I am wondering if anyone can help me make a decision on installing sport cats vs adding a cat back system. My C8 is a Hypersonic Grey HTC Z51 with NPP and optional black exhaust tips, which I really like and would prefer keeping. I would have to have either set up installed by a professional, but I am just wondering if the cats would be easier/cheaper to have installed. Also, are hi flow cats going to cause CEL issues or fail smog certification when it time to have it certified?

I am a frugal bastard and I am leaning toward having Corsa Sport Cats(or similar) installed to my stock exhaust since I understand they improve the sound. I'm not looking for a crazy loud system, just something a little more unique that the stock sound.
It appears that sport cats are in the same price point as some cat back systems. I also see they sell cat heat wraps separately which are also quite expensive but probably necessary to keep the heat down.

Thanks for your input and stay thirsty my friends!

 

I ended up going Corsa cat back (with valves), as the cost to do sport cats with installation was going to be basically the same price. However, based on your statement:
I'd probably recommend doing the sport cats. The cat back system is LOUD when open. Honestly, bordering on too loud with the top up and rear window down on the HTC, however, it's perfect top down.

 

I have been lucky enough hearing just about every exhaust combo on the C8. I think it depends on what sound you what/like.

If you want a clean pure V8 sound cat back is going to be the move. It keeps the factories smooth tone with just more volume. There are a lot of great options but to keep the valves it is going to be pricey.

If you want a raspier more aggressive tone and volume then HFC are the choice. The cats are more complicated though because the cell count is going to make a big difference in sound. I am installing 200 Cell Stainless Works HFC in 2 weeks and for my ear its the best set up with NPP. More pops, bangs, more aggressive tone but in tour mode its not much louder than the factory track setting. If you plan to do headers and exhaust in the future though a 600 cell cat is the better choice.

Cats you also have to worry about CEL and more potential for denied warranty claims if emissions are tampered with. I am going to run O2 spacers with mini cats but no guarantee's. I live in FL so no vehicle inspections but depending on state this can a be factor. I have no idea the Cali standards for that but I assume it is stricter than Florida....

Can you even modify exhaust at all in CA? I thought anything above 95db was subject to fine?

This is the set up I am going with. Will update once its all installed.

 

Yes, aftermarket cats fail the visual inspection for Calif smog.

But.... with an HTC and your car not needing a smog certificate for 7 years from model year, I am unsure what a smog shop will be doing to pass an HTC.
Ie: Will they raise the roof and remove the solid engine bay cover? Will a windowed cover present a visual failure opportunity?
May have same issue with a Catch Can installation.
Sport cats with a CARB exemption/ certificate is the answer for future no hassle smog testing, but I don't know of any with a CARB.

As for CEL, tone, install ease...YouTube offers many video scenarios.
FWIW I too have an HTC, with NPP & black tips and would also go with the hi flow cat option, leaving the rest of the system as is, with the heat sheilding blankets.

Good luck with your decision, let us know of your success stories.

 

Here a couple good videos comparing although on camera is never as good as in person.

 

Hmm I was wondering about that. They put the car on a lift to check? I have a Z06 HTC and you cannot see anything without raising the car.

 

Sport Cats with OEM NPP is a nice option that will give you more volume and retains the NPP functionality. Quality cats usually won't pop a CEL.

As far as Smog, it's tough to say. The Cats are pretty buried in there so it depends on how invasive the test is.

A catback won't give you any CELs (once the valves are relearned) and is Smog-compliant to my knowledge.

I have a bunch of options in stock (cats & exhaust) and would be happy to discuss!

- Alec
267.788.4897

 

Sport cats win here, but you're in CA so thats a pain, but you don't have to worry for like another 5-7 years... No CEL from them if installed correctly, labor pretty much same cost as exhaust install.

-Josh

 

I have the HTC with budget 2M cats and Hooker Black Heart NPP . All for the same price as one of those super fancy exhausts out there. Heat blanket and 02 spacers included with the cats. Got the MBRP AFM plug to eliminate the system without setting a SEL. Use the metal type oem gaskets or similar.
Sounds super aggressive in Sport then even more so in Track. It sounds like an ev in Tour mode. Good luck with what ever you decide on.

 

Not really sure what your goal is with modifying the exhaust system. If it’s sound then go with a cat-back. If it performance, go with sport cats.

 

I did the Corsa hi-flow cats and changed my air filter to an Afe dry--got performance increase AND much better sound than the stock NPP exhaust. Win-Win!

 

dyno tested before and after ?

 

No but I'd guess about a 7-10 HP bump for the cats and 3-5 HP for the air filter. You can see some stats on the aFe power gains if you want to do a search.

 

I bet you don't even see 5HP with sport cats. When they first came out there were several dynos done on different ones, and many didn't gain anything (or even slightly lost HP), with just a small gain for the best result. You shouldn't count on sport cats or catback gaining any power on C8s, they are really just for sound. With the amount of HP a C8 makes, 5-10HP could be within the variance you're going to see between runs due to conditions/variables.

 

Whatever...I didn't put them on for HP gain, but for better sound.

 

Physics says the minor engine mods (exhaust) increase the horsepower. These gains are small. (<2% of overall hp). Yall are discussing/arguing about measurement errors.

 

We're both in California so we know what a pain and stress it can be getting a modified car to pass a smog test.. The visual is not a problem, especially with an HTC, but the actual OBD test is a concern. I don't think there are any sport cats that are California Air Resources Board(CARB) certified. Also, getting a CEL can be a major pain in the but.

Can you tell me more about "No CEL if installed correctly" ? Also, do you know any shops that can do a Corsa sport cat install. Any shop except American Heritage Performance, that is.
Bottom line, I would do the Corsa sport cats in a heartbeat if they pass smog and no CEL.
p.s. I think the stock black tips look the best! They fit seamlessly.

 

Yes we know a place that will install it. Sometimes people don't tighten them down all the way, so leaks can cause a CEL. Something simple. You have a chance they pass smog since some smog shops don't do visuals, especially if they don't know where to look. But thats all a risk.

-Josh