Need Cat Converter Opinions

[CROM]

So here is my problem:

I have a Borla exhaust that does not have a 3" inlet, but a 2.5" inlet to accept the stock catalytic converter piping. I would like to get 3" cats, but to do that would require a 3" to 2.5" reducer for each end of the cat. I have been speaking with Jon B and actually placed an order (wife, birthday present) for a set of 3" RT cats but he told me to look into it a little bit more and I came to the conclusion above...aka not going to be easy.

So what would you guys suggest? I have several options as I currently have a custom set of straight pipes installed that are all welded up, I have the stock cats sitting around and I have another set of downpipes with flex pipes lying around I could use. Welding around here aint cheap. I may get headers some day, but not anytime soon. So perhaps I just go with the better flowing than stock 2.5" RT cats for now and try to sell them down the road when I decide to do headers and up it to a 3" cat.

I could:

1). Cut the straight pipes and weld a set of 2.5" cats in and be done (easiest and cheapest) I would like to keep the straight pipes though as they are very nicely made and I could probably get several hundred bucks for them. Completely bolt in pipes from header to resonator for a Viper.
2). Get some reducers and such, cut the straight pipes and weld in reducers and 3" cats
3). Use my other set of downpipes and make a totally new set like option 1 or 2..but that would require more welding and extra SS pipe

 

[chimazo]

I'm not sure I understand your dilemma - why wouldn't you just go with 2.5" cats?

 

[CROM]

3" Cats are high flow and if I ever go to headers I need 3" cats. Im going to have to weld if I use 2.5" cats in anyway, reducers just wouldnt need to be involved. They are both going to be difficult operations, the 2.5" route is just a little easier. I think im going to go 3" cats with reducers on each end welded to the cats and then 3" lengths of 2.5" pipe welded to the reducers and to the header downpipe.

 

[chimazo]

2.5" cats are made in high-flow versions, too, and welding on 2.5" ends to 3" cats will negate any increase over the 2.5" versions you could have bought in the first place.

Do you have a pic of your setup as it is now?

 

[CROM]

I made a pretty picture in MS paint but its on a computer at a different house. My current setup is: Stock headers, stock flex/downpipes with 2.5" straight pipes welded in. I had this set custom made from another set of catalytic converter pipes. Envision a stock catalytic converter pipe with stainless steel 2.5" straight pipe welded in instead of catalytic converters. These pipes then slip fit into the 2.5" Borla pipe that extends out of the Borla resonator, just like the stock resonator does. Unfortunately the Borla end at the resonator is only 2.5", there is no 3" piping to clamp a 3" cat to if I decided to cut the 2.5" piece off the resonator.

I would like to keep the straight pipes as is and not cut them up to weld or clamp in a set of 2.5" catalytic converters. I would like to sell these pieces or keep them. They are very well made and could be a great alternative to someone who does not wish to hack up their 900 dollar stock catalytic converters.

The 3" catalytic converters are "higher flow" according to Jon B. The 2.5" catalytic converters are considered "mid-flow" and if I went that route I would have to upgrade to 3" catalytic converters down the road when I went to aftermarket headers, creating additional cost in the future.

I also have yet another set of stock downpipes/flex pipes that I can use to make a custom set of cat pipes. My goal right now is to get a set of 3" catalytic converters, weld 2.5" to 3" reducers for each end of the 3" catalytic converters, weld extension pieces of piping on to the reducers and weld one end to the downpipe/flex pipe and slip fit the other end into the Borla Resonator.

Most folks that are running 3" catalyic converters with stock headers and an aftermarket exhaust experience half my dillema. They must include a reducer on the headere nd of the catalytic converters. So, all I need to do is put a reducer on the resonator end as well.

 

[Purdue_Boiler_Viper]

Go with the 3". I have used the reducer on RT high flows with no problems. Then, when I did headers, I just removed the reducers. Just make sure you use antiseize to get them apart later.