I know it's illegal to run without a catalytic converter but I can't seem to find a definitive answer if replacing the cats with a straight pipe will not let my engine run as smooth, lose low-end torque, and have worst gas mileage, or if it will have more hp, and have better gas mileage.

Mine are throwing out codes and I'm going to wait until I can barely run my car because now they don't seem to be slowing my car down

Let me know fellas please and thank you

 

Not sure about gas mileage will go down but you will definitely lose low end torque, car will be loud and annoying, it will stink. I dont recommend it not much benefit

 

Your car probably smells like rotten eggs when you accelerate. Stick them back on. If you don't have sufficient mods, straight piping is pretty much pointless.

 

I took mine out when the dealer wanted 1500 a piece to replace them. No funny noises, no loss of torque, i didnt notice any loss in gas mileage, but yes there will be foul smell if you start the car while in the garage. I drove it like that for 40 thousand miles before it got totaled.

 

leave them on... the stench is awful.

 

Please leave them on, like others stated before, it's not much benefit. Unless you have the right mods to make use of it.

 

+1 on leaving them on. I was running cat less for a while and the car smelled bad. Not only that, but it sounded raspy, and no power gain lol

 

Lol thanks I'm gonna go with some aftermarket cats

 

And what mods would I need to make use of deleting the cats?

 

Leave them on. Save a tree.

 

Turbo or supercharged... But not necessarily.

 

Also, considering I have borla mufflers and I want to delete the resonators when I replace the cats, what is the stock diameter of the pipes? If they're not 2.5in should I consider changing it to 2.5in?

 

Not much benefit removing the cats, less back pressure, so less low-end torque (not much). You'll gain a few horses, but not much there either. The car will also be a bit noisier. And even more if you decide to delete the resonators at the same time. Should give a nice sound though. The stock exhaust is too quiet anyways.

I believe stock piping is 2.25", but I am not 100% sure. I wouldn't change to 2.5". You'll lose even more low-end torque and thing will get very noisy (especially if you get stainless steel piping => more resonance than mild steel).

 

I was considering going catless when i ruined my cats by running rich for a few weeks.
Ended up getting 2 high flow carb legal cats (since im in cali) plus 2.5" piping from headers to cats then to tanabe medallian catback exhaust.
Sounds amazing and feels great. Plus low end torque is already too much, but then again i'm supercharged

 

It a nut-shell it's really not worth it.

#1 - It's illegal
#2 - It stinks. I've driven around without cats for years and never liked the raw gas smell
#3 - Gas mileage improvement? Wishful thinking (unless your cats are clogged which is rare).
#4 - You'll lose a bit of low end for a bit of high end. On a 300HP car, you stand to gain maybe ~1.5% in peak power (average power across the entire RPM range will be roughly the same)

Just don't do it... If anything toss a hi-flow cat on there and be done with it.

best of luck