What should the psi range be? I rented an OEM tools compression kit from Autozone and I'm getting right at 60psi on the cylinders I've tested so far....that seems way to low, but the car starts and runs well, so I'm wondering if the kit is messed up somehow...it holds the pressure as long as I let it sit so doesn't seem to be just a loose connection/silly mistake.
I've unplugged distributer and fuel line, and am cranking for 5-10 seconds
60 psi would be awfully low. Are all the plugs out and the choke and throttle completely open while cranking the motor? I would think that 125 - 185 psi would be more to the norm depending on the condition of the engine.
I'm only doing one plug at a time to keep plug wires straight.. Do I need to take them all out at once?
Hmmm...so choke and throttle need to be open? What would be the best way to facilitate that with the carburetor?
Benjamin,
Pull all the plugs, disconnect the hot wire to the HEI, and manually open the carburetor fully by pulling the cable back. With the secondary throttles open wide, take a long screwdriver and gently insert it into one of the secondary barrels.
Now taking one cylinder at a time, turn the motor over with a fully charged battery for a full 5 seconds. Keep track of the cylinders by number and by readings.
Greg Surfas
Very helpful on procedure- thanks, Greg!
'75 is back in the lower compression era. The spec is 8.5:1 compression ratio.
So 8.5 * 14.7 = 125 in the bottom of the range. Compressing gases/vapors increases temperature so it gets higher in the cylinder. More important that they are pretty even than the absolute value.
There's a follow up "wet" test that you should also do, if low.
Easy to search the procedure.
You'll still have to determine what's wrong if one or more is low. ring, valve, crack, gasket, etc.
colored electrical tape is useful for keeping tabs of which is which.
You can get a set with a few different colors for about $5
If you have some masking tape, just loop a 2" piece over each wire, putting the two sticky sides together to make a writing surface, and write the cylinder number on it. Cheap, and easy to remove when done.
Daryl Chesterman