Programming is a big part of that, yeah. On ours, I think we have empirical evidence from a member that it does. (at least, a bad one does.) That's the idea behind the non-fouler trick. Makes the PCM think the cat is there, and doing it's job properly.

You are also correct in that having NO exhaust would make our trucks run WORSE. (not to mention burning valves. ) Scavenging is what it's all about. There have been several folks that talked about perceived loss of low end after gutting the cat. I would REALLY like to see some dyno runs done with a cat, with a gutted cat, and an exhaust where the cat was replaced with a piece of pipe. (like the jegs off-road pipe for instance.) That would be really enlightening.

 

I have 3.42 gears with 285/75/16 tires. Would that contribute to poor milage?

 

3.55 gears are stock.... I've never heard of 3.42...but if the tires are larger than stock it wont help with stock gears... one size bigger doesnt have much of an effect...

 

I can't say that I have seen a huge difference in gas mileage over the last couple of days since I gutted my cat but haven't really drove it that much. I have noticed quite a bit of power difference. Doesn't seem like it takes quite as much throttle to get up and go. But my cat was partially clogged so I'm sure a gutted cat is better than a partially clogged cat. I will probably end up replacing the cat down the road when I get a better exhaust system. I'm getting a new muffler today but just taking the cheap route for right now(too many other projects at the moment) and leaving the gutted cat in. Will see how it does and then go from there. Also will probably pick up some non-foulers while I'm out to get rid of my CEL.

 

Probably 3.55s.... but, with 33" tires.... yeah, that's a definite contributor.

 

They are 3.42s i took off the pan and checked

 

Then someone changed them in the past, as dodge never put that ratio in the trucks.