_zebra

iTrader: (5)

yeah, that's what i was thinkin' - ditch the driver's side.
and if it's anything like our '09 H3, the last cat ain't even monitored - it's just "there" (granted, ours also has the pipes on both ends flattened out from the factory for no apparent reason - so i'm thinking of just removing it in favor of round piping that don't constrict the exhaust).

shakenfake

Yeah I was gonna mention that as well, didn't think that cat was monitored.

jclark10

iTrader: (1)

Yeah I was planning on getting rid of the last cat. I think it's only there for Nox reduction and dosent do much for unburnt hydrocarbons.

But if I get rid of the drivers cat and just run the passengers side after the turbo at the downpipe, I would think it wouldnt be able to handle it and flow enough unless that's not what you're talking about?

I should probably just get a GESI aftermarket cat.

shakenfake

I'm saying run only the two passenger cats. Actually now that I think about it I would just run one passenger cat. I bet it would smell a tad but not like a whole bunch.

I would start with what you have before you go out and buy more ****. You would be wasting your perfectly good cats!

tjmath

If it were me and I was spending my own money, I would run a single cat after the down pipe. You are already going to be building your own mess of piping, why do the crossover from the drivers side manifold to the log manifold on the passenger side? I feel like that is the most logical thing to do here. Run the biggest hi flow cat you can find in the down pipe and if necessary do a second one 12-18" after it?

shakenfake

That is what I was trying to say I guess but you are better at words me to stupid to explain things good

_zebra

iTrader: (5)

i think we're all on the same page now.
the only downside to using the stock cats is if he plans to out-flow or overheat them - which goes back to my original comments on how much power he plans to push through them (especially with a turbo).

if you're moving enough air & fuel for upper-500s hp or more, stock truck cats will be on borrowed time. high-flow cats start becoming sketchy in the mid-600s.

not sure if the guts are different or not, but maybe he could find a diesel cat or two for cheap-ish that would be designed for that kind of airflow off a turbo.

shakenfake

I agree stock truck cats are on borrowed time but this will be a fine baseline for testing.

Proof of concept as one may say

smokinlmm

Just run obd1 cats...

jclark10

iTrader: (1)

So I am thinking about doing what y 'all are saying and just run one cat right after the turbo. GESI supposedly sell their "GEN2" (which they claim works for 2016+ emissions) "Ultra High Output" cat that is supposedly rated for up to 850hp for $451. I was thinking they were around $800 or so. This cat has a 4.5in body and 4in inlet so it should connect right up with my pipe out of the turbine.

Now obviously I'm not looking to make a turbo super high output partial zero emissions vehicle here haha, just trying to have no smell, I just care about the unburnt hydrocarbons and not about CO or NOx formation although they could be related, I believe the smell exclusively comes from the amount of unburnt hydrocarbons that escape. I had GESI cats on my 2017 Camaro when I had my Kooks headers and while they did take away the smell a good bit they still had some smell, they were also slow to light off not surprisingly as they were mounted to stainless headers but I can deal with a little sacrifice.

Doing this would let me completely preserve the stock exhaust system if I ever decide I want to go back. I really wish I could just find another whole and complete 2011 Denali L9H 6.2 exhaust and cats, then I could utilize what I can from my stock exhaust. With the millions of trucks out there with all these kids who love to run straight pipes haha you would think I could find one, I've checked muffler shops as well around here and most of them weren't too friendly haha.

I could also go ahead and start with a cheap Chinese cat to get me started and switch over once I get everything tuned and worked out, although it doesn't appear that I will be saving that much.