On a 1991, is there any risk in removing the cat converter? Will it cause sensor problems? Anything I need to do or be aware of? I do not have to pass emissions where I live.

 

If your cat is not bad, leave it on. If you remove it, chances are you will have to deal with strong exhaust fumes in the cab from the exhaust. That is quite common. But to answer your original question, no it won't hurt anything sensor related.

Overall, what are you trying to accomplish with your exhaust?

 

Had a friend that recommended I remove them and go with straight pipes. The previous owner removed the muffler. I have about a foot of pipe coming out of the second cat. The exhaust fumes come into the cab. We were discussing options and he said it would run fine and sound great without the cats. I am good with wrenching on the engine but I have never worked on the exhaust system. The rear cat looks to be easily removed but the front cat looks to be directly connected to the manifold on the left. There is a coupler where it connects to the right side. If I left the cats in I need to extend the tail pipes to the rear of the truck. I would really like to improve the sound though.

 

Another question. The truck is rather quiet the way it is. Will a cat back system improve the sound?

 

Cats do a lot to quiet the system down, factory mufflers quiet it further, removing anything with make it louder but not necessarily better. I have one cat and a flow master on my 351W and I like the sound quite a bit.

To answer your other question, yes the first cat is integral to the Y-pipe. You can "gut" it which turns it into a pipe basically, or cut it out and weld in a pipe, or change the Y-pipe out completely. All of those options are kind of a pain in the *** so if its not all rusted out and jacked up I would just throw a muffler on it with a pipe routing it out the back and call it a day. The bolts connecting the y-pipe to the manifolds like to snap off when trying to remove them.

 

Sounds the you have a V-6, I have a straight 6 in mine. My muffler was crappy and I cut the pipe right at the cab. Power increase was noticeably when I cut the muffler off and she got louder meaning sound lol. I do have immisions here in NM but only visual so a buddy told me to basically cut the cat open and hollow it out so it only has the visual aspect to it and then where the end of the pipe is turn and side pipe it in front of the right rear tire. So I may take that course of action.


Dutch
ABQ, NM

 

They didnt make a v6 in these trucks

 

Thanks! I'll leave the front cat alone. Would removing the rear cat and adding a flowmaster improve the sound?

 

Adding a tuned muffler like a flowmaster will change the sound characteristics boosting certain tones while canceling others. That along with pipe diameter and length and air flow is what gives you your sound. The cat doesn't necessarily reduce sound but it does attenuate. Notice how loud some 4 bangers get with the cats still in tact. Think of the exhaust like a brass instrument. Bigger horns sound deeper. Too big and you can't get enough air speed for the engine to perform or the sound to travel. A good rule of thumb for the 4.9/5.0L motors is 2 1/2" dual or 3" single pipes. Pick a muffler sound you like then add a short pipe for maximum volume or a turnout if you prefer. I used a 90* to eliminate freeway drone. To broadcast farther making the volume appear louder add a megaphone tip. Use a flair from your 3" to whatever size you like. I've seen 5" tips at Autozone. Headers help a lot as will reducing intake restriction. However remember when you are messing with anything it effects the engine performance. Too big an intake and throttle body will loose you torque. Then there is the warm air vs cold air and high vs low pressure debate you can find all over the board. And the same at the other end. Too open on the exhaust and the gas velocity slows down reducing scavenging, torque and mpg. Finally keep in mind a 6 cylinder sounds like a 6 cylinder no matter what you do. Also as someone who has studied as a smog tech and someone who likes HP I recommend keeping the cats. They really do clean a lot of dangerous stuff that you and your loved ones will be breathing when you drive and they don't rob any power unless they are damaged.

 

Removing the one or both cats will free up that 5.0 like crazy! The best mods you can do to a 5.0 is 1. lower gearing and 2. replace y pipe with a high-flow one. What you can do is remove the rear cat all together or replace it with a high-flow cat. Adding any flowmaster muffler will improve the sound over a stock muffler, so yes it will be louder and more throaty.

For my setup, Im going with a Magnaflow Y-pipe with one highflow cat (eliminates 1 cat) and a Flowmaster cat-back dual exhaust system.



I took these not too long ago, just waiting to be installed:





And the cat-back system I have already on the truck: