Straight Pipe Question

[Christian11]

I have a 2004 gmc sierra with a y pipe with cats and no muffler now. I am getting straight pipes done with no mufflers and was wondering if i cut my cats off would it mess anything up on the truck and if gas milage would change alot. There are O2 sensors in front and behind my cats. Any help would be great

[Carder09]

Now are you suggesting that you chop the cats and leave the sensors their, or remove all emissions system components? If removing all, I think you have to get it programmed so that the truck wont throw out codes and make your truck run like pop, now from what I have read on posts before is that the furthest rear sensors really aren't needed and they can go bad and not throw codes, but the main line sensors obviously can, so maybe someone with more knowledge can give you better advice on this since im a little hazy on this subject.

[tyhuck]

Yes, it will mess stuff up, unless you have a reprogram done that will delete the need for the last 2 O2 sensors.

[Christian11]

Thanks the mechanic thats going to do it said he could cut them out but i reckon he would leave the sensors all up there

[Doug_Scott]

One of the issues you will have is that the O2 sensors need a certain amount of heat around them to work properly. The cat does that. Some sensors are heated, but that was only to handle the few minutes it took the cat to get up to operating temp. Get some free flowing cats instead of just dropping them completely. The loss in low speed torque with high flow cats will be minor, unless you are going pro drag racing, not worth the effort.

[Christian11]

thanks man i am going to leave the cats up there for the time being and look into some high flow cats

[redvett]

OEM cats are high flow cats. Save your money. When you lower back pressure you raise the torque band and lower fuel economy.

[Big Whiskey]

Yes, keep the stock cats & O2 sensors. Just run your true duals from the cats back. Just so you know, it will sound mean as hell and cackle a lot...but you'll lose some low-end power and MPG. A set of glasspacks will keep the cackle, but give you some backpressure, which is what a stock engine needs.

[Christian11]

Thanks guys for the input im going to keep the stock cats i got the truck back and its loud enough for me

[Carder09]

Thanks guys for the input im going to keep the stock cats i got the truck back and its loud enough for me

 

So what exhaust did you get? I bought my truck with a section of pipe, about 10 in long, cut off and dumped under the truck with no muffler, and I was lookin to get a nice loud exhaust

[Mckenzie]

You might want to check into spark plug foulers. There was an interesting topic here about how you can use those to make your truck run as if it still had the cats

[Christian11]

I got true dual exhuast from the cats back with no mufflers and still have the stock cats. Its loud and has alot pop.

[GMstrong]

Probably sounds the same as bullets.

[Christian11]

It sounds good im pleased with it. Looking into some hi fow cats now