High Flow Cats - Yes or No?

[Nader]

If you look at Sean Roe's post in the "New Products" forum (see link below), he has come up with a solution for mounting high flow cats. It seems there have been many who have installed high flow cats and continually broke the cats due to engine flex. Sean's design features a flex pipe similar to the stock system.

I have stayed away from high flow cats due the problem mentioned above but now I am reconsidering.

Can anyone give me some insight to what kind of power is expected? I have heard 20hp. Anyone have any dyno runs with a NA set and high flow cats? IN another thread Mark from Woodhouse mentioned that while you do gain 20 plus HP you will lose some torque in the mid range. If that is the case and is proven, then i will stay as is.

My mods to date are Corsa track, KN, DC tune, single blade throttle body.

I am also curious what the change in sound will be. I am running the corsa track which is not too loud. I would like to know if it wil get substantially louder?

Here is a pic of Seans work:

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Here is the thread from New Products:

http://forums.viperclub.org/new-pro...ate-cat-assembly-w-flex-pipe-2003-2006-a.html

Thanks for your help!

Tom

 

[plumcrazy]

while i dont have an SRT, i can tell you on a GTS, taking the cats off DOES make it quite a bit louder but mostly noticed under acceleration. cruising on the highway, it sounds similar

 

[ILLSMOQ]

Those look nice. I don't know about gaining 20 rwhp by switching to 3" high flow cats..you might gain 10. If you lost the cats all together 20-25 rwhp max. You will not loose any torque making the switch...you'll gain some mid range power.

 

[pteam]

Illsmoq,

To lose all the cats do you cut them out and just weld straight pipes in? Do you have any smell / downsides?

 

[Dustman]

That's a GREAT idea and sounds like a nifty product Sean came up with ......... can't wait to hear more details !

 

[ILLSMOQ]

Illsmoq,

To lose all the cats do you cut them out and just weld straight pipes in? Do you have any smell / downsides?

You could do it that way....but when I did it I changed all the piping to 3". Basicly I reused the flange, flex pipe and the hanger. bought some length of 3" aluminized steel and a couple 3" mandrel bends from summit racing. I have a cheap welder from home depot and a sawzall....put them together in a few hours.


As for the smell.....I remember there being a smell the first few days, but I don't notice it anymore....I thnk MikeR had the same experiance with the smell.

It's louder ofcourse but I can't really think of any downsides.

 

[Viper X]

So many of the changes that we make to our cars are highly subjective in nature.

I took the stock cats out and went high flow and it was too loud for me (with headers) - some guys love it.

When I tried running my SRT-10 without cats, it was brutally smelly in heavy traffic, made my eyes water if the wind blew the wrong way - again some guys don't notice it much. I didn't notice it at any kind of speed.

As for hp gains, ILLSMOQU is right, you might get 10 rwhp or so with the high flows. If you eliminate them, maybe 20 rwhp or so. Not worth it in my opinion.

I have found that the high flow cats, being much smaller than the stock cats, tend to clog up easier and don't last as long. The best solution to date has been to buy a set of used OE cats, cut the secondary cat off of the assembly and weld it in the place where you'd install the aftermarket high flow cat. You may find some references to this procedure in the archives.

Th OE cat is cheaper, is much sturdier and a larger diameter than the HF. I haven't done any flow tests (I did this with my Paxton car and it really puts out some serious exhaust flow under boost) but they seem to flow better than the aftermarket "high flow" cats too (someone here may know).

Good luck,

Dan

 

[Nader]

Thanks Viper X. It is interesting that a HF cat does not flow as good a one stock cat in your opinion. Do you think it is due to the diameter? Sean's product is nice since it eliminats all the additional work and you can always bolt the stock system back up if needed. That is a good option for me since I am unsure whether it will be too loud for me. FYI I am not running headers.

Just to note I didnt assume 20rwhp. I assumes 20 total at the crank which still isnt bad. if i can net 10-15rwhp plus and a new, deeper sound, more mid range without the loss of torque and cut back on heat ever further, it sounds like a great mod. I cam always bolt the stock cats back up if it is too loud for me.

So many of the changes that we make to our cars are highly subjective in nature.

I took the stock cats out and went high flow and it was too loud for me (with headers) - some guys love it.

When I tried running my SRT-10 without cats, it was brutally smelly in heavy traffic, made my eyes water if the wind blew the wrong way - again some guys don't notice it much. I didn't notice it at any kind of speed.

As for hp gains, ILLSMOQU is right, you might get 10 rwhp or so with the high flows. If you eliminate them, maybe 20 rwhp or so. Not worth it in my opinion.

I have found that the high flow cats, being much smaller than the stock cats, tend to clog up easier and don't last as long. The best solution to date has been to buy a set of used OE cats, cut the secondary cat off of the assembly and weld it in the place where you'd install the aftermarket high flow cat. You may find some references to this procedure in the archives.

