Another question about Downpipes...

[saccocrap]

I feel like this topic has been posted about a ton, but I still can't really seem to find an answer to my question.

Long story short, I have an exhaust leak on my stock flex pipe, also the stock cat is either gone, or on its way out as I'm getting that classic sulfuric smell. So I need a replacement, I'm on a stock turbo, and everything that I'm reading so far says not to bother with a 3" downpipe, catted or not. Seeing as how I need to replace it anyway, and its not just for fun, will it really effect my performance negatively if I go 3" now? I'd rather not have to buy another DP when i eventually do go with a different turbo (whenever that may be).

Then is the question about catted or not. Most people on here seem genuinely concerned about emissions, which I am not, and the state of Maine doesn't require vehicles have any actual emissions testing (they just look for a check engine light) and I have my sticker license. So would there be any performance difference going catted vs catless? or is it simply down to the amount of turbo noises and smell I would notice?

Depending on which way I go, would it be necessary to update my vehicles tune because of the DP or would it be negligible?

Any help is greatly appreciated.

 

[gtx3076]

I have heard time and again that the stock downpipe is nowhere near its capacity on the stock turbo and the gains seem to marginal on larger turbos. The stock turbo itself is the restriction between the two. I personally don't care much about sound and if my cat was going bad, I would probably just get another stock one for cheap. I wouldn't consider 3" unless I was planning on upgrading the turbo.

 

[dhminer]

I’ve had several combos including:

Stock turbo - stock downpipe, 3” catted, 3” catless

S280 - 3” catless

2860 - 3” catted, 3” catless

In the process of installing a G25 with 3.5” catless with recirculating wastegate and 3.5” catless with screamer pipe. Eventually I’ll have someone weld a cat and recirc wastegate into the screamer pipe version.

I never noticed a performance difference on stock turbo regardless of what downpipe was on it. YMMV

Sound wise, the catless downpipe with stock turbo and Cobb cbe was by far the best sound. Minimal difference with the 2860 going between catted and catless. Catless smells bad but you get way more turbine noise.

I’d go ahead and get a 3” either catted or catless. I always keep a catted and catless downpipe which I swap for inspections just in case, but we’re OBD scan only here as well.

 

[akiraproject24]

If you cant get a stock one cheap, I'd grab a catted one or non catted if you dont mind the smell. You;ll probably want a defouler spacer to avoid CEL unless you spend a little more money and grab a high quality one like Milltek or Mountune (mountune isnt available anymore though new at least)

 

[akiraproject24]

But Whoosh catted with a defouler would probably be the lowest cost and good quality choice. It also fits way better than the milltek from what ive seen. I installed a milltek and its tight fitting

 

[Mega ST]

Bringing this back form the dead. I've been told on an S280 the stock down pipe is a definite restriction. Catless is best, but catted can work with less top end peak HP. I would love to do catless, but I hate the smell on Ethanol mixes. Straight E85 smells just fine to me. Kinda sweet like corn liquor. 93 smells awful. Does anyone have any data going from a stock DP to catless? Dyno or trap speeds? This data seems very difficult to come by of this forum/platform.

 

[Dpro]

Bringing this back form the dead. I've been told on an S280 the stock down pipe is a definite restriction. Catless is best, but catted can work with less top end peak HP. I would love to do catless, but I hate the smell on Ethanol mixes. Straight E85 smells just fine to me. Kinda sweet like corn liquor. 93 smells awful. Does anyone have any data going from a stock DP to catless? Dyno or trap speeds? This data seems very difficult to come by of this forum/platform.

My car was fast with s280 and Mountune Sportcat downpipe. That said , I do not believe the stock downpipe is as much of a restriction as some try to claim. Cars previous to you being on this forum where tuned with Turbo‘s pushing 375 hp on the stock downpipe. It’s been proven you should do more reading if you don’t believe it.

 

[Mega ST]

The purpose behind these mods is to be able to maximize power with efficiency . You can make good power on the stocker, but each mod that reduces restrictions even a little bit adds up. It becomes a game of inches. With a catless you should be able to make the same power with less boost than with the stocker. At least that’s how it works on my other turbo cars. It helps with spool too. More torque under the curve equals better trap speeds at the track. I’m shooting for 120ish. I’m trapping 110–113 as it sits depending on DA.