2 1/2" in/out high flow cats? 3" in/out high flow cats?

[DAMN YANKEE]

2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

If one in not, repeat not, going to add headers.
If one is going to add 3" cat backs.
If one is going add high flo cats....

Should one simply go with the smaller diameter 2 1/2" in/out hi-flo cats?
Should one let the cat bcks be the place to move up to 3"?

Is there any benefit for going up to 3" before the cats?

Thanks

 

[plumcrazy]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

never say never on mods...go for the 3"

 

[got one]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

I upgraded to 3" its not too shabby. You will be glad you did.

 

[Camfab]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

If for no other reason than the fact that you may change your mind later, go with the 3" in/out cats. I've done the increase after the cat on the first car, and before the cat on the second car. On the second car, I cut the mid pipe after the sweep and before the cat. I Tig welded a Burns transition (beautiful part) to the mid pipe then welded a V-band to both the 3" end of the transition and the inlet side of the cat. Here's why I did this, I figured if by some chance down the road I decided to put headers on the car, I would already have the proper size cats. The second reason, and I could be way off here but, I figured that gas traveling through the cat gets superheated and naturally expands. My thought is that reducing the outlet side of the cat and then increasing it makes no sense.

I did think about increasing the mid pipe size also, but with the cost of the flexible joints and tubing and additional V-bands I decided not to. As it turns out I just got a "could not pass it up deal", on some prototype stepped headers w/Burns merge collectors. Looks like I made the right choice on the cat size.

 

[ViperJoe]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Are you going with an aftermarket cat-back system?
Most if not all are 3"


I just wished that someone made a short section of 3" elbow that transitioned to 2-1/2" at the factory header connection

 

[DAMN YANKEE]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

All, many thank.
Yes after market 3" are the target for cat backs.
Camfab. Burns transition. I searched and found nothing. I apologize but I do not know what that is. I am guessing that you have provided (along with the V-bands) for a flexible (thermologically) transition joint on the header side of the mid pipe and the header side of the 3" cat. The rear of the cat is pure 3" to 3" cat back. Would you be so kind, perhaps a photo or a link? Sounds like a good solution.

 

[ViperJoe]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

If you are going with a 3" cat back.......3" hi-flow cats are a no-brainer

I have had 3" RT hi-flows and 3" Corsa systems on 2 Vipers

 

[Camfab]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

I know I took pictures, if not, I'll pull the sidesill off Tuesday and shoot a couple of pic's and post them. Merry Christmas, Happy Holidays to all.

 

[FE 065]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Burn's transitions. I just purchased a couple myself a few months ago.

http://www.burnsstainless.com/Transitions/transitions.html



Haven't some tuners just cut off the cat at the front making the entrance to the cat 3" when they added headers? Maybe you could just lop off part of the rear of the OE cat making the exit diameter 3" to mate with your catback.

 

[FE 065]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

I just wished that someone made a short section of 3" elbow that transitioned to 2-1/2" at the factory header connection

Dr Gas has 3"-2.5" reducers. Just make what you want.

http://www.drgas.com/store/product.php?productid=19&cat=14&page=1


So does Summit, made by Dynomax

http://store.summitracing.com/partdetail...mp;autoview=sku


A muffler shop can flare the tubing for OE V-bands

But...that elbow isn't 90deg, it's a bit less.

 

[DAMN YANKEE]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Many thanks, will review. Appreciate it.

 

[DAMN YANKEE]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Ok, I think I have it now. See if this is correct before the questions...

Understanding what Camfab has recommended and think it makes sense...

1. Cutting off the stock catalytic converter.

2. Tig welding on a Burns transition (2 1/2" Inlet from mid pipe to 3" outlet cat side).

First question:

I think I understand the a "V-band" is a clamp the captures a raised/rolled/flaired lip on both mating surfaces. It has stronger holding ability than a typical exhaust clamp and that may be necessary given the heat at the cat. Using a V-Clamp woul keep one from welding on the new cat to the mid pipe and also allows for future use of a header.

If that is true, must I flair a lip on the Burns transition before tig welding it on? The final "bell" on the Burns unit doesn't look like we would have enough shoulder past a new flair to support the V-Clamp on the Burns side?

If that is true, must I flair a lip on the inlet side of the new 3" cat as well?

3. V-Clamp on the Burns to Cat.
4. Clamp on (usual clamps) the cat to cat back.

Is that right? Thanks!

