how many heads and cam or 9 liters engines running decat pipe rather than sports cat

[stradman]

Just out of interest really. wanted to know and hear consensus, reasoning as to why, either way. I'm currently running sports cat on my 9 L but considering the alternative.
Cheers

[GTSilver]

I've been running catless since I got my h/c package back at the end of 2015. Reason behind is it to reduce heat, weight, a bit of power and an intoxicating sound as we dont have noise limits in the race tracks that are close by.

[Arizona Vipers]

Just out of interest really. wanted to know and hear consensus, reasoning as to why, either way. I'm currently running sports cat on my 9 L but considering the alternative.
Cheers

Why are you asking? You are running cats right? Can you ditch them in Europe? I'd have to guess on your motor it's worth 12-15hp

[Jack B]

Look for a Prefix thread, all cats are not equal, some can cost substantial hp.

[stradman]

Why are you asking? You are running cats right? Can you ditch them in Europe? I'd have to guess on your motor it's worth 12-15hp

Well had a slight problem with failed cat on one side so considering options that's all. Worried about comments I hear from people that say smell is intolerable. Tbh even with the sports cat I can smell the fumes of unburnt gas anyway to a degree. Not sure how much worse it would be as with these engines all the sensors are deleted anyway. So interested in comments that's all. I probably couldn't pass the emissions test anyway even with the sports cat so unlikely removing it will change things on that front.

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Look for a Prefix thread, all cats are not equal, some can cost substantial hp.

Yes had the Prefix cat installed.

[Vipes]

Look for a Prefix thread, all cats are not equal, some can cost substantial hp.

Agreed. I'm currently running 200 cell metallic substrate high flow cats (ARH full system). The car is getting heads/cam in the next week or two so I considered catless but decided to stick with the HFC. Mostly a personal preference decision. I had a cat delete H/C gen 3 and it was awesome at first but after a while the smell and ear piercing sound/drone got old, or maybe that's how I know I'm getting old. It's worth the 10-15 hp hit to me, decided to get the lost power back by doing all the other small mods.

[IHOP]

Well had a slight problem with failed cat on one side so considering options that's all. Worried about comments I hear from people that say smell is intolerable. Tbh even with the sports cat I can smell the fumes of unburnt gas anyway to a degree. Not sure how much worse it would be as with these engines all the sensors are deleted anyway. So interested in comments that's all. I probably couldn't pass the emissions test anyway even with the sports cat so unlikely removing it will change things on that front.

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Me too on the smell, I have the ceramic cats Belanger sells (not sure who really makes them) and I can smell fuel on cold starts.

[Whitey]

I run both. (ARH high flows and stock catback; 3 inch straight pipes). Scot at Prefix contributed to a thread showing their dyno results (20hp loss using high flow cats) I put on the straight pipes for runway events when volume isnt a concern. Your 9LX motor with straight pipes will be amazing!

[RedTanRT/10]

Just out of interest really. wanted to know and hear consensus, reasoning as to why, either way. I'm currently running sports cat on my 9 L but considering the alternative.
Cheers

Stradman, I think you are just using your viper for track events. Other than the sound restrictions you've spoken about in the UK, there's no good reason to run with cats in a race car.

The up side is more HP and cooler side sills, (and no way to burn up the cats), only real downside is more outside noise and cabin noise. The interior sound level on my ACR and CC was certainly louder, I was using ear plugs but made the switch to a Stilo helmet with earmuffs and I don't need ear plugs anymore.

Folks that speak of smell are more likely experiencing that off-track. I've got a really sensitive sinus and I can smell it occasionally at start up or going to the grid. But the smell of brakes and clutch is definitely worse! Best wishes and good luck!! Mike

[TrackAire]

I run totally catless.....cold start ups are going to be stinky with or without a cat until they fire off and even then, I rarely just sit in a Viper at idle with the windows open.

What I've noticed is I can smell the other cars when on the track since they are at wide open throttle so much....even with cats installed WOT is going to get stinky if you catch up to two or three cars trying to stay in front of you. Lots of hydrocarbons getting dumped out the exhaust under high loads and rpms.

[Arizona Vipers]

Well had a slight problem with failed cat on one side so considering options that's all. Worried about comments I hear from people that say smell is intolerable. Tbh even with the sports cat I can smell the fumes of unburnt gas anyway to a degree. Not sure how much worse it would be as with these engines all the sensors are deleted anyway. So interested in comments that's all. I probably couldn't pass the emissions test anyway even with the sports cat so unlikely removing it will change things on that front.

