Kitty or no kitty

[GetAwayFromMe]

Finishing up my Stage 3 here soon and next comes the exhaust. Would i get any butt dyno from romoving the cats or hardly any? I'm debating if i should go catless or just stick with them.

If i'm looking at only 2hp gain than i should probably keep them because it will be somewhat more quiet. How loud really is the exhaustwithout them ? Can you chat it the car while driving? Last question, do i need to get o2 cell eliminators or just drill a hole in the pipe and put them there?

[01treyS4]

what kind of exhaust do you have?? it depends on what you have i have the ssac with cats removed and its fine in the car you can chat all you want...it gets loud when you step on the throttle tho..

[NogaroWonda00]

I think its a substantial gain but no idea what, you could also get hi flow cats. thats what I have, but I dont have any numbers to back it up yet.

you can scrap the secondary o2's if your going to get it tuned, they can just shut the code off so it wont throw the CEL, but if your not tuning it then you need them.

as for the sensor itself I dont think you could go wrong by placing them in a similar way as it would sit in the stock ones.

[MacDaddy]

pre cats generally rob the most power.

I personally hate the smell of hydrocarbons, so i would leave cats in place.

[GetAwayFromMe]

If there is no gains or no serious restrictions with cats in place than i would leave them on. I plan on Tracking my car and doing some highway pulls here and then so i dont want anything effecting my motor like not enough exhaust flow ect.

As far as the rest of the muffler it's going to be custom dual pipes no resonators or mufflers, straight pipes all the way back and than dual tips to finish it off.

[AudiA4_20T]

HUGE gains when taking out the cats... with turbos, the name of the game is flow... you need the whole system to breathe easy

[AudiSportB5S4]

^^ Agreed, I have piggies, test pipes and my Twin one... All that's in my exhaust is a muffler. It's really not THAT bad, the cabins of the audis are great they keep a lot of the noise out. And only once in a while you'll smell the lovely smell of fuel, but only with the right winds :).

[MacDaddy]

ASP says they rock cats on their website, look up the B5 S4 3" DP's.

[GetAwayFromMe]

Anyone have any logs or possibly dyno numbers with or without cats? If go without cats than i should look into some kind of a muffler at least.

[ENDEE666]

Removing my cats was one of my favorite $ for $ mods... Get rid of em!

Cats are for Pussies

[RolledMySTi]

The under car cats are fine and you should leave them in. It's the cats in the downpipes that kill performance.

[GetAwayFromMe]

Eyes on me bitch can you hear me rolling through the hood loud as fuck lol Another thing is i dont want to atract cops with my loud muffler scaring babies.

I will leave the cats on and see if it's hurting my preformance. I should have my muffler shop make me a quick disconect right before the cats so when i go to the track i can take them off. Orrr.... Maybe i need to invest in a cut off muffler :)

[ENDEE666]

Main cats DO hurt performance big time, but removing them does not automatically mean you will be loud. My car is VERY quiet, and I have no cats at all. Its the rest of the exhaust that matters most. My car is almost silent when cruising, nice tuned sound when you get on it. No cats and all mufflers are straight thru... Size of them is key..

[GetAwayFromMe]

Main cats DO hurt performance big time, but removing them does not automatically mean you will be loud. My car is VERY quiet, and I have no cats at all. Its the rest of the exhaust that matters most. My car is almost silent when cruising, nice tuned sound when you get on it. No cats and all mufflers are straight thru... Size of them is key..

No cats and 2 1/4" all the way back does that sound loud Take in note that this is dual 2 1/4" all the way back.

What did you do with your rear o2 sensors? Tuned the engine light out or??

[MacDaddy]

dual means two, duel means a match between two rivals.

[GetAwayFromMe]

dual means two, duel means a match between two rivals.

hahaha thanks man i kinda knew i was spelling it wrong i was just lazy to look it up.

[AudiSportB5S4]

No cats and 2 1/4" all the way back does that sound loud Take in note that this is dual 2 1/4" all the way back.

What did you do with your rear o2 sensors? Tuned the engine light out or??

The CEL can be coded out from a custom tuner, he uses SSP so yeah, it's coded out .

[GetAwayFromMe]

If were to leave the cats i would be loosing what? 10hp? If so i dont think 10hp is worth the fine i would get if i get pulled over.

[blmlozz]

If were to leave the cats i would be loosing what? 10hp? If so i dont think 10hp is worth the fine i would get if i get pulled over.

less than that.. probaly more like 7-8HP @ 400AWHP, and about half that with a high-flow performance cat.

