tdeweese

My current N/A setup is fairly normal/mildly aggressive. AI Heads, MAMO MSD intake, Johnson Short travel lifters, Katech forged pistons and 240/252 cam. I currently run AR 1-7/8" headers WITH CATS, in my area i don't need them for emissions so thought about replacing the X-pipe with the AR CATLESS system. Question is has anyone done this and did you see a HP and Torque increase and by how much by going CATLESS? Also was the car noticeably louder or highway drone increased?? Thanks Guys!!

Apocolipse

Makes the car louder, more rhasp, and a lot of decel burble / popping. Drone not so much.

jayyyw

Minimal HP/TQ difference with or without cats. ARH makes a good setup. They do help tone down drone. So, if you removed them, you'd likely notice; more drone, increased raw fuel smell at idle, decel pops and gurgles, exhaust flames are possible (i saw flames on nitrous with cats).

Unreal

Jay nailed it. Maybe 5-6hp, and it will be louder. May or may not have fuel smell.

Mordeth

I simply gutted mine then tuned out the rear 02s with HP tuners. Sounds better. Will only increase power in a meaningful way if the cats were clogged, otherwise maybe a few hp.

Dan_the_C5_Man

Cats ON please. I am no tree hugger, but I also don't want to breathe polluted air from unscrubbed exhaust, all in the name of 5 HP. Thanks.

zblackz06

Apocolipse and Jayyyw nailed it on the head.
I get that raw fuel smell,more gurgling and a little bit louder.

Indepth

I'm a child but I might be going back to catless from catted simply to get the gurgles and pops on decel back - I really enjoyed that part of being catless. It made down shifting all the more enjoyable for me.

The downside to being catless is definitely the smell at idle (especially if cammed). The sound of the car is definitely louder when catless, however, I noticed that with cats the idle seems 'smoother' in it's sound.

Basically, if you want full on race car noises and smells - go catless. If you want a slightly more refined driving experience with less smells and slightly less noises, go catted.

zblackz06

I will say I love the gurgling but it does get annoying after a long drive.

ls404fd

I'll be going back to catless on my next build because I miss throwing fireballs out the back :o

Also, I don't want to cut my very nice Kooks Green Cats out of my 2.5" when I build a 3" midpipe. It'll be more of a race build this time, and then going back to a more streetable setup in the future.

If you do want to run cats I highly highly recommend the Green Cats.

scramblerman

On my 2011 z06 with a healthy cam, pfadt long tubes, pfadt high flow cat x pipe, and stock catback, it definitely gurgles and pops on decel with the butterfly's open. Car is actually loud surprisingly. No nasty fumes at idle also.

Apocolipse

Im curious if the gurgle popping still happens when the flaps are closed and can break the mufflers 🤔

MOTOWN Z

Cats all day long! theres no real reason not to run them.

Apocolipse

Most of them break / rattle / melt when you start putting big power through them.

MOTOWN Z

Yeah you have a point there but it also depends on your definition of "Big" power , most I ever flowed thru cats is 761 at the wheels , now if I make 1200 at the wheels I doubt I would attempt to run cats , but on a stock LS7 I would absolutely run em.

Apocolipse

Another issue is quality - a magnaflow may hold up to your 700+ but some off shore brand may not last on even a stock engine.

jayyyw

Because nitrous!

jammeejamm

if you are on 91/93, run cats to help with the smell.

i may be a bit of a sissy, but just the smell and fumes were enough for me to switch to e85.

the smell from just backing the car into the garage was intense. my garage is detached, and even after the walk from garage to house i would get sideways looks from my wife when i opened the door.

Apocolipse

When you have a nice overlap cam...the smell clings to you if you walk behind the car...especially during warmup.

Indepth

Mine stares at me even with the cats because our attached garage butts right up to the kitchen. Apparently when I start the car in the garage and idle (even with the rear of the car facing the street) I shake the cabinets to the point our bowls, plates, etc. rattle. She told me this one day expecting me to be concerned and apologetic, when she got a response of a big smile and "that's awesome" she was not amused...

But, when I was catless the garage stunk even with the car pulled in instead of backed in. However, even with cats the garage still stinks, just not as bad - I have a big cam with a good amount of overlap though.