Cats vs No Cats?
Thread Starter
Cruising
Joined: Oct 2012
Posts: 10
Likes: 0
Cats vs No Cats?
Im installing a set of TSP longtubes on my 2000. The car has all the bolt ons and will be tuned and dynoed after the install. Any pros and cons on keeping or removing the cats? New to the C5 world so any help on the subject will be apprecieated!!! 
Intermediate
Joined: Dec 2011
Posts: 35
Likes: 0
From: Argo Alabama
Just curious did you already get headers or asking for opinions before? I just ordered TSP headers (will be here friday) and did not get cats. I have read mixed reviews on no cats but figured I would give it a shot. Most complaints I hear is the smell but then some say they don't notice it or it isn't bad. Also read where some report that the smell isn't noticeable after a tune. Sorry I don't have actual experience but you should get plenty of answers. I'm curious to hear them too although I already made my decision.
Instructor
Joined: Mar 2006
Posts: 220
Likes: 0
From: ames ia
With out cats....
Car will be a little louder
Exhaust raspier
Exhaust smellier
~3-8 rwhp gain depending on modification level etc. and stock cat vs high flow cat vs no cat
with cats
exhaust doesn't smell
exhaust slightly quieter
exhaust mellows out and slightly deeper
lose a few hp
The cat's are basically like mini resonators in terms of how they affect the sound of the exhaust...
Personally i like a good high flow cat sound wise.... The difference between a high flow cat and no cats is almost non existent in most mid range or stock horsepower cars..
In high HP cars, it can be noticed a tad more, but even then i think its 6 one way 1/2 a dozen the other...
The dyno difference i quoted above was on a 450 rwhp car so if that gives you an idea..
Car will be a little louder
Exhaust raspier
Exhaust smellier
~3-8 rwhp gain depending on modification level etc. and stock cat vs high flow cat vs no cat
with cats
exhaust doesn't smell
exhaust slightly quieter
exhaust mellows out and slightly deeper
lose a few hp
The cat's are basically like mini resonators in terms of how they affect the sound of the exhaust...
Personally i like a good high flow cat sound wise.... The difference between a high flow cat and no cats is almost non existent in most mid range or stock horsepower cars..
In high HP cars, it can be noticed a tad more, but even then i think its 6 one way 1/2 a dozen the other...
The dyno difference i quoted above was on a 450 rwhp car so if that gives you an idea..
Burning Brakes
Joined: Sep 2011
Posts: 764
Likes: 19
From: odessa FL
I knocked out the cats and put in a Corsa X pipe with stock exhaust. Slight smell at first. Loved the sound, the x pipe helped to balance it out. Seat of the pants improved at WOT but I think a lot of that was because one bank was clogged.
It will throw a code unless you tune out the rear O2 sensors or put in simulators.
It will throw a code unless you tune out the rear O2 sensors or put in simulators.
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Drifting
Joined: Feb 2005
Posts: 1,298
Likes: 21
From: east taunton ma
I have LG street series and I choose not to install cats. Deleated the rear o2's and moved them to the front. I had the car tuned. Love the power and the sound. Really, really love the sound. I do have a smell from the exhaust. I have the high flow cats,so if I want I can change out the off road section and add the cats in.
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
In a non FI application, it is important to keep up some back pressure so your exhaust has velocity and proper scavenging. I honestly think that high flow cats are a better idea. Torque is usually more important than hp. For example, when I switched to Borla straight pipes from a Bassani full size muffler exhaust, I gained some hp, but lost some torque due to a loss in back pressure. The cats will have an even more drastic effect.
Safety Car
Joined: Jul 2005
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From: Jackson Tn
St. Jude Donor '06-'07-'08-'09
Race Director
Joined: Apr 2007
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From: South Western Ontario
In a non FI application, it is important to keep up some back pressure so your exhaust has velocity and proper scavenging. I honestly think that high flow cats are a better idea. Torque is usually more important than hp. For example, when I switched to Borla straight pipes from a Bassani full size muffler exhaust, I gained some hp, but lost some torque due to a loss in back pressure. The cats will have an even more drastic effect.