Virginia has CAT checks every year for their inspection, so I'm getting primary cats in my DP's from JHM. Plus, I got tired of the smell of hydrocarbons as well, it's fun the first time but is pretty lame when you're sitting in traffic and all you can smell is fuel. Dirties up the rear of the car too.. and that's lame as well.

[o3spec]

if you are running high boost on ko4s you will see alot of gains from cat-deletes. the turbos won't run outta breath so quickly. so in other words if your going to run 19+psi (est.) you will see pretty big gains on your topend. but if not you will still see some gains but not as noticable. plus the smell isn't so bad, you only smell it when you go in reverse, and briefly when you come to a stop with the windows down.

[GetAwayFromMe]

-If it's only that much than who cares i'll leave them bitches on. We dont have inspections here in Iowa but no cats is ilegal and i think the fine is near $200 while fine for loud muffler is only $50.

I just dont want to run into any problems with my turbos because my exhaust didnt have enough flow and stock piping is alos kinda small.

[GetAwayFromMe]

I will be running 19+ PSI I should look into hi flow cats that would help instead of deleeting them. This is driving me nuts. I will be putting my motor back in i a week or so and i still cant decide

[o3spec]

-I just dont want to run into any problems with my turbos because my exhaust didnt have enough flow and stock piping is alos kinda small.

as long as your pre-cats are taken out, and you don't run really high boost you will be fine. but if your want to run 22+psi atleast get some cutouts. otherwise you may put too much strain on a already sensative turbo.

[o3spec]

if i could do it over again. i would go 3" dp with high flow cats and electric cutouts

[o3spec]

I will be running 19+ PSI I should look into hi flow cats that would help instead of deleeting them. This is driving me nuts. I will be putting my motor back in i a week or so and i still cant decide

i would do high flows at the very least then. you should be fine unless you go real high. you would see good gains if you deleted them though. it really isn't as bad as other cars ive owned with deleted cats.

i vote highflow or delete, definatly

[GetAwayFromMe]

Since you have Marcs tune what is his boost set at? I got his fueling kit but my motor is out so i didn't have a chance to run it yet.

What about stock piping? 2.25" is kinda small right?

[o3spec]

i run a daily 22psi. but i run 24psi on "weekends". and all this is on his ots fueling, i haven't changed a thing on his tune yet. i would talk to marc about the dp's size though. i would think piggies would be fine but i have custom 2.5" piggies since ive been stg3. so i don't know if 2.25 is good enough or not.

[o3spec]

Since you have Marcs tune what is his boost set at? I got his fueling kit but my motor is out so i didn't have a chance to run it yet.

What about stock piping? 2.25" is kinda small right?

you run a mbc with marcs tune. so the boost is set to whatever you'd like

[blmlozz]

Since you have Marcs tune what is his boost set at? I got his fueling kit but my motor is out so i didn't have a chance to run it yet.

What about stock piping? 2.25" is kinda small right?

2.25" is just fine for 250horse.. but for anything more than that you'll see gains with bigger piping, it's usualy about 5-10horse on k04's.. which is why people do piggies, because at $875 that's $87.5/hp at the max. Not very cost effective.

[lnferno]

Does anyone have any before and after dynos of cats and then without cats?

[GetAwayFromMe]

you run a mbc with marcs tune. so the boost is set to whatever you'd like

hmm.... I dont rememember him telling me that i need to a MBC so i will have to ask him about that.

[fatezero]

I have the FI Wide Mouth DP's with straight pipes and I also got a set of their 100 cell high flow cats and their is no noticeable difference except sound. I can tell a slight difference on the top end, but that's it.

[panix73]

I just deleted the cats and resonator on my noggy (stock exhaust) this weekend. All that is left is the stock s4 muffler. It's not much louder than with the resonator and cat setup, at idle and cruising speed. Two 2 1/4" downpipe test pipes to 3" straight to the stock muffler.

Although for the most part, even [I]during[I] full throttle it's not as loud as something you may hear from an idling EBAY rice muffler (lol), but it doesn't need to be in order to feel and sound great. To me it's still quiet enough to have civil conversations in the car, although as you go deeper into the throttle and begin to build boost, you'll notice that there is just a little more kick to it and all of the sudden the car just becomes to coming alive. You'll notice the throttle response gets much crisper and there is just a little more *umf* to it. To me this "stealth" exhaust is perfect for someone who appreciates the the natural tone of this car's exhaust, although doesn't want it bleeding through their ears!

[Audi S4 Turbo]

you run a mbc with marcs tune. so the boost is set to whatever you'd like

Well you can run it in parallel with the N75. So you have the called 22 psi or under. N75 will only allow what the tune is good for. If you run it in stand alone then you can.