who’s running cat converters with their LS Swaps

[72Z/28]

Hi guys

I am just tired of this exhaust smell after driving the car. Just wondering if anybody in this forum who has installed cat converters with their LS swaps.

Even for a short drive I smell like exhaust which os really anoying and cannot even take my family for a ride due to allergy issues of strong exhaust smell.

I have done some research and found a spun type high flow converter from Magnaflow ( 8” long and 4” diameter). They do have them in different inlets and outlets depending on the exhaust you ate running.

[JustJohn]

Exhaust smell is usually excess hydrocarbons - running rich.

[CSG]

Curious if your current exhaust runs all the way out the back? I have found that to make a big difference in how much I smell of exhaust after driving.

[saon]

I found a set of 5th gen Camaro take off cats on craigslist, someone swapping to headers on their car. I then cut out the smaller second cat and installed both on my 6.0/4l80 swap. zero exhaust smell. I also have my exhaust ran all the way to the back bumper. Just try to place the cats as close to the same distance as the factory did from the head to keep their temp range close. (this is why I used the second cat) your tune may need to be looked at afterward as well.

[72Z/28]

I am suspecting that it is running rich

[72Z/28]

Curious if your current exhaust runs all the way out the back? I have found that to make a big difference in how much I smell of exhaust after driving.

The exhaust is running all the way under the bumper.

[badazz81z28]

Exhaust smell is usually excess hydrocarbons - running rich.


Even when tuned the exhaust smells without CATs.

[badazz81z28]

Exhaust smell is usually excess hydrocarbons - running rich.


Even when tuned the exhaust smells without CATs.

[Reckn8]

We use Cats and don't forget a factory evap canister for when it sits in the garage!!

[junkyard]

I too am interested in the prospect of adding cats for both environmental reasons (I know that’s not popular) and odor. I've got an LS3 with an aggressive cam that sees occasional track duty. I keep hearing that the cats will over heat and become useless (or worse, break up and end up in the mufflers). Anyone have thoughts on that?

[badazz81z28]

I too am interested in the prospect of adding cats for both environmental reasons (I know that’s not popular) and odor. I've got an LS3 with an aggressive cam that sees occasional track duty. I keep hearing that the cats will over heat and become useless (or worse, break up and end up in the mufflers). Anyone have thoughts on that?


What research told you that? Doesn't the ZR1, Z28, Viper....basically any modern factory high performance vehicle that built for track use has CATS.

[CSG]

I know some forced induction cars have issues with cats if run hard for long periods.

[Reckn8]

High output cats work just fine! No worries!!

[oldstv]

I wish I had put cats on mine. I have two swapped cars and I will admit, one car smells pretty bad but the other one not so much. Both have pipes running all the way out the back. One car is a 480hp crate motor and the other is a stroked 427 with a larger cam. The 427 smells the most.

[junkyard]

What research told you that? Doesn't the ZR1, Z28, Viper....basically any modern factory high performance vehicle that built for track use has CATS.

That was my thinking - all modern high performance cars use cats, so why would it be an issue. My “research” consisted of just asking various engine builders/tuners in my area. All 3 out of 3 pushed hard to steer me away from the after market “high flow” cats, saying they’d burn up. I’m no expert, so I figured they knew something I didn’t.

[Reckn8]

So let me think about this. The factory's are pumping all this horsepower out and these guys are saying they will burn up? H'mmm

[CSG]

Problem is we are not talking about factory cars here. As far as I know we are not talking about forced induction cars either so the point is moot anyway. I can remember reading the instructions for a large company's supercharger installation that even in it said that above 5psi that the factory cat had to be removed. Quite a few guys with that platform blew the cat up. I also recall reading about the different tuning strategies required to keep a cat alive with forced induction. An OEM has no problem making a cat live in the car that does not mean we can just add one to any car and not have issues.

[TomMLS1]

Hi guys

I am just tired of this exhaust smell after driving the car. Just wondering if anybody in this forum who has installed cat converters with their LS swaps.

Even for a short drive I smell like exhaust which os really anoying and cannot even take my family for a ride due to allergy issues of strong exhaust smell.

I have done some research and found a spun type high flow converter from Magnaflow ( 8” long and 4” diameter). They do have them in different inlets and outlets depending on the exhaust you ate running.

If you have a rich condition, cats aren't going to make the smell go away. You need to have it properly tuned. I am running an LSA in my Nova with no cats and it doesn't smell at all. None of my cars have smelled bad, or any different than my truck running cats.

In addition, if you run cats, you really need to run the rear O2 sensors to correct fueling....just my opinion.

T,

[badazz81z28]

If you have a rich condition, cats aren't going to make the smell go away. You need to have it properly tuned. I am running an LSA in my Nova with no cats and it doesn't smell at all. None of my cars have smelled bad, or any different than my truck running cats.

In addition, if you run cats, you really need to run the rear O2 sensors to correct fueling....just my opinion.

