Need input for hi flo cats

If the cats are well designed they should make fairly little difference. For all the more that people will talk about them restricting flow, if you look at how they are designed they should still maintain the same flow area as the pipe before or after them. That's why they are larger diameter than the pipe. The stock ones expand from 2.5" to something like 4" or more. A 2.5" pipe has an area of ~5 in^2. A 4" pipe has an area more like 12.5 in^2. That means the substrate inside could block off nearly 60% of the flow path and still maintain the same amount of flow area as the 2.5" pipe feeding it.

Generally speaking though the car should be able to adjust for it reasonably well. I know I talked with my tuner both when adding cats and when moving to 3" exhaust and he said there was no need to bother changing anything. The car did drive noticeably different to me initially, but the adaptives gradually bring that all back into line. Worst case I'd talk to your tuner about it if you are concerned. Guessing just taking cats out shouldn't make as big a difference as something like changing manifolds or exhaust size.

Some racing classes require cats on the car. The HP aftermarket has responded with high flow units to meet those rules.

Just curious, why are guys concerned with codes on a tuned car? Can't you just tune the rear 02 sensors out of it?

ViperZ06 said:

Just curious, why are guys concerned with codes on a tuned car? Can't you just tune the rear 02 sensors out of it?

Click to expand...

The answer: it depends.

You used to be able to do it with HPTuners. As of a couple years ago, they no longer support the ability to turn off emissions related codes due to Federal regulations.

Many shops won't touch emissions related stuff now for similar reasons. The regulations are being enforced, and the fines are pretty hefty for non-compliance. I know of one shop in this region that has alluded to the Feds stopping by in their social media posts, so even lesser known shops are feeling the pinch.

It is what it is.

Just to add some experience to this. I tried the flowmaster 200c cats on my car and it hated them. I'm going back to the no-cat life. Wish I wasn't as the fumes are, well, not ideal, but until I can find a cat that fits in the space that will work I'll go catless.

pMak26 said:

Just to add some experience to this. I tried the flowmaster 200c cats on my car and it hated them. I'm going back to the no-cat life. Wish I wasn't as the fumes are, well, not ideal, but until I can find a cat that fits in the space that will work I'll go catless.

Click to expand...

Similar for me. The smell on my car isn't super bad, but I learned very quickly that you don't let it run in the garage for very long, even with the doors open. I wouldn't mind the reduced volume they can offer as well, but I just don't have a good way to fit any that I think would survive. I guess I could go back to the factory manifolds with the front cats and keep the 3" race exhaust, but based on how hot the rear cats were getting when I tried them with my 2.5" setup I don't have high hopes the front ones would do any better, plus I'd be more worried they could hurt something being closer to the engine bay and wiring harnesses and the like.

MoparMap said:

Similar for me. The smell on my car isn't super bad, but I learned very quickly that you don't let it run in the garage for very long, even with the doors open. I wouldn't mind the reduced volume they can offer as well, but I just don't have a good way to fit any that I think would survive. I guess I could go back to the factory manifolds with the front cats and keep the 3" race exhaust, but based on how hot the rear cats were getting when I tried them with my 2.5" setup I don't have high hopes the front ones would do any better, plus I'd be more worried they could hurt something being closer to the engine bay and wiring harnesses and the like.

Click to expand...

Yup, I start it and immediately back it out of the garage and let it warm up outside. It wasn't a problem until I did a 3 hour trip in a LOT of traffic. With cars on either side, or a cement barrier on one side and car on the other side, the fumes were circulating in the cabin. I came home with a wicked headache.

The catted exhaust setup I had is stock front cats, gutted secondarys. I didn't like it because of the weight and heat. The setup I put on the car is titanium which carries the heat extremely well, but doesn't have cats. I tried a compromise with the flowmaster 200c pieces but they just don't flow - error codes pretty much immediately. I tried resetting adaptations, it doesn't matter, the cats are too poop.

You have a Gen 5. You're going to have exhaust code issues with pretty much ANY mods that involve the cats.

I'm no expert but not sure why it would. The front 02's I believe aid in that regard and the rear 02's I "think" just say if the cats are working properly. Again, no expert but I've done some rear 02 deletes on multiple cars where I changed the exhaust and then tuned out the rear 02's so as to not throw a code. I ran both with and without cats. I never had an issue. Viper could be a different can of worms. Seems like everything else is. lol

It's not a given that the car will throw a code. My car throws no codes with no cats and a fouler on the rear O2s.

I am a bit confused. I have the Borla Exhaust and JonB's high flow CATS. I thought the high Flow CATS with a better flowing muffler were supposed to cool things down?


Thanks!

John

High flow cats have a coarser mesh substrate that results in higher exhaust gas flow. Another result of this is that it does a poorer job of converting pollutant's into other gases, a lower percentage. Since they convert less, they generate less heat. They're just a way of keeping a check engine light off or getting by emissions testing. An OEM manufacturer can't us them because they don't meet regulations, let through too much pollutants.

No cats will be the coolest.

Stray Cat said:

I am a bit confused. I have the Borla Exhaust and JonB's high flow CATS. I thought the high Flow CATS with a better flowing muffler were supposed to cool things down?

Viper Parts Rack America

Viper Parts Rack America, for all of your Dodge Viper parts needs

www.viperpartsrack.com

Thanks!

John

Click to expand...

Yeah, that is generally true. The problem I have is that with my cam and tune the car just doesn't really like any cats. They work by effectively burning any leftover fuel from combustion inside them. They were designed with a factory tune and components in mind, so while they still run hot, they have the right amount of "stuff" in them to deal with what the engineers expected. Start adding more fuel to the mix (like a leaking injector or a weak spark plug or aftermarket parts) and they will start getting hotter because they are burning more unburnt fuel from the cylinders. Hi flow cats as Old School said are really just less efficient ones. Maybe some of them are designed to have the same amount of surface area with a better flow rate, but judging from all the pictures I've ever seen I highly doubt that as they are almost always smaller than factory ones as well. So they don't get as hot because they don't actually do as much work.

I just got my car back from Prefix which i have several posts on dif things. I did full Corsa cat back 3" free flow instead of 2.5" I think the cats they use Magnaflow cats? I can double check.

Car is back at shop and the pipe before cats is not hot but pipes from cat back is on fire so they are removing the cats and then checking tune.
This is on heads/cam car.
I had no issues with cats pre heads/cam.

Sniper said:

the pipe before cats is not hot but pipes from cat back is on fire

Click to expand...

This is the standard test every shop uses to check CATs, normal should be ~200F before, ~400F after, checked with an IR thermometer. Much easier on a non-Viper with everything exposed.

600F is usually considered Catalyst "light-off" temperature. That's the working temperature in the substrate, so you lose a little on the tubing.

Sniper said:

Car is back at shop and the pipe before cats is not hot but pipes from cat back is on fire so they are removing the cats and then checking tune.
This is on heads/cam car.
I had no issues with cats pre heads/cam.

Click to expand...

Did you end up removing your cats? What did you end up doing with them?
I bought mine catless with Tri-Y headers and Corsa exhaust and I love it. I kinda feel bad when I drive by homeless people and they get plastered tho.

Went catless and yes the sound alone is worth it!