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Yes had the Prefix cat installed.

Here in AZ our emissions are pretty tough and all my Viper's have passed with no cats (since they are in the side sills you can get away with the visual part of the inspection obviously).
I don't notice the smell, but maybe I just got used to it. I always run 101 unleaded, will be running higher octane soon, not sure if that will make it worse or better.

[stradman]

Stradman, I think you are just using your viper for track events. Other than the sound restrictions you've spoken about in the UK, there's no good reason to run with cats in a race car.

The up side is more HP and cooler side sills, (and no way to burn up the cats), only real downside is more outside noise and cabin noise. The interior sound level on my ACR and CC was certainly louder, I was using ear plugs but made the switch to a Stilo helmet with earmuffs and I don't need ear plugs anymore.

Folks that speak of smell are more likely experiencing that off-track. I've got a really sensitive sinus and I can smell it occasionally at start up or going to the grid. But the smell of brakes and clutch is definitely worse! Best wishes and good luck!! Mike


I run totally catless.....cold start ups are going to be stinky with or without a cat until they fire off and even then, I rarely just sit in a Viper at idle with the windows open.

What I've noticed is I can smell the other cars when on the track since they are at wide open throttle so much....even with cats installed WOT is going to get stinky if you catch up to two or three cars trying to stay in front of you. Lots of hydrocarbons getting dumped out the exhaust under high loads and rpms.


Here in AZ our emissions are pretty tough and all my Viper's have passed with no cats (since they are in the side sills you can get away with the visual part of the inspection obviously).
I don't notice the smell, but maybe I just got used to it. I always run 101 unleaded, will be running higher octane soon, not sure if that will make it worse or better.

Thanks guys. In the end at least initially I will be running decat, getting a small muffler in the space of the cat-which in fact will be freer flowing than the cat but at the same time will act as another expansion chamber to help with sound levels. It will defo run cooler this way and probably release a couple of horses. I'll then see how I get on with smells etc after that.

[Arizona Vipers]

Thanks guys. In the end at least initially I will be running decat, getting a small muffler in the space of the cat-which in fact will be freer flowing than the cat but at the same time will act as another expansion chamber to help with sound levels. It will defo run cooler this way and probably release a couple of horses. I'll then see how I get on with smells etc after that.

it's gonna be a lot louder too..... My car is always the loudest car at the track and I'm running mufflers!

[stradman]

it's gonna be a lot louder too..... My car is always the loudest car at the track and I'm running mufflers!
Well I'm running a custom muffler which is much quieter than the OEM muffler and when I remove the cat, in its place will go a similarily designed smaller muffler so should not be that much louder...These are proper mufflers that actually silence noise. The OEMs are actually almost straight pipes I'm afraid...

[Topplayer]

Well I'm running a custom muffler which is much quieter than the OEM muffler and when I remove the cat, in its place will go a similarily designed smaller muffler so should not be that much louder...These are proper mufflers that actually silence noise. The OEMs are actually almost straight pipes I'm afraid...

did you post any info on this? I find that idea interesting

[dewilmoth]

Well I'm running a custom muffler which is much quieter than the OEM muffler and when I remove the cat, in its place will go a similarily designed smaller muffler so should not be that much louder...These are proper mufflers that actually silence noise. The OEMs are actually almost straight pipes I'm afraid...

Your exhaust is a work of art. Love the idea of big power without obnoxious sound levels. I guess I’m getting old. When I eventually build my motor, I’m going to have to find someone to do an exhaust like yours, but finding that kind of quality is always tough.

[stradman]

Your exhaust is a work of art. Love the idea of big power without obnoxious sound levels. I guess I’m getting old. When I eventually build my motor, I’m going to have to find someone to do an exhaust like yours, but finding that kind of quality is always tough.

Scot at Prefix can now help. He got an identical one to mine shipped over to him for a customer, once I gave him the contact details, so he can defo do it! He was also quite impressed from what he told me when he heard it on the customer car....

[dewilmoth]

Scot at Prefix can now help. He got an identical one to mine shipped over to him for a customer, once I gave him the contact details, so he can defo do it! He was also quite impressed from what he told me when he heard it on the customer car....

Nice!