 

[DAMN YANKEE]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Maybe I should be welding the Burns on to the cat and rolling the header edge?

 

[FE 065]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

I'd just use the Dynomax 3"-2.5" reducer. You could clamp that to the OE header pipe end where you cut off the cat. Both ends of that reducer are ID, meaning it'll slip over the OE 2.5" header pipe and a 3"OD cat inlet tube. Unless your aftermarket cat's inlet tube is 3"ID, then you'll have to get a piece of 3"OD to slip into both the reducer and the cat.

Shorten the 2.5" end of the Dynomax reducer to only as wide as your clamp; Accuseal clamps are 1 1/4" wide as I recall. You can get them on ebaY among other places; exact same style clamp that hold the halves of your rear OE exhaust together just after the rear O2 sensor.

The OE header pipe starts its' bend about 1 3/8" forward of the front cat weld, so make your cut as close to the weld as you can to give you the max amount of parallel wall tubing for your clamp to do its' thing. If you don't shorten the 2.5" end of the Dynomax to about 1 1/4" long and try and clamp at the front of it, you'll be trying to clamp onto the OE header pipe as it's curving and won't get a good seal with a clamp.

I've got a slip fit piece over my OE header end now just ahead of where the OE cat was now and it doesn't leak. If you put 2 or 3 slots in the end of the Dynomax reducer the clamp can squeeze down properly. Accuseal recommends you slot whatever tubing the clamp's going on anyway. Don't make the slots longer than 1 1/4" though. About an inch will do. Then mount your clamp right at the forward edge.


Burns sell Vband flanges to weld onto pipes, but they're expensive. They'll make the big end of their transition piece any size you tell them up to the max size indicated on their web page link above. So you could go 3"OD or ID depending on what'd work for you.

I think it'd be easier just to clamp the Dynomax piece on for now. I've seen those 2.5"-3" reducers at the local auto parts place for $2 each.


Take a look at what you've got before you act strictly on MY advice. Though most of October I was under the sidesills fitting up some new stuff, so I think I've got it right..

 

[Camfab]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Sorry, I was busy today, I'll pull that side sill off as soon as I can and get pics for you. You can do the exhaust any way you want as mentioned above. I just tend to be overly anal about stuff I do. I like to maintain things as the factory would do or better. It certainly doesn't mean other methods won't work fine.

 

[Camfab]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Ok, I couldn't wait, so I did some late night work.....

This is a shot of a V-banb connector prior to installation

Here is what my installation looks like

This is a close up of the V-band and the burns transition Tig welded to the high flow cat. It should be clear why I changed over to the high flow cats. Burned insulation at 12k miles. Anyway the V-bands make for quick exhaust removal, since they just pull apart.

 

[DAMN YANKEE]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

First and foremost, many thanks to for all the great information (and clear photos) and all the effort to put it up on this thread. What a resource this place is!

FE 065:

1. What did you cut the cat off with?

2. Is your cat metal or ceramic? How did you go about making that decision?

3. Any special torque numbers on the clamps or is it just intelligently tight?

Camfab:

1. How did you cut your old cat off?

2. Was all the Tig welding done "in place" on the header pipe? What protection measure were taken if it was?

3. What cat am I looking at there? Metal or Ceramic?

Boy did you do a gorgeous job on that Burn's unit! That is one good looking floor!

To both of you:

1. Did you add any special insulation when you put it all back together?

2. Did you use the rivet/head replacement technique on the sills or did the old sheet metal srews work out ok?
I'll get the rig up and the sills off and then make a plan. Will advise and take photos. Thanks again!

 

[ViperJoe]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Comfab, is that a Mopar V-band clamp, and where did you get the flanges for the v-band?

Yank, most use a sawzall to whack the old junk off

The difference in the 2 types of cats at least with RT's is the amount of cfm flow. The more expensive metal substrate flow more and are typically for forced air highly modded cars.

Jon at PartsRack can give you the flow numbers.
Ceramic will do fine for a lightly modded car.

Here's a pic of my welded in RT hi-flow cats

 

[JonB]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

.......Yank, most use a sawzall to whack the old junk off

The difference in the 2 types of cats at least with RT's is the amount of cfm flow. The more expensive metal substrate flow more and are typically for forced air highly modded cars. Jon at PartsRack can give you the flow numbers.
Ceramic will do fine for a lightly modded car.

Yank, there is NO EMAIL in your profile so I cannot reply. Short answer, DONT go 2.5" cats.... use the reducers to achieve flow, coolness, and future expandability.