It's a myth perpetuated by people that changed the characteristics of their exhaust piping and then wrongly attributed the power change to the backpressure change.
About the same as that idiotic arguement that your coolant has to flow slowly or it won't cool the engine that just won't die.
Supporting Vendor
Joined: Jan 2013
Posts: 407
Likes: 11
From: Mooresville North Carolina
We prefer cats...keep them on our personal vehicles, and always recommend to customers.
High flow cats do not impede performance by much, maybe 4-7hp on your average n/a car depending on how much power it's making. Even with a good tune, without cats the vehicle will have a stink to it. Also it can make the exhaust sound more raspy, which I'm not a fan of either. Keeping cats also makes state inspections easier (if you live somewhere like we do where they do a visual check).
To each their own, but I always stick with cats when possible
High flow cats do not impede performance by much, maybe 4-7hp on your average n/a car depending on how much power it's making. Even with a good tune, without cats the vehicle will have a stink to it. Also it can make the exhaust sound more raspy, which I'm not a fan of either. Keeping cats also makes state inspections easier (if you live somewhere like we do where they do a visual check).
To each their own, but I always stick with cats when possible
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Melting Slicks
Joined: Jun 2012
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From: Oceanside California
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
Got actual documented proof of this?
It's a myth perpetuated by people that changed the characteristics of their exhaust piping and then wrongly attributed the power change to the backpressure change.
About the same as that idiotic arguement that your coolant has to flow slowly or it won't cool the engine that just won't die.
It's a myth perpetuated by people that changed the characteristics of their exhaust piping and then wrongly attributed the power change to the backpressure change.
About the same as that idiotic arguement that your coolant has to flow slowly or it won't cool the engine that just won't die.
Sorry but you do need restriction to a point on a N/A car.
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
Is that so? So I guess you can just slap the largest possible ported heads on too and not suffer from too much flow and not enough restriction right? The fact that I stated a loss in torque between the two dyno tunes I had, between the two exhausts should serve as some proof.
Sorry but you do need restriction to a point on a N/A car.
Sorry but you do need restriction to a point on a N/A car.
Ummm, port size relates to flow velocity which relates to scavanging. Too big head ports don't cause the engine power to suffer because of too much flow but they might cause the engine power to suffer because of low flow velocity.
In an ideal world, I'd want a port with the proper flow velocity and NO flow restriction. Same with the exhaust. I'd love pipes tuned to match the engine with NO flow restriction. Unfortunately, we don't live in an ideal world and you can't get a properly sized port or header tube with no flow restriction.
Saying a smaller port has more flow restriction so it must be the restriction which makes the head help the engine build low end torque is completely wrong and shows a complete misunderstanding of what is important.
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
Ummm, port size relates to flow velocity which relates to scavanging. Too big head ports don't cause the engine power to suffer because of too much flow but they might cause the engine power to suffer because of low flow velocity.
In an ideal world, I'd want a port with the proper flow velocity and NO flow restriction. Same with the exhaust. I'd love pipes tuned to match the engine with NO flow restriction. Unfortunately, we don't live in an ideal world and you can't get a properly sized port or header tube with no flow restriction.
Saying a smaller port has more flow restriction so it must be the restriction which makes the head help the engine build low end torque is completely wrong and shows a complete misunderstanding of what is important.
In an ideal world, I'd want a port with the proper flow velocity and NO flow restriction. Same with the exhaust. I'd love pipes tuned to match the engine with NO flow restriction. Unfortunately, we don't live in an ideal world and you can't get a properly sized port or header tube with no flow restriction.
Saying a smaller port has more flow restriction so it must be the restriction which makes the head help the engine build low end torque is completely wrong and shows a complete misunderstanding of what is important.
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
Needing flow velocity is not the same as needing back pressure.
