake or exhaust... head/valves. Coming from the crankcase (valve covers) rings or a hole in a piston.
In your case ... sounds like the lower-end is tired sir. Rings or holed piston(s).
Wish it was better news.
In your case ... sounds like the lower-end is tired sir. Rings or holed piston(s).
Wish it was better news.
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Unlimited jd (07-13-2020)