Th OE cat is cheaper, is much sturdier and a larger diameter than the HF. I haven't done any flow tests (I did this with my Paxton car and it really puts out some serious exhaust flow under boost) but they seem to flow better than the aftermarket "high flow" cats too (someone here may know).

Good luck,

Dan

 

[Hiss]

Viper X is right. I believe the stock cats are 4".

A year ago, because it takes less work, I made the mistake of cutting out the secondary stock cat which is metal substrate and left the primary in which is ceramic. Primary did not last but a few thousand miles. The Viper now has no cats. If I had gone with the stock secondary I probably would still have them in the system. The Viper now has no cats.

 

[1fastviper]

Viper X is right. I believe the stock cats are 4".

A year ago, because it takes less work, I made the mistake of cutting out the secondary stock cat which is metal substrate and left the primary in which is ceramic. Primary did not last but a few thousand miles. The Viper now has no cats. If I had gone with the stock secondary I probably would still have them in the system. The Viper now has no cats.

What made them get cloged so quickly?

 

[Dustman]

How "time-consuming" is the installation of Roe's HF Cats ?

Meaning as compared to putting in the the Corsa's which takes hours ?

 

[Hiss]

1fastviper

Maybe because the primary cats were ceramic substrate & not metal. Now the primary cats only was done about the same time the SC was installed and the Viper had about 5500 miles so in 2-3 thous additional miles with the SC the right was clogging up. Never had a problem in the first 5000.

I am not sure on this but I think my SC was tuned a hair on the rich side. So this could(again not for sure) contribute to clogging up the primary only ceramic cats. I think I would rather have the SC tuned a hair to the rich than to much to the lean.

 

[1fastviper]

1fastviper

Maybe because the primary cats were ceramic substrate & not metal. Now the primary cats only was done about the same time the SC was installed and the Viper had about 5500 miles so in 2-3 thous additional miles with the SC the right was clogging up. Never had a problem in the first 5000.

I am not sure on this but I think my SC was tuned a hair on the rich side. So this could(again not for sure) contribute to clogging up the primary only ceramic cats. I think I would rather have the SC tuned a hair to the rich than to much to the lean.

I plan on SC mine someday.So no cats would be the best way to go for me. Im just scared it will be to loud.Do you have any idea about how loud it will be with no cats and corsa mufflers?I mean normal driving is it practical or does it sound like you straight piped it or something?

 

[Hiss]

Cruise speed not loud -pretty good high pitch rumble at idle-wot is loud. I like the sound-little smell at first under long idle but no smell now. Side sills are just warm to touch.

PM me your email address and I will send you a video & sound clip of my Vipers exhaust. I can't get it to work on a VCA post or pm.

 

[Viper X]

Just measured a set of secondary cats that I have in reserve. The OD is 4.5 inches, so inside should be over 4.

Not sure how long they will last in my Paxton car, but when the go, I'll likely hollow them out and run catless for a while.

Sean Roes kit looks clean and it's always nice to be able to undo something that could cause you a smog issue, just can't tell the quality of the cats from the photo.

Dan

 

[plumcrazy]

a tuner i know recently told me he hates all cats and doesnt like them on a s/c'd car. had mine taken right off after that. wont be going back on either. it is a lil loud under acceleration but nice idling and cruising.

if it gets to me, i'll thro another muffler in it. id assume you can do the same on an SRT

 

[1fastviper]

Just measured a set of secondary cats that I have in reserve. The OD is 4.5 inches, so inside should be over 4.

Not sure how long they will last in my Paxton car, but when the go, I'll likely hollow them out and run catless for a while.

Sean Roes kit looks clean and it's always nice to be able to undo something that could cause you a smog issue, just can't tell the quality of the cats from the photo.

Dan

Have they been testedI wonder actually how long those cats would really last?.There not very big.

 

[Nader]

Here is Sean's response in the other forum...

"As far as clogging, these aren't that small, have a very open cell structure (200 cells per inch versus a typical 400 CPI) and are the same style substrate we've been carrying the past two years.
There's no reason for concern at all. Theses are good a quality as stock and are made by an OE level manufacturer. We just lobbied them to make one better "

in this thread...
http://forums.viperclub.org/new-pro...ate-cat-assembly-w-flex-pipe-2003-2006-a.html

 

[Nader]

These are in and I pick up the car tomorrow. I will post my experiences...

Tom

 

[Sean Roe]

Hi Everyone,

I think you guys may be missing why the gain is more than it would typically be with a just a high flow cat. Sorry if I didn’t do a good job of explaining it. Yes, part of it is the deletion of a secondary cat and a single higher flowing (more open cell structure) metal cat substrate, but the rest of it is due to pipe diameter.

