High Flow Catalytic Converter Experience & Options

[VMCB5S4]

Planning to start the Single Turbo Kit journey early 2023 and want to run a Cat as I'm tired of smelling like raw fuel every time I come home from a drive with the windows down.

I'm interested to hear other's experiences with High Flow Catalytic Converters. I've been looking around and was checking out G-Sport products: https://gsportbygesi.com/high-perfor...tems-products/

They are a bit pricey. I'm not looking to be EPA compliant but I would like to remove most of the smell without sacrificing too much power or killing my wallet. The single turbo setup will have a 3.5" downpipe. The rest of my 3" custom exhaust (from the mid-pipe back) I plan to keep. I've heard that a catalytic converter would be more effective if placed in the downpipe as it's closer to the heat source but I would like to have it where the midpipe meets the downpipe if possible. Less fabrication required.

Thanks!

[belms4]

I have a set of Autospeed 3" dps that initially had high flow cats. They were 200 cell I believe. They could never pass emissions here in Colorado, so I always had to swap to stock dps for emissions testing. I don't recall any smell or anything. So 200 cell took care of most of that.

I ended up gutting the cats in them to make them straight pipes since if I couldn't pass emissions with them I didn't see a point. I did notice a small gain on the butt dyno between the 200 cell cats and after when they were gutted. Definitely way more stink too, especially when the engine isn't warmed yet. But that car is mostly track duty these days, so doesn't bother me.

The ones you're looking at say 300 cell. If you're not worried about passing emissions you could go lower to 200 or less cpi. Will have a nicer growl out of the exhaust too the closer you get to catless. Maybe just me, but 300 cell doesn't seem too "high flow". More kinda between high flow and stock original cats.

As far as placement, cats work best at curbing emissions and smell when they're hot. If you can find room to fit them anywhere higher up than the midpipes then more power to you, but a b5 is pretty crammed up there as it is. They'll get hot in the midpipe placement, just takes a little more driving til they're fully up to temp. Not sure if I'd want to move these heat soakers closer to your turbo though. That was the issue with the precats on stock dps. They were like giant heaters helping burn up your turbos quicker and increase overall engine bay temps, especially once you upgrade beyond k03s.

Hope my info helps! I'm sure others on here have their own experiences with different setups.

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[Silverex]

I had techtronic catted down pipes and they did help with the smell some but surprisingly didn’t make a huge difference in sound. I was very hesitant about going catless since I like my car quiet but happy I made the switch. Biggest thing I noticed was spool and power…probably gained about 200-300rpms of spool and butt dyno said 10-15whp on my basic stg3 setup. While I know it helped with smell I don’t remember it being a big difference after taking them off….or I would have kept them.

[VMCB5S4]

Thanks belms! What a nightmare to swap to stock downpipes each time you have to do emissions. I'm lucky in NH. I still need to get state inspections annually but any car over 20 years old is exempt from the emissions portion.

I don't mind if I have to wait a little longer for the cat to heat up if it's at the midpipe to downpipe connection. The manifolds, up-pipe and downpipe are all ceramic coated. I intend to wrap all of those components with DEI titanium wrap and I'll use a PTP turbo blanket and wastegate blanket too. All of that should funnel the heat out down and into the cat even more.

I'll keep looking on my end. Hopefully others will chime in over time with their experiences as well.


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[VMCB5S4]

I had techtronic catted down pipes and they did help with the smell some but surprisingly didn’t make a huge difference in sound. I was very hesitant about going catless since I like my car quiet but happy I made the switch. Biggest thing I noticed was spool and power…probably gained about 200-300rpms of spool and butt dyno said 10-15whp on my basic stg3 setup. While I know it helped with smell I don’t remember it being a big difference after taking them off….or I would have kept them.

My current catless exhaust setup sounds fine IMO. The vibrant performance ultra quiet resonator and muffler take out almost all the rasp leaving a crisp tone. If I add a cat I'm not worried about sound change personally. I'm considering giving the GSport non EPA certified cat a try. I can live with the $200 range. Even if it tones down the stench at least 75% I could live with it.

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