[bigdonnyd40]

Hi folks,

So like many of you, I love the sound of a more free flowing exhaust with subtle burbles and running a tuned B58.

As we all know, the factory catalytic converter being right behind the turbo is the biggest bottleneck. The problem is that I'm sensitive to the gasoline smell of running catless and the catted options are very expensive, but more importantly, they all still smell and still add unneeded back pressure right behind the turbo. Also they deteriorate when you run burbles.

I recently had a catted downpipe (CG DS-1) and while the performance was there, the fitment was a little off and it smelled so I'm back to stock now.

My idea is the following: run a catless DP which allows for infinite burbles AND the best flow right behind the turbo, and to mitigate smell, run a downstream cat around the mid-pipe area. (possibly one of these).

This method is pretty popular in the Audi community as they have cats right behind the turbos as well. This should in theory mitigate smell IF the cats can get hot enough that far back from the turbo.

Would love thoughts on this.

Thanks!

[buddyboy]

Originally Posted by bigdonnyd40

Hi folks,

So like many of you, I love the sound of a more free flowing exhaust with subtle burbles and running a tuned B58.

As we all know, the factory catalytic converter being right behind the turbo is the biggest bottleneck. The problem is that I'm sensitive to the gasoline smell of running catless and the catted options are very expensive, but more importantly, they all still smell and still add unneeded back pressure right behind the turbo. Also they deteriorate when you run burbles.

I recently had a catted downpipe (CG DS-1) and while the performance was there, the fitment was a little off and it smelled so I'm back to stock now.

My idea is the following: run a catless DP which allows for infinite burbles AND the best flow right behind the turbo, and to mitigate smell, run a downstream cat around the mid-pipe area. (possibly one of these).

This method is pretty popular in the Audi community as they have cats right behind the turbos as well. This should in theory mitigate smell IF the cats can get hot enough that far back from the turbo.

Would love thoughts on this.

Thanks!

Yeah you could try that, where are you going to mount the 2 O2 sensors? You would need to extend their wiring looms and hope they work with the aftermarket cat cel.

You should not get any smell the cabin from a good quality sports cat. Even my cheap vrsf sports cat doesn't smell bad.

[bigdonnyd40]

Originally Posted by buddyboy

Yeah you could try that, where are you going to mount the 2 O2 sensors? You would need to extend their wiring looms and hope they work with the aftermarket cat cel.

You should not get any smell the cabin from a good quality sports cat. Even my cheap vrsf sports cat doesn't smell bad.

O2 sensors get mounted in the usual place when someone runs a catless DP - in the pipe where the cat would go. BM3 can disable the engine code caused by the post-st sensor.

The downstream cat would only be put in place only to reduce smell/emissions.

Obviously a sport cat would be simpler, but its placement causes it to deteriorate with burbles.

[mike@x-ph.com]

How will you handle the check engine light from the catless downpipe?

[bigdonnyd40]

Originally Posted by mike@x-ph.com

How will you handle the check engine light from the catless downpipe?

Removed with a tune (BM3)

[RonronEG]

The cat further downstream is still going to attenuate the pops and bangs, no?

I'd just buy a really nice high flow cat like the Active Autowerke, get the proper gaskets for seal and fitment and evaluate from there.

[I3LaZeN]

My vrsf doesnt smell in the car at all. Its when your outside of the car that you get a smell.

[mike@x-ph.com]

Originally Posted by I3LaZeN

My vrsf doesnt smell in the car at all. Its when your outside of the car that you get a smell.

No catless should smell in the car. if you smell fuel inside the cabin, that's a sign of a fuel leak.

[I3LaZeN]

Originally Posted by mike@x-ph.com

No catless should smell in the car. if you smell fuel inside the cabin, that's a sign of a fuel leak.

Yea I know. Some people report smells of it in car or when theyre at a light with windows down. I havent experienced that with my VRSF Catless.

[bigdonnyd40]

Originally Posted by RonronEG

The cat further downstream is still going to attenuate the pops and bangs, no?

I'd just buy a really nice high flow cat like the Active Autowerke, get the proper gaskets for seal and fitment and evaluate from there.

As I understand it, the burbles are caused by fuel igniting in the exhaust. I do not known exactly where it ignites in the exhaust, but logic would suggest that the further downstream the cat, the more likely it is to survive for a longer time.

My guess is that a cat at the midpipe section would still get hot enough to "light" the cat materials and reduce smell.

[buddyboy]

Do you have longer or more aggressive burbles enabled? The excessive burble thing gets old pretty quick in my eyes. I have a sports cat , Remus axle back, and just the natural B58 burbles can be overly loud at times.

You dont need to spend big money on a sports cat to get no smell, VRSF one has served me well for years, i have a new Opsrey performance 5 inch sports cat to go on next so interested to see how differs .

How much do you think the custom setup will cost? i wonder how having the sports cat cell that far down will have an affect on the exhaust flow?

[bigdonnyd40]

Originally Posted by buddyboy

Do you have longer or more aggressive burbles enabled? The excessive burble thing gets old pretty quick in my eyes. I have a sports cat , Remus axle back, and just the natural B58 burbles can be overly loud at times.

You dont need to spend big money on a sports cat to get no smell, VRSF one has served me well for years, i have a new Opsrey performance 5 inch sports cat to go on next so interested to see how differs .

How much do you think the custom setup will cost? i wonder how having the sports cat cell that far down will have an affect on the exhaust flow?

Hey. Great question!

So I'm actually going to get this setup going and will report back on my findings for the sake of modding posterity.

I purchase a catless DP. I went with ARM, but they're all around ~$200-$250. As for the high flow cat that will be installed right after where the downpipe connects to the mid-pipe, I'm going with a GESI UHO (ultra high flow) which is the same one that Active Autowerks uses. It is good up to 850 HP. There are two generations (gen 1 and gen 2) and the difference is the gen 1 is 300 CEL and gen 2 is 400 CEL. Gen 2 is designed for post 2016 emmission standards.

Part numbers for the Gesi cats are 85032 for gen 1, 85230 for gen 2. These are very high quality high flow cats, so they are around $700 each. (https://www.gsportbygesi.com/g-sport...stems-products)

Cost to weld in the mid-pipe cat is around $120 at a local exhaust shop (it's 3 inch inlet and outlet, so it should weld in easily).

So all in, it's ~$1100 which is around the cost of a higher end high flow cat. You end up with a burble safe catless DP right behind the turbo (in theory) and a very high quality high flow cat a little downstream that should eliminate the noxious smell and overall be a very good sounding setup.

I'll report my findings once this is done to the car.

[bigdonnyd40]

Originally Posted by buddyboy

Do you have longer or more aggressive burbles enabled? The excessive burble thing gets old pretty quick in my eyes. I have a sports cat , Remus axle back, and just the natural B58 burbles can be overly loud at times.

You dont need to spend big money on a sports cat to get no smell, VRSF one has served me well for years, i have a new Opsrey performance 5 inch sports cat to go on next so interested to see how differs .

How much do you think the custom setup will cost? i wonder how having the sports cat cell that far down will have an affect on the exhaust flow?

Also, in regards to your last question. I'm not sure how it will affect flow. I'll be looking to do a custom tune regardless, it shouldn't be much different than a high flow catted downpipe.

[Doctor X]

bigdonnyd40

If the smell of normal gas bothers you, I'd highly recommend running ethanol.

The smell overall is much more pleasant and less intense.

When I switch over to normal 91 my car wreaaaaks especially int he garage.