[RobZL1]

I realize there is a power limit to the stock primary cats (such as stock hp levels if you track the car all the time)...

But, for a car that doesn't see a ton of WOT, and will likely only see a maximum of 800-850 rwhp in the future...

What do we think about fabbing the stock cats into some 3" connector pipes behind a set of long tubes? I don't think I've seen anyone do that, but I'm thinking about saving some money over buying a set of Gesi Gen 2's and just repurposing the stock primaries behind a set of long tubes.

Would opening up the flow path to the cat with a large primary be of any benefit vs the tiny little 2.25" opening going into the cat on each bank in the stock configuration?

In other words, where is the real restriction here? The stock cat itself or the tiny opening between the tri-y stock shorties and the stock primary cat?

I think it would be interesting to see how a stock cat performs compared to a Gesi cat, if they were both in a set of 3" connector pipes after a set of 2" long tubes. We always talk about how restrictive stock cats are, but maybe a lot of it is due to the (relatively) tiny inlet and outlet in the stock setup, particularly when the gasses are so hot (and thus need more physical volume) closer to the head.

Thoughts??

[KingLT1]

Waste of time. The factory headers are far less restrictive compared to the OEM cat pipes. The most restrictive spot is from the header/cat connection to the cat. It necks down under 2" in that spot.

[SJFGTO]

No! Stock cats with long tubes on a supercharged vehicle is a recipe for cat failure and engine damage. Don’t be penny wise and pound foolish. Your ZL1 deserves better.

[RobZL1]

Originally Posted by KingLT1

Waste of time. The factory headers are far less restrictive compared to the OEM cat pipes. The most restrictive spot is from the header/cat connection to the cat. It necks down under 2" in that spot.

I probably wasn't clear. I meant to get rid of exactly that small spot. In other words, bolt up a set of headers. Take a piece of 3" off road connecting pipe. Cut the ends off the factory primary cats / fab up some reducer sections to put the factory cat in the 3" off road tubing.

So the flow path would be 2" primary to 3" merge-spike collector to 3" connecting pipe to modified factory cat with 3" inlet and outlet to factory catback (sans secondary cats).

[RobZL1]

Originally Posted by SJFGTO

No! Stock cats with long tubes on a supercharged vehicle is a recipe for cat failure and engine damage. Don’t be penny wise and pound foolish. Your ZL1 deserves better.

I'm not sure that's entirely true. If anything, it would present the stock cats with cooler gases. There is at least 1 guy running 800 through the stock manifolds and stock cats with no issues so far on a C7Z06

[SJFGTO]

Originally Posted by RobZL1

I'm not sure that's entirely true. If anything, it would present the stock cats with cooler gases. There is at least 1 guy running 800 through the stock manifolds and stock cats with no issues so far on a C7Z06

Stock manifolds are not long tubes. Re-read my response. Yes, it is certainly true. In any event, the issue has been discussed numerous times in past threads. Just trying to help avoid a known risk.

[RobZL1]

Originally Posted by SJFGTO

Stock manifolds are not long tubes. Re-read my response. Yes, it is certainly true. In any event, the issue has been discussed numerous times in past threads. Just trying to help avoid a known risk.

For some reason, I am not explaining this properly. I have never seen any discussion of running long tubes with stock cats. If you could point me to one of the numerous discussions I'd greatly appreciate it!

[LT4Greg]

If you are going to install headers then aftermarket cats would be the way to go. That’s my opinion.

[Joshinator99]

Originally Posted by LT4Greg

If you are going to install headers then aftermarket cats would be the way to go. That’s my opinion.

Yep, get yourself some GESI Gen2 cats if you really want to run cats.

[L78toLT1]

Originally Posted by RobZL1

For some reason, I am not explaining this properly. I have never seen any discussion of running long tubes with stock cats. If you could point me to one of the numerous discussions I'd greatly appreciate it!

You're explaining things perfectly, to me anyway, and i think you may be on to something. I believe there's more than enough objective evidence that no cats, with the exception of gesi gen2's will live in FI applications over 700ish whp. At Camarofest several years ago, toohighpsi told me that the stock cat strata was superior to anything else on the market - this was a few years before gesi gen2's were available. It would not be particularly challenging to fab a set of header connection pipes from a set of stock primary cats. Would they handle 850+ whp? It's possible. We already know nothing else, other than gesi gen 2's will. I think it's worth a try.

[Gunkk]

Originally Posted by RobZL1

What do we think about fabbing the stock cats into some 3" connector pipes behind a set of long tubes? ... Would opening up the flow path to the cat with a large primary be of any benefit vs the tiny little 2.25" opening going into the cat on each bank in the stock configuration?

Yes it should help you find the limit of the stock cat

Since almost everything in the aftermarket is garbage, why not try the stock cat. Let us know how it goes.

[RobZL1]

Originally Posted by L78toLT1

You're explaining things perfectly, to me anyway, and i think you may be on to something. I believe there's more than enough objective evidence that no cats, with the exception of gesi gen2's will live in FI applications over 700ish whp. At Camarofest several years ago, toohighpsi told me that the stock cat strata was superior to anything else on the market - this was a few years before gesi gen2's were available. It would not be particularly challenging to fab a set of header connection pipes from a set of stock primary cats. Would they handle 850+ whp? It's possible. We already know nothing else, other than gesi gen 2's will. I think it's worth a try.

Originally Posted by Gunkk

Yes it should help you find the limit of the stock cat

Since almost everything in the aftermarket is garbage, why not try the stock cat. Let us know how it goes.

This is exactly where I am coming from. I figure it's worth a shot. I like to tinker and DIY. It's my stress relief. I build it and tune it myself. To me it's also fun to think about and do something that others aren't doing every now and then. Sometimes it pans out, other times it doesn't. LOL

Either way, that's what I enjoy about this hobby. To me, the fun is in the build and the tuning and learning things. I used to log almost every daily 30-mi one-way drive on my 5th gen. I'd make little adjustments until that thing was driving smoother than stock with a cam, Big gulp, 103, headers, etc.

I'll probably fab up some stock-cat 3" connector pipes and see how it goes. The substrate of the stock cat is likely more restrictive than a Gesi substrate, but who knows by how much. If it fails, I can always buy some Gesi's and put those in there instead.

Thanks for the input! When I get around to actually doing it, I'll post the results, good or bad.

[Katech_Zach]

Catalytic converters need to be at their operating temperature in order to work efficiently. With long tube headers, they lose a lot more heat to the atmosphere than factory manifolds. You will not get your factory cats up to temp, and they will not function the way they do with OEM manfiolds.

There is also a risk you blow them out, they plug your exhaust, and you seriously harm your engine.

This sounds like a recipe for disaster in my opinion.

[JSH]

HPE installed green cats with their package, and they seemed fine. However, I roasted them with my KongX and they could be heard whistling as I went down the track. So, we scraped them out before dynoing my current package.

Does anyone make a hi-flow cat that will survive higher hp levels?