[QUOTE=65x2]I have an 80 gal 5hp unit from Northern and it runs almost constantly when I use my mud hog to cut filler; I'm about to pipe it into my 60 gal unit that went bad. So I'd definitely say bigger is better. Like stated especially if you plan to paint./QUOTE]
If you are disappointed with that thing now just wait (and you will be doing a LOT of that!) until you are trying to recharge a 140 gal tank! As has been said over and over and over and over, "A BIG TANK DOES NOT MAKE A BIG COMPRESSOR"!!!
Sure you will get a little more run time at first, but a lot less than you may be thinking and then comes the trade off, you will be in for a looooong wait for the compressor to recover when it runs out of air which it will still do. Your problem is the pump is not replacing the air as fast as it is being used and more tank capacity will not help this. Running out of air with a sander when trying to use a tank that big would be a PITA but at least you could take a break while the compressor is recharging (and most likely overheating also due to the prolonged run time) but running out while spraying paint could be a disaster! If you are using a HVLP gun for instance and your pressure runs low you will most likely exceed the flash times while waiting for that thing to recover. Your pump is already too small for the tank you have which is common on these econo compressors and adding even more tank capacity is going to make things worse not better, here's one big reason why- A bigger tank may run a bit longer before running out of air but then it takes a correspondingly longer time to recharge so the run time vs the wait time is the same and you gain nothing! Those long recharge times will cause the pump to get hot and a hot pump/air causes a loss of efficiency which means your pump will produce less air the hotter it gets. By exceeding the duty cycle and allowing the pump to run hot that big tank will actually make your compressor less efficient causing you to have to wait even more than you would with the smaller tank. Bigger is better? Actually what you have is an example of what I mentioned earlier about some 80 gal models that would work better with a 60 gal tank, bigger is NOT better in this case!