my whole passenger bank on my 88 305 is 15psi low on the compression check.
What are your thoughts???
bhg? theirs no oil in the water.
the machine shop screwed up one whole side of valves the same? no way.
it doesnt smoke white smoke, it does black because it burns pig rich.
should i re torque head?

 

What was done to the engine, just a valve job? How many miles on the engine overall? A compression test measures how much pressure a cylinder can build and/or hold. The lower it is, the more you are losing through worn rings or valves. It's weird that your whole right bank is off by the same amount though. If you have an oil can (squirter), you can shoot oil inside each cylinder, trying to aim around to coat the circumference of the cylinder wall. Give another test, and if your numbers jump, it's your rings that are causing the lower numbers. What was your highest reading? Normally, in the neighborhood of a 10% difference between your highest and lowest is considered acceptable.

 

You may want to do a leak down test.

 

maybe 3k on the motor full rebuild, rebuild 1yr ago and has never run right due to computer but thats another subject that yall already trouble shot with me.
high comp pistons aftermarket cam.
compression was fine after rebuild all the way up to 2k on motor. we haven't changed anything since.

i have to find comp. readings. i think good bank was 190 and bad bank was 175-178
leak down test. the compression held for 10sec after and then i pulled it off.
thanks for the reply's

just so you know we did the compression test just to be sure the motor was good so we could buy the custom chip it needs.

 

I would redo the compression test with adding a teaspoon of oil to each cylinder. 175PSI is still a good number, but it should not vary that much from one side of the engine to another.

A leak down test is the correct way to find where you're losing compression however.

 

i will redo the test with some oil.
175 is maybe good for stock but i have higher compression pistions.

 

what type of fuel injection is it? you say its running rich. if one bank is richer than the other, which is very easy on the tpi or tbi setups (as well as carb), one side could be washed down with more fuel, reducing the oil on cylinder walls thus creating blow buy. perform a leak down test and listen for air in the breather or dip stick tube.