I know people are going to get mad and say to delete them and all that but I just hate the smell of no cats. I would consider upgrading them to aftermarket, probably GESI cats since that's the only aftermarket cat that I know is worth anything and I know they can stand up to the heat of high power FI.

I am kind of expecting to not find anyone who has done this but I hope there is at least someone out there. I am really wondering about light off and location given that with a turbo installed the cats are going to have to be pretty far down the exhaust line once everything is mounted up. I am also not sure where they will fit.

Also I've been searching everywhere and I've never had a GMT900 and not really familiar with them. But on my L9H Denali it looks like there is the normal cats then it goes to one pipe to a bigger cat looking thing that either is a resonator or post cat. Can anyone confirm? I don't think the 5.3s and 4.8s have this thing.

 

There are 3 cats on the GMT-900's. Two primary cats and a 3rd cat after the merge, in a way it is like another resonator but is a cat converter to help meet emissions standards. Both my 5.3's trucks had them.

Back in the day they had STS turbo kits that installed under the vehicle after all the emissions stuff. And now they sell turbo's they have their own lubrication system that doesn't require oil feed or return lines. You just have to get the charge piping up to an intercooler and into the throttle body. They are made by Comp Turbo's.

 

I crawled under it tonight and looked at it a little closer and I see it now, thanks.

I know the secondary cats on my 17 LT1 Camaro have 2 and they are a lot smaller, but it is ULEV. I know however if you take the primary cats off the secondary do almost nothing for unburnt hydrocarbon smell. I believe the main purpose of the secondary cats is for NOX or some other emission and it works with the stock GM fuel control feedback loop. So I would probably just keep the front 2 since I know those should keep down the unburnt hydrocarbon smell that sticks to your clothes and hair. Even though I would be running E85 99.9% of the time, from my experience even with E85 it still smells almost the same as regular gas unfortunately.

I remember the Squires turbos, I guess they went out of popularity I'm assuming since they were mounted so far they just couldn't make the same boost levels and people wanted more.

I've never really had a chance to see how a modern OEM turbo setup is. I am assuming they have the cats before the turbos? I would think cat light off would be more important to OEMs than turbo lag.

Because of this as well as throwing off the factory O2 feedback loop, I would assume not too many people are able to get the factory narrowbands and ECU to play nice with turbo exhaust setups, I am leaning more and more towards a supercharger again although I still can't understand why turbos can be so much cheaper than superchargers, but I guess Chinese haven't copied superchargers yet like they have turbos haha.

 

The OEM turbo setups are bolted or molded straight into the exhaust manifold and then the cats are after the turbo. Some cars don't even have exhaust manifolds, the cylinder head is it's own exhaust manifold that comes to a large square port that either a downpipe/cat bolts to or a turbo charger flange.

People have made the narrowband o2 sensors work, the placement just needs to be right. And usually you have to turn off the long term fuel control and only use the short term fuel trim along with tuning with a wideband.

 

The biggest issue with making big power thru cats is heat and unburned fuel. The first tuning session can be very hard on them

couple that with cheap/no-name cats, inexperienced tuners letting a lot of fuel into them and the owners beating the car hard and not letting the cats cool down and you have the recipe for the myth of "you can't make power thru cats"

I made 477 thru a bone stock exhaust on my GMT-800 Tahoe. It held up fine for ~10k mi before I pulled the blower for other reasons

with a turbo build, unless you do twins you will need to build a catted down pipe, so just spend good money on a cat long enough and 3.5-4" in diameter and I suspect you will be fine

 

I'm making over 600rwhp with cats but I'm supercharged. They are easier bc of very little lag, turbo setup would have to spool very fast to keep cats alive. That would seriously restrict your cfm and keep power production down. I daily my truck for work so I wanted it legal, it wasn't too hard but it did take extra effort. I think it could be done but the turbo size would be small or you'd have to gate the hell out of it to get it to spool...

 

My STS in sig was a blast to drive (except light throttle) but it had plenty of converter partly because of a ZO6 cam that didn't come on until about 3500. It had full exhaust only until where the muffler was. The GT67 was mounted in it's place. Boost was very quick but not like my blower. The dyno didn't work the day we took it. My Whippled 14 after he turned it down a bit only made 434 and 46x and ran 8.25 in that trim. (Better since) The 07 which weighed about 100 lbs more ran 7.64 on 8.5 lbs and I believe, had a 7.49 in it that night but didn't get to run again. All with factory cats. Higher boost may have changed that. I would keep 'em on low boost. Just my opinion...

 

Thanks for the help everyone. I would definitely keep stock exhaust manifolds, reason being is they keep in all the bad sounds that make your car/truck sound like a POS. So if I turbo I guess I would try to fab something by doing the passenger side exhaust manifold flip. I have a good MIG welder with C25 gas which does a good job and I welded up mufflers and other things on my Camaro exhaust. However, my weld skills aren't that great and it just seems like such a daunting task trying to fab up turbo downpipe and cats and getting them to fit in the small spaces available.

I know I have seen some people on here come to the conclusion after messing with them for so long that they think turbos are actually easier to install than superchargers. I hope its one of those things that seems extremely difficult at first but after you do it so many times you get really familiar and it becomes easy and you can't believe how hard you used to think it was.

 

So are you saying if you do twins there is no room to put cats on? or at least on the downpipes? I know my primary cats on my LT1 Camaro 6.2 are 4.5 in in diameter and I think they are the same ones on the ZL1.

I also wonder how much the turbo can help combust unburnt fuel? Like if you compared unburnt fuel smell with just a turbo with no cats and no cats with no turbo. Make me also wonder why there's never been any attempt to do some sort of nitrous or oxidizer injection or oxygen or air pump into the turbo. My suspicion is the unburnt fuel is not enough to do much unless you are running extremely rich.

 

Unburnt fuel hitting hot catalyst= fire in the cat= cat melt down

high EGTs can also cause damage

I was saying with twins you might be able to mate to stock cats in the Y pipe, but with a single there is absolutely no way; you need to build a catted downpipe