I'm supposed to get my cats cut out tomorrow, I've been debating it for a while because the area I live in does not do emmision testing right now but rumors have been flying that they may succumb to government pressure and enact emmisions testing.
So the next alternative would to be an entire new Y pipe with no cats for the truck.
My question is would and increase in pipe diameter give me more flow to the STS turbo set up or would it compromise flow because the turbo has been sized to the stock exhaust pipe diameter and flow characteristics?
I'm thinking about going to 3.0" O.D. vs the stock 2.625"-2.75" O.D.s.

 

I don't know anything about turbos, but I thought I'd share something about the whole emissions testing thing. They just announced they're going to start doing that here in Austin, I thought "Oh, #$*%." But then I read the details: for vehicles equipped with an ODBII port, all they do is plug in a diagnostic computer and see if you're throwing any codes. That's it, no hooking to pipe or anything. What a joke. All ya need are some o2 simulators or maybe a Predator to clear yer codes! You might look and see what they may be planning in WI before you make a decision about your cats.

 

I have the cats shut off already in prep for my cats being cut out. My last Nelson tuned PCM had this done.
The other thing I have seen when getting emmision tested is the tester putting a mirror on a stick under the vehicle to do a visual inspection too see if you have modified your vehicle in any way. I know most of these people don't really know what the hell they are looking at but with my luck the guy who would check mine would be an expert and flunk me for no cats!!
Thanks for the feedback.
Tim

 

Ayone running a long tube header or modded Y pipe with an STS set up here? I'll bet there is someone............

 

If you gut the stock y-pipe you will pass visual....

 

I would go with 2.5" for the y into a 3.5 single

 

That would be good if you are N/A or supercharged, but with the StS I would want to keep the diameter smaller to keep the velocity up. I'd say on a 5.3 that 2" to the Y and then 2 1/2 to the turbo would help it to spool quick.

 

cant you just buy a sticker? Here in New York they changed it a year ago I pass every year.

 

cant argue with you there wasnt really considering the sts rear mount setup. I would still go 2.5 on the y pipe and 3" tail pipe having a bigger exhaust side is gonna help suck I would think it would also be better for a larger turbo.

 

The STS turbo mound is 2.5 isn't it? so I'd go with 2.5 for the cats (or what ever the stock pipe size is before the cats)
What size is the y pipe ?