[Sniz]

I've been pondering which way to go with downpipes. My 2 options are to go catless and keep the stock secondary cats. That would require an O2 simulator such as Terry's or the built-in capability of the Procede (once Shiv releases it). Or to go with catted downpipes and remove the secondary cats.

Has anyone tested both configs to see which give the best power gains? The best sound?

Going catless downpipes and keeping the secondaries would be the most cost effective, but would it give the best flow? The cats that would be used would be the stock units, not high flow versions. also the "blockage" of the cats would be moved furthur downstream in the exhaust which should give the entire exhaust better breathing characteristics.

However going with catted high flow downpipes would mean the only cats left on the car would be high flow versions.

What do you guys think? I do not want to go completely catless due to noise and smell. I'm a bit torn on this one.

Comments?

[jbttum3]

Are you definitely keeping the stock exhaust? If so, get the catless DPs. If you are thinking about getting a catback system, then Catted DPs might be your only option....Don't think any of the catback systems for our cars come with cats. I have the Catted DPs with AA catless exhaust. Sounds really good to me. Quiet enough when cruising but you can definitely hear it when you open up the throttle. Plus I haven't thrown any CELs

[Sniz]

I may keep the stock exhaust and just modify it a bit......change the rear section including mufflers and tips.

OR

I have a guy ready to make me a custom full stainless exhaust using magnaflows. He could add in a set of high flow cats in the exhaust letting me use catless DP's if they make more hp.

[e90AW335i]

I would go with catless DP's and then put racing high flow cats as far back in the exhaust as possible. I think this would give you the best of both worlds.

[XPO186]

subscribed

it's either/or for me as well, but not sure if I want to keep the resonator too

[chinoxs203]

i would say catless DP's and rear muffler section will get the best gains,

[Sniz]

Catless DP's and intake are on order already for Ultimate Racing. I'll report back after installed and dynoed.

[longodj]

That was a good choice, don't forget that cats under the hood raise temps. Putting them under the car will keep your engine nice and cool

[Mr. 5]

Originally Posted by Sniz

Catless DP's and intake are on order already for Ultimate Racing. I'll report back after installed and dynoed.

You made a very good decision.
This is what I would have done if I were to do it all over again.

[XPO186]

Originally Posted by Sniz

Catless DP's and intake are on order already for Ultimate Racing. I'll report back after installed and dynoed.

Originally Posted by TheShuke

im going to do catless dps (with o2 simulator) and do a rear sect 3 as well and leave the rest stock.

please post some sound clips and videos when installed... I'm thinking about this setup as well... I may also do an HFC downstream from the DP