Alright, I have the above truck, 178k miles, with the rear cat gone and single 2.5" pipe w/turbo muffler (forget the brand, but was recommended here) exiting towards ground before axle.

Anyway playing around, it used to exit out p/side before rear wheel, I liked the way it sounds w/just straight pipe. Will running just tube cause any engine problems? I would like to take the front cat out but it is that molded y tube collector from the exhaust manifolds. With the high mileage I wonder if it is restricting flow. It is a pretty good muffler itself. Any suggestions how to gut it? Building a replacement piece would be difficult and most muffler shops wont remove the cats. Would straight pipe, no cats, and turbo muffler be enough back pressure if needed? How much is needed? Of course will keep the O2 sensor.

Thanks for help, suggestion, opinions.

 

Ok, firstly, running without cats is illegal and can be dangerous from a carbon monoxide standpoint. So I will not recommend it, but it is your truck and you can do what you want with it.

If you are going to eliminate the cat, don't mess with gutting it. Gutting it will turn it into a big expansion chamber than will make your exhaust sound hollow and could hamper performance. Approach it from a standpoint of minimum turbulence. Minimize bends and sudden pipe size changes. If it were mine, I would mess with the cat unless there was something wrong with it. And at that point, I would replace it with a good high flow cat.

I like your idea of 2.5" pipe, if designed correctly that will produce a lot of torque.

I wouldn't worry about backpressure since you don't need pressure to run correctly, just velocity. You want the exhaust gases to move quickly through the system. Smaller pipes create more velocity, though you have to balance it against friction. The sides of the pipe create friction that will slow down the exhaust and create backpressure that in turn reduces performance as RPMs increase. As a general rule of thumb, you want to run the smallest pipe that meets the airflow requirements of the engine. I think 2.5" is a good size, though 3" would be excellent too.

 

I went to a exhaust shop and had them make me a custom y-pipe with a high flow cat.

 

Post a sound clip, we would love to hear it.

 

once i figure out how i will

 

Thanks for the replies.

I'm not opposed to running a cat, I just figured with 178k it can't be as free flowing as it was years ago. This front one is part of the y-pipe up to the exhaust headers and I it can't be cheap. Maybe a custom y like above and a high flow. How can you tell/test for the condition of an old cat like mine? Can't even see in it with a flash light when I cut the original pipe off next to it. Has a bend there.

Torque is what I would like. So 2.5" it will be. Any advantage to headers over stock manifolds without any other intake mods?

 

A cat does not become restricted or plug up with time or mileage. It will however become clogged up and eventually fail with lack of maintenance. I have vehicle with higher mileage and stock cats and they still run great. But once an O2 sensor goes out or some other condition that starts dumping fuel or oil, its all over. The large torpedos on the ford heavy duties do tend to fracture and clog themselves. It is a design flaw. But so long as that doesn't happen, the unit will perform just fine. The easiest way to post a sound clip is to post it as a video on youtube.