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Discussion Starter #1
Just an FYI...

Been looking at high flow cats for a while... decided I'm going with high flow cats and the full Renick catback before I have Scott tune my car. The two options I was looking at for high flow cat downpipes were AFE and ZZP.

The AFE high flows have provisions for the stock downpipe rear brace that connects to the transmission, already have an extra bung for a wideband, and look extremely nice... but they wanted $1282 for them. yikes!

The ZZP high flows don't have provisions for the rear brace nor an extra bung for the wideband, but they are only $499. I was planning on buying the ZZP downpipes and fabbing and TIGing on my own 304 stainless brackets on for the rear brace and adding a bung for the wideband at the same time.

Last night I was looking again at downpipes and the Renick catback and noticed AFE has their high flow cat downpipes on overstock 50% off sale for $641. I decided paying an extra $142 for the AFE's was worth it to save me the time fabbing and welding the rear brace brackets and an extra bung on myself.

Link if anyone is interested... https://afepower.com/afe-power-48-34128-hc-twisted-steel-down-pipe
 

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2016 ATS-V Sedan 6MT
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That's not a very good location (post cat) for a wideband, but overall they look like a higher quality component compared to ZZP that I just installed on my car. Make sure you buy new turbo to downpipe gaskets and nuts, they're not reusable.
 

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Discussion Starter #3 (Edited)
That's not a very good location (post cat) for a wideband, but overall they look like a higher quality component compared to ZZP that I just installed on my car. Make sure you buy new turbo to downpipe gaskets and nuts, they're not reusable.
Yep, already have new nuts and gaskets on order. GM says the nuts are one time use, probably crimped or taper locking. There's also a PI out for replacing the rear brace nuts with locknuts as those have been known to loosen and/or fall off and lead to ticking (it's referenced on the turbo rattle bulletin.) Noticed that mine were ready to fall off when the car was on the rack for the last oil change, I need to get the updated taper locknuts.

I agree that post cat isn't an ideal location for a wideband and pre-cat is the ideal location especially when tuning cruise where things are near stoichiometric or slightly lean, but when tuning WOT there is usually only a small difference in pre vs post cat wideband readings since there isn't enough free oxygen in the exhaust at a rich WOT mixture for the cat to do its thing. Plenty of successful tunes have been done with a wideband post-cat in a bung or in a sampling probe in the exhaust tip (I don't care for sampling at the exhaust exit for lag time reasons, although others do it.)

Also, access between the turbo outlet and cat inlet is rather tight on these cars; I'll certainly see if there's room and if so I'll add my own extra pre-cat bung. I have plenty of 304 stainless O2 bungs and lots of 308 filler rod for my TIG, it'll take longer to pull out and setup the welder and backpurge bottle than it will take to add the bung. The other option is to disconnect one pre-cat factory O2 sensor and stick the wideband in one of the pre-cat bungs and temporarily disable all the primary O2 sensor codes on that bank during tuning, and then when finished put the factory pre cat sensor back in and re-enable all those codes.
 

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Discussion Starter #5
I've welded my wideband bung to the left of the upper bung on the passenger side downpipe. Fits just fine!
Good to know. I haven't had my car up on the rack in about a month and a half, so I was going from memory. I know with the large factory cats and nearby heat shields things are rather tight, sounds like with the high flow cats being smaller there's more room for another bung pre-cat. I'll know for sure once I have the car up on the rack to remove the factory cats and test fit the AFE's.
 

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There's plenty of space between the transmission tunnel and passenger side downpipe. Just have to find an appropriate angle where the wideband won't hit anything and mark it well. My buddy that did the welding used a long socket as a placeholder for the sensor to find the ideal spot.

For your wideband, have you planned the routing of cables? I ended up feeding mine through the driver side fender since that's the side where my gauge/controller is mounted. This method required no drilling, I've used existing holes.
 

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Discussion Starter #7
There's plenty of space between the transmission tunnel and passenger side downpipe. Just have to find an appropriate angle where the wideband won't hit anything and mark it well. My buddy that did the welding used a long socket as a placeholder for the sensor to find the ideal spot.

For your wideband, have you planned the routing of cables? I ended up feeding mine through the driver side fender since that's the side where my gauge/controller is mounted. This method required no drilling, I've used existing holes.
I'm only going to use the wideband for tuning, not going to be a permanent install. On the dyno the wires can drop out and under the car, if I do any drive logging I'll find some spots to ziptie and painter's tape the wires in place temporarily to get them into the car to the laptop.

My tune isn't going to be crazy since I'm limited to 91 octane. I recently found there's a new E85 station 12 miles away that's tempting though (previously used to be a 37 mile drive 1 way for E85), but if I go E85 that means a big round of upgrades... larger fuel pump lobe cam, larger DI pump, possible new LP pump, flex fuel sensor, etc. And if you're in it that far might as well do the larger turbos once they're available and take full advantage of E85, LOL
 

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I'm only going to use the wideband for tuning, not going to be a permanent install. On the dyno the wires can drop out and under the car, if I do any drive logging I'll find some spots to ziptie and painter's tape the wires in place temporarily to get them into the car to the laptop.

