Hey guys, I need some help with compression.  Can anyone tell me what the compression levels should be on a 75 440 and a 72 400.  My 440 is averaging 129 and my 400 averages 105.  Also how do you calculate what your overall engine compression ratio is?  Thanks in advance for your help.  

The 440 has very good compression for a 75 motor.
Calculating your average compression ratio takes a lot of math so instead of going that route I will give you a general rule of thumb for stock engines.
1. 150 lbs. compression = 10.5/1 compression ratio.
2. 100 lbs. compression = 7.5/1 compression ratio.
If your vehicle is equipped with a larger than stock cam your compression numbers will read about 10-25% lower due to overlap and Duration of the cam.  
Another general rule of thumb is the weakest cyl. should be no less than 10% lower than the highest cylinder.
lets say cyl. 1 on the 400 reads 100 lbs.
    cyl 8 reads 110 lbs. Acceptable, however 105 lb average for the 400 is on the low side to begin with. 70's mopar engines were known to develop a build up of carbon around the valves. You can correct this by decarbonizing the engine, pour a can of carb cleaner down the throat of the carberator. This needs to be done in a well ventelated area, with the tailpipe facing down wind in a non populated area.
With the engine running slowly poor about half a can of carb cleaner down the carb, with your other hand operate the throttle so the engine won't stall.
Once you have installed half the can of cleaner dump the rest of the can into the carb and let the engine stall.
Let the vehicle sit for 20-30 minutes. You are letting the cleaner losen any carbon around the valves.
After that you need to start the engine and take it for a good drive on the highway. Start the engine by holding the gas pedal on the floor until the engine starts, do not let it stall. Drive it to your favorite place were there are not a lot of people. The vehicle will beltch out smoke for the first 2-3 minutes, after a 15-20 minute drive on the highway bring it back, change the oil to a 10/40, and recheck the compression numbers, chances are they will be up 10-20% and the engine will feel like it has been reborn.  
If you are not comfortable doing this job, you can have it done at a local service centre for probably less than an hrs. labour.  

Thank you very much.  I appreciate you taking the time to help me out and type this out.  I'll give it a go this weekend.