T,


Are the rear o2s used for fueling??? I was always under the impression they were used to tell the ecm if the emission system was operating properly thus why they are commonly deleted with non -emission systems and the engine operates just fine.

[TomMLS1]

Are the rear o2s used for fueling??? I was always under the impression they were used to tell the ecm if the emission system was operating properly thus why they are commonly deleted with non -emission systems and the engine operates just fine.

And you would be entirely correct. Do not know what the hell I was thinking when I wrote that.....LOL

T,

[junkyard]

I too am interested in the prospect of adding cats for both environmental reasons (I know that’s not popular) and odor. I've got an LS3 with an aggressive cam that sees occasional track duty. I keep hearing that the cats will over heat and become useless (or worse, break up and end up in the mufflers). Anyone have thoughts on that?

For those interested, I did some digging around for high performance cats - extremely low restriction in flow as well as tolerance for very high temperatures. Vibrant Performance carries GESi cats that are supposed to be motorsports grade. They’re expensive as hell compared to other companies, (can be found on eBay for roughly 350/each) but hopefully they’ll be top notch. I won’t be welding them in for a few weeks, so can’t give an actual report on my experience just yet. Just wanted to pass along the info I came up with...

[CSG]

Kooks Green cat is also supposed to be good, not sure where the price falls.

[cdrod]

I'm looking at using a pair of these metal-core cats from Dynatech; they're $175 each. Anybody have experience with these??

146960

Specs say metal-core, 300 cells/inch, flow 396 cfm. According to my research, a metal-core cat can take the heat better than a ceramic-core cat, so rich AFR or lots of WOT driving won't burn them up. But they will get hot so heat shielding is a good idea. Also need to mount them as close to the engine as possible so they light-off quickly. My engine is a 400HP stroked Olds small block (375cid) with a FiTech throttle-body EFI in a convertible.

[CSG]

Spun metallic is what everyone recommended years back, I don't know if that has changed. Dynatech was well regarded but I believe that has changed.

[Later-A-body]

I have done exactly the same as you have proposed on my Pontiac LS7 swap. This was planned out from the start of the build. They are spun metallic versions from Magnaflow. I had stainless 3 bolt flanges welded to each end of the cats, which are bolted directly to the end of the collectors. This will allow the cats to fire off quickly. I also built heat shields that bolt directly to the underside of the transmission cross-member, and they are ceramic coated. The idea was to eliminate the smell, and it does. I have no exhaust odor at all. As far as I remember, each of these cats will handle approximately 450 hp (3" version), so the 600 or so HP I am making is well covered. I would highly recommend the installation. As far as noise, it made the exhaust a little quieter which I like, but it sounds fantastic when you nail it with the Borla mufflers. As for the tuning, you still need to tune the car well. Any over-rich condition will shorten the life of the cats. I specifically picked my cam to work with cats, which meant not going with a crazy amount of duration and overlap. As for factory cats, my good friend has a 2012 CTS-V making 800 HP, runs 10.80's @134, and it all runs through factory cats and exhaust. So maybe you can find some factory take offs if that helps.

[sheck44]

For those interested, I did some digging around for high performance cats - extremely low restriction in flow as well as tolerance for very high temperatures. Vibrant Performance carries GESi cats that are supposed to be motorsports grade. They’re expensive as hell compared to other companies, (can be found on eBay for roughly 350/each) but hopefully they’ll be top notch. I won’t be welding them in for a few weeks, so can’t give an actual report on my experience just yet. Just wanted to pass along the info I came up with...

Hands down the best, Ive used these on my builds ... In fact its a local guy here in Toronto that invented the GESI cats and now they are used worldwide on all sorts of equipment.

Cheers
Steve

[gnx7]

Exhaust smell is usually excess hydrocarbons - running rich.

Partially- but if you put cats on the car you won't smell like gas every time you drive the car. I put 3" dual Random Technology cats on a cam/headers LS7 in my 2800lbs RX-7 and it still went 10.30's@138mph with road race suspension. I hate that smell also. I would say with a 100-200 cell count performance cat you should lose 5-10rwhp depending upon how potent your engine is.

[badazz81z28]

Dumb question...would I need a new tune if I added cats?

[ddavisart]

Not a dumb question, I would retune to be safe. Alot of money in these pro touring builds and I would want to make sure everything is in line. I'm not sure if your running any FI setup but my previous supercharged 5th gen camaro saw boost drops when removing cats. Horsepower stayed about the same but less psi to put out the same number from the car now being less restricted. Now if you going the opposite way (tuned for no cats and you add cats) you would have the opposite effect and get more boost than your expecting which could be bad news if it causes you to run lean.

[ULTM8Z]

I have an EFI (non LS) and I've been running cats for almost 20 years now. Yeah the raw exhaust odor got old really fast. Just some high flow walker cats.

The only thing that would force a retune IMO is if the minimal change in exhaust backpressue caused a change in fuel demand. But in closed loop the ECM would easily correct for that. If the WOT fueling is open loop then a quick before and after peek with a WB O2 should tell you of your WOT fueling changed. My guess is it won't though...