My tune isn't going to be crazy since I'm limited to 91 octane. I recently found there's a new E85 station 12 miles away that's tempting though (previously used to be a 37 mile drive 1 way for E85), but if I go E85 that means a big round of upgrades... larger fuel pump lobe cam, larger DI pump, possible new LP pump, flex fuel sensor, etc. And if you're in it that far might as well do the larger turbos once they're available and take full advantage of E85, LOL
Larger turbos are readily available but it's a lot of money to get there. I'm in the same boat with the 91 octane so I'm only doing an intake, ZZP catted down pipes, and tune on my car for the time being. When this car is no longer my daily driver, I'll likely shoot for 700 WHP with a custom EFR twin-scroll setup.
 

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Just an FYI...

Been looking at high flow cats for a while... decided I'm going with high flow cats and the full Renick catback before I have Scott tune my car. The two options I was looking at for high flow cat downpipes were AFE and ZZP.

The AFE high flows have provisions for the stock downpipe rear brace that connects to the transmission, already have an extra bung for a wideband, and look extremely nice... but they wanted $1282 for them. yikes!

The ZZP high flows don't have provisions for the rear brace nor an extra bung for the wideband, but they are only $499. I was planning on buying the ZZP downpipes and fabbing and TIGing on my own 304 stainless brackets on for the rear brace and adding a bung for the wideband at the same time.

Last night I was looking again at downpipes and the Renick catback and noticed AFE has their high flow cat downpipes on overstock 50% off sale for $641. I decided paying an extra $142 for the AFE's was worth it to save me the time fabbing and welding the rear brace brackets and an extra bung on myself.

Link if anyone is interested... https://afepower.com/afe-power-48-34128-hc-twisted-steel-down-pipe

Mandrel Bending Solutions has stainless steel metal matrix cats for a great price [~$125 each]. I use the 200 cell heavy loaded ones and have run 10.77 @128 mph. They flow over 500 cfm.
 

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Just an FYI...

Been looking at high flow cats for a while... decided I'm going with high flow cats and the full Renick catback before I have Scott tune my car. The two options I was looking at for high flow cat downpipes were AFE and ZZP.

The AFE high flows have provisions for the stock downpipe rear brace that connects to the transmission, already have an extra bung for a wideband, and look extremely nice... but they wanted $1282 for them. yikes!

The ZZP high flows don't have provisions for the rear brace nor an extra bung for the wideband, but they are only $499. I was planning on buying the ZZP downpipes and fabbing and TIGing on my own 304 stainless brackets on for the rear brace and adding a bung for the wideband at the same time.

Last night I was looking again at downpipes and the Renick catback and noticed AFE has their high flow cat downpipes on overstock 50% off sale for $641. I decided paying an extra $142 for the AFE's was worth it to save me the time fabbing and welding the rear brace brackets and an extra bung on myself.

Link if anyone is interested... https://afepower.com/afe-power-48-34128-hc-twisted-steel-down-pipe
Whatever AFE is smoking, I want some, who the hell is paying $1200 for downpipes
 

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Discussion Starter #11
Mandrel Bending Solutions has stainless steel metal matrix cats for a great price [~$125 each]. I use the 200 cell heavy loaded ones and have run 10.77 @128 mph. They flow over 500 cfm.
Odd, the only high flows showing up for me on their webpage are the diesel high flow cats; all the other links for the 50, 100, and 200 cells go to blank pages. I thought about making my own downpipes with 200 cell cats for more flow, but decided to stick with 400 cell cats mainly to keep the noise level reasonable and the 3000rpm rasp under control while still picking up some flow over stock.

Did you hack up the stock cats to get the turbo flanges, or did you fab complete new downpipes?


Whatever AFE is smoking, I want some, who the hell is paying $1200 for downpipes
Probably nobody, which explains the 50% overstock price... LOL. The current price is much closer to reality, not much more than the ZZP's. I received them yesterday, they're made extremely well. Tube fitment looks great, flanges are nicely done and ground flat, welding looks very good with no inside oxidation/"sugaring" so they were backpurged properly while welding, etc.

Still trying to decide if I want to do the Renick oval midpipe + stock muffler, or the full Renick catback. I'm strongly leaning towards the full Renick catback but am waiting for sclayton to post a couple more videos. :)
 

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I might just have to pull the trigger on this one, as I start to compile parts for the imminent early powertrain warranty termination.

If we are talking about a 400 cell cat, which is quite generous, as far as aftermarket cats are concerned, does anyone know what the stock cats density is? I know that lower cell density doesn't necessarily translate into better flow, but it is a somewhat of an indicator if it is a well designed cat.
 

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Discussion Starter #13
No idea on the stock cat density, but the stock catalyst brick is rather long, and there are some sharp bends and creases in the factory downpipes. They wouldn't appear to flow well at first glance, but the car makes pretty damn good power through them even in stock trim...
 
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