Despite the references to several vendors above who are NOT sponsors, there are several VCA sponsor-vendors here who offer what you need, and stock it.... In the case of PartsRack, we have probably done over 1000 Vipers as shown above, (thanks Joe)

I hope you will email or call...thank you

 

[22YRSOLD]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

CAMFAB what kind of catz are those.

 

[Camfab]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

First and foremost, many thanks to for all the great information (and clear photos) and all the effort to put it up on this thread. What a resource this place is!

FE 065:

1. What did you cut the cat off with?

2. Is your cat metal or ceramic? How did you go about making that decision?

3. Any special torque numbers on the clamps or is it just intelligently tight?

Camfab:

1. How did you cut your old cat off?

2. Was all the Tig welding done "in place" on the header pipe? What protection measure were taken if it was?

3. What cat am I looking at there? Metal or Ceramic?

Boy did you do a gorgeous job on that Burn's unit! That is one good looking floor!

To both of you:

1. Did you add any special insulation when you put it all back together?

2. Did you use the rivet/head replacement technique on the sills or did the old sheet metal srews work out ok?
I'll get the rig up and the sills off and then make a plan. Will advise and take photos. Thanks again!

1) I marked it in place, then removed the entire assembly off the car. Pulled off factory V-band at header and removed stock cat back. I then cut the cat off using a Porta-Band (hand held band saw).

2) Mock up and tack welding on car, all else done on bench. Make sure the battery is disconnected before doing any welding.

3) Metal substrate

4) No special insulation for now. In time I will use the Inconel heat shields DC Performance sells. They are the best, bar none!

5) I have not had the need to go with Rivnuts, YET! Very little torque + red Locktite for now.

6) V-band assemblies, Solar Flux (used in place of backgassing during welding), transitions, purchased from Burns Stainless. Section of 304 stainless purchased from local distributor.

 

[ILLSMOQ]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Comfab, is that a Mopar V-band clamp, and where did you get the flanges for the v-band?

Burns Stainless v-band kit they will have almost anything else you could want to fabricate your own custom exhaust if your feeling creative and want to use high quality stuff. I'm putting together an exhaust for my car using their Ultra Light race mufflers. Summit racing will also have comparable items for less money SUMMIT RACING v-band kit

Camfab, your set up came out clean .

When I did my 2.5" to 3" transision I used THESE and used a regular flat band clamp ....same result, not as pretty as Camfabs , but you can see the price difference lol.

 

[22YRSOLD]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

CAMFAB WHAT KIND OF CATZ ARE THOSE

 

[Camfab]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

CAMFAB WHAT KIND OF CATZ ARE THOSE

Possibly Bassani or whoever supplies LG

 

[ILLSMOQ]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

I was going to guess Random Techs. . But the weld on the case looks different.

 

[DAMN YANKEE]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

Well gentlemen, how could you ask for anything more on this question? Many thanks for all the kind interest and excellent support. I got all the answers I needed, some great new ideas to ponder and some kind support from John.

Great place for answers....

 

[FE 065]

Re: 2 1/2\" in/out high flow cats? 3\" in/out high flow cats?

First and foremost, many thanks to for all the great information (and clear photos) and all the effort to put it up on this thread. What a resource this place is!

FE 065:

1. What did you cut the cat off with?

2. Is your cat metal or ceramic? How did you go about making that decision?

3. Any special torque numbers on the clamps or is it just intelligently tight?

Camfab:

1. How did you cut your old cat off?

2. Was all the Tig welding done "in place" on the header pipe? What protection measure were taken if it was?

3. What cat am I looking at there? Metal or Ceramic?

Boy did you do a gorgeous job on that Burn's unit! That is one good looking floor!

To both of you:

1. Did you add any special insulation when you put it all back together?

2. Did you use the rivet/head replacement technique on the sills or did the old sheet metal srews work out ok?
I'll get the rig up and the sills off and then make a plan. Will advise and take photos. Thanks again!

I just use a hack saw...

I don't have any cats at all(!) Easy decision

I think they recommend 55 ft/lbs torque for the clamps. I've read since that you shouldn't torque clamps when HOT..must be why I found some hard to get loose again when taking it apart again.

I did the rivet nut conversion late last Summer. I don't know if I ever stripped any of the OE sheet metal screws or not in 10yrs of various Vipers,..I've lost a couple off the bottom of the sills though now and then.