The factory manifolds on the Gen3’s use 1.75” primary tubes and exit at 3” collectors, (versus the Gen 1 & 2 at 1.5” primary and 2.5” collector). That makes for some pretty good flow. Inside the stock cat pipe at the flex, the diameter necks down to 2.3”. Ours is a half inch bigger in diameter there and at the bend. That’s a big difference in flow. Moving more air makes more power.

Don’t worry about loosing torque anywhere in the power band. That’s more a function of when you change primary tube diameters on the manifolds, seen especially on Gen2’s when you step up from factory manifolds to 1.75” headers. That looses you a little velocity down low, but makes more HP up high.

Here are some pic links to show you what I’m talking about:

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You must be registered for see images

Regards,
Sean

 

[Nader]

Sean I just came from picking up my car from Tators. First the fit and finish is impressive. Chuck said they went right in without a problem.

As for the sound, man it is mean. Sounds deeper and angryer then the stock cats and corsa. I was getting bored of the stock corsa sound and was looking for something a bit more. This was definitely it. The car definitely is cooler as I was stuck in traffic for 60% of the ride home in 90 degree heat in NY. The footwells were much better and the air conditioning worked better. So far I am very happy the product. After I put some miles on it I will take it to the dyno to see what I am putting down.

Sean do you think I need to reset the computer by unplugging the battery and unplugging the harness?

 

[Kenneth Krieger]

Sorry guys.....just have to jump in here to correct a common misconception about exhuast flow! Bigger is NOT better in the case of exhaust!!! Why? Let's look at the flow of exhaust.....in an internal combustion engine, the A/F explodes and creates a "puff" of air that has to flow from the cylinder to the exhaust port, and out the exhaust tube. Exhaust flows much like water going down a drain.......the gases tend to flow along the outside of the tube, not down the middle......let's use the "nozzle" of a rocket exhaust as an example. Why does the most powerful exhaust have a nozzled "cone" that tapers SMALLER before the rockets spent gases can exit the exhaust? SO IT CAN FLOW "BETTER" , and 'FASTER" and create more thrust! If is wasn't true then the flow experts wouldn't build em that way!!! The exhaust of an internal combustion engine is NO different. Going from a 3" collector and exhaust to a 4" collector and exhaust would make LESS hp and LESS exhaust flow, not the other way around. When you hear "this collector flows better because it's BIGGER, the person, or factory has NO idea of the way exhaust gases flow. Run the other way!!!
In experiments with exhaust, the flow from the head was tested with a larger and larger header tube, and it showed less and less power as the tube got progressively larger.....then the testing was performed by making the opening smaller and smaller, and it's hard to believe but the power was not inhibited even with the opeing down to the size of a quarter. Obviously after that, the flow was too restricted and there was the beginning of power loss.
High flow cats will move MORE exhaust gases in most respects because of this phenomenon. However, there are other factors that come into play, those being the substrait in the cat itself, and the capability of the flow to "hug" the outer portion of the CAT. Did you ever wonder why the CAT was hollow throught the middle? How in the world would it do the job of a cat if the the exhaust gases flowed mainly in the middle of the "tube"? Remember, the majority of the exhaust gases flow along the OUTER portion of the exhaust tube or pipe if you will! Just another thing in the mix to contemplate!

 

[Nader]

These are all interesting points and certainly useful information. You obviously are more knowledgeable about this kind of stuff then myself.

For me, I wasnt looking to put the largest exhaust I could fine. I was looking for cooler sills, better sound and a few more horses. I know that bigger is not better, even with my limited knowledge of engineering etc. When I saw this setup I was impressed. Sean not only improved upon the stock setup, he helped many out there deal with a design flaw with another vendors after market kit. The flex pipe is key to this setup. Recently at dyno run a similar modded car as mine had 32 hp more then me. The only difference he had taken out his cats. This told me there is some power to be had when increasing exhaust flow. Furthermore if this power is developed without loss of torque, I see it as a win, win, win - cooler sills, better sounds and some more ponies.

When Sean Roe comes out with a product I think it is safe to assume that Sean has done his home work and has proven the worthiness a product. From the limited information I know about Roe I do trust that he is putting together parts designed for the Viper to improve upon the performance and original design.

Prior to purchasing these cats there have ben several posts by Sean and others in this regard. There is a lot of detail from Sean on these cats which gave me a comfort level regarding the benefits of this kit. Sean assured me and the rest of us that these cats will build power up top but will not drop torque in the mid range - see above. I trust him on that.

I will be taking my car to the dyno again in a few weeks and will run these against my stock cats. We will see exactly how they perform.

Sorry guys.....just have to jump in here to correct a common misconception about exhuast flow! Bigger is NOT better in the case of exhaust!!! Why? Let's look at the flow of exhaust.....in an internal combustion engine, the A/F explodes and creates a "puff" of air that has to flow from the cylinder to the exhaust port, and out the exhaust tube. Exhaust flows much like water going down a drain.......the gases tend to flow along the outside of the tube, not down the middle......let's use the "nozzle" of a rocket exhaust as an example. Why does the most powerful exhaust have a nozzled "cone" that tapers SMALLER before the rockets spent gases can exit the exhaust? SO IT CAN FLOW "BETTER" , and 'FASTER" and create more thrust! If is wasn't true then the flow experts wouldn't build em that way!!! The exhaust of an internal combustion engine is NO different. Going from a 3" collector and exhaust to a 4" collector and exhaust would make LESS hp and LESS exhaust flow, not the other way around. When you hear "this collector flows better because it's BIGGER, the person, or factory has NO idea of the way exhaust gases flow. Run the other way!!!
In experiments with exhaust, the flow from the head was tested with a larger and larger header tube, and it showed less and less power as the tube got progressively larger.....then the testing was performed by making the opening smaller and smaller, and it's hard to believe but the power was not inhibited even with the opeing down to the size of a quarter. Obviously after that, the flow was too restricted and there was the beginning of power loss.
High flow cats will move MORE exhaust gases in most respects because of this phenomenon. However, there are other factors that come into play, those being the substrait in the cat itself, and the capability of the flow to "hug" the outer portion of the CAT. Did you ever wonder why the CAT was hollow throught the middle? How in the world would it do the job of a cat if the the exhaust gases flowed mainly in the middle of the "tube"? Remember, the majority of the exhaust gases flow along the OUTER portion of the exhaust tube or pipe if you will! Just another thing in the mix to contemplate!

 

[Sean Roe]

Hi Kenneth,
While your comparisons have merit and I won't argue that with you, in this particular case, on a 2003+ Viper, removing the stock pipe and putting on this one (or headers) does in fact make more power.
Not disputing anything you're saying in regard to velocity, but you have to do what you can do on a car where there's no way to alter the diameter of the pipe or nozzle to optimize flow for every operating condition and RPM.
To test these things, shops like mine spend the $30K or more on dynos so we can see if the theory works. The roller weighs the same on every pull and when it says it took X HP to make the roller spin up X fast, it did. Sometime you just have to go with real world results. Since that's the case here and based on your explanation of theory, are we to assume that in the higher flow rates of upper RPM and full throttle that the stock system had a restriction at that point? If not, where else did the additional power come from?

Regards,
Sean

 

[Kenneth Krieger]

Sean........please don't think that I was trying to step on you about this. Every application is different, and I was attempting to get some people educated about exhaust gas flow. The overall concept of changing out the cats is to allow for MORE velocity. That is a given! Having asked many questions from reptable manufacturers of headers (both for Viper and many other applications), the main concensis is that some high flow cats will crack, separate or break because of inherent design. I won't down a product for the sake of making a point, but Random Tech Cats have this tendency. There are others that won't break. It depends on how they are welded, and where the different pieces are welded as to the tendency to fracture. Again, my main point was to educate from my limited knowledge of gas flow rates and my study to have know a bit more about this topic, and pass that on so that others can learn more than they did about flow of gases (in this case exhaust), and clear up some misconceptions. I appreciate your expertise, and what you have learned by trial and error. Again, wasn't trying to be a downer, only maybe a bit of an educator with what I have also learned by trial and error, reading about gas flow research (I know, I'm "different"!!), and it's application to the internal combustion engine!

 

[Nader]

Just wanted to report in. I put roughly 100 miles on the car this weekend. I love the new sound. the car was in stop and go traffic all dave and was cool dispite the 90 degree heat in NY. Feels a bit stronger beginning in the mid to high end.

One thing that is not noted is that these cats should save some weight too. These are definitely lighter than stock. Not sure how much since I didnt weigh them but after putting the stock cats in my pile of used parts I am sure they are.



If anyone is considering these I will be the first to say - do not hesitate.

 

[Hamrhead]

Just wanted to report in. I put roughly 100 miles on the car this weekend. I love the new sound. the car was in stop and go traffic all dave and was cool dispite the 90 degree heat in NY. Feels a bit stronger beginning in the mid to high end.

One thing that is not noted is that these cats should save some weight too. These are definitely lighter than stock. Not sure how much since I didnt weigh them but after putting the stock cats in my pile of used parts I am sure they are.



If anyone is considering these I will be the first to say - do not hesitate.

Could you give us a rough idea of how much you paid to have them installed? Or PM me if you do not wish to post it here.

Thanks.

 

[Nader]

PM Sent a few minutes ago.