This subject was raised in numerous threads when discussing adding a header yet it is still unclear to me how one would properly select the "right" Cat for your vehicle based on MODS.

In reviewing many of the threads, I found

1) some saying the stock cat was too small. TRUE?
2) different Cat Model replacement numbers for a Magnaflow (a popular brand choice). I know some called Magnaflow and they advised but what was the basis of their advice?
3) talk that about TOO big of a Cat was bad. TRUE?
4) talk about selecting a Cat designed for a 6 cylinder was the way to choose.

I then went to the summit racing cataloge to take a looksie and it got even more confusing. Let me give you 3 examples -

1) Summit catalytic converters - features 300 holes/inch to deliver 8% less backpressure.

2) Magnaflow catalytic converters - oval version works with up to 375 cubic engines.

3) Dynomax Superconverters have a large body design for up to 460 C.I.D. engines and 26% more frontal area.

So how do you calculate or figure out the right Cat for your car w/ Mods?
Assuming you have what I call level 1 mods (CAI/Pully/Catback) and you decide to add a header and thus need a Cat - which is truely the right size ? Does the selection choice change if you are running a head/cam or a M62 or a twincharge or turbo?

 

I'd love to know this too.

What CAT are you currently using?

 

I am currently running an OBX header with STOCK Cat. I guess you could say that I have been "pro" reusing the Stock Cat because

1) my experience when adding the Header/StockCat to level 1 mods was very positive. I can't claim to have felt a HP gain but clearly a TQ gain. THAT is not to say that I might have gotten MORE from an aftermarket high flow Cat.

2) I am not aware that anyone has had code problems w/ the stock cat.

3) Its a metallic cat not a ceramic.

4) I figured that the car designers allowed for some capacity on the stock cat and that level 1 mods would not exceed that allowance.
PURE conjecture on my part.

Since I started the thread, I went to the magnaflow website and the criteria for Cat selection is vehicle weight ? link - http://www.car-sound.com/04basics/04universal.asp

Which I don't think helps from a MODders selection just replacement.

 

the stock is metalic? i thought it was ceramic. Random technologogies (thunder racing?) and Dynatech seem to have been met with alot of positive results threw the years on this forum. Alot of cats seem to be the same to be almost the same, just different size inlet and outlets. I know that the case with the dynatech anyway. I am going to go with a Dynatech on mine, of coure, thats the only one that will fit that far back (you dont even want to know ) I belive randy webb tested the stocker to 250 hp with no problems, and alot of people with stock cats seem to support that. I would say if your not having problems, and have the stocker on, leave it on. Besides, who to say our cat doesnt flow really well (which i have heard that it does). By the way, magnoflow cats tend to brake down real quick. Been talk of that on this forum, and in alot of other areas of my car world as well. The seem to be cheap for a reason.

WFIW

Beecher

 

by the way, the dynatech is built for drag racing, and its smaller than our stock one (4 inch dia, vs our 6 inch, plus if i remember coreectly, its shorter as well, its 11 inches, and a bunch of that is slip fitting, not sure the actuall length of the cat itself, probably about 8 inches, and even that might be an overstatement, having not seen in the end of one. )

Beecher

 

Ah, but cutting up the stock header is unquestionable for me, as it is for many others.

 

Interesting had not heard that and that would be great news.

I am under the belief that the stocker is metalic - can some one confirm?

I just want to understand the proper way in selecting an aftermarket cat.

 

I'm still using Miltek header/cat...don't know the specs but even though the first two became dismounted due to manufacturing defects, the guys at Stratmosphere have been absolutely stellar in replacing the two headers without hassle

I'm sure I'll be arm twisted into the RMW header eventually when fortune comes my way...although, I'm not sure which cat they use...

Personally, I'm alergic to cats and prefer that they not live under my butt...but...

 

Poor sat on kittys!

 

I also remember someone running a pretty good amount of power(over 200HP) through the stock cat, I just can't recall who it was.

Are you having drivabilty problems? codes? You just want to tinker with something?

I'm not sure you will see any kind of measurable gain by swapping the cat, unless you are going to be making some serious power. Plus it's not something that's easily swapped to test another.

In my opinion, unless it goes bad (breaks up, melts, etc) I would just leave it. If you really want to change it, try to find a welded one.

 

Partsman - My cat is fine - thank you

Unlike MISFITOY, I like being on top of my Kitty .

Anyone remember the Jonny Carson interview of Zaza Gabor? She sits down with a white persian on her lap. During the interview Zaza asks Johnny Carson, "would you like to pet my pusssssiiiieee?" Johnny responds " sure if you move the cat. "

Okay - can we get back on topic - how would you figure out which is the right high flow cat for you MCS?

 

The stock pre cat is metallic and the main cat is ceramic.
I will try the dynatech metallic cat.

Don't forget that people using the stock cat on an obx header may still be using the stock output flange too. I think that would be more of a blockage than the cat itself.

 

thanks for clarifying
Stock output - you mean gasket? pls clarify.

 

I'm still running the stock cat (Hell the guy that installed the cat even decided to use the stock 2.25" piping off the end of the cat and mounted it with my 2.5" exhaust . Probably 2-3 ponies to be had just by opening it up)

Car feels very powerful, only the dyno will tell where i'm truely at for power numbers though . My pre-head dyno was 192 to the wheels with 175 ft. lbs of torque.

 

The piping that comes off the exhaust side of the cat I believe he's talking about.

Many people have cut that flange so that it mates up with 2.5" or even 3.0" exhaust systems with no issues.

 

The 2.25" end of the stock cat and the pre cat itself are my reasons for wanting to add a header.... I just want someone to sell me an OBX that is ready to mount up, without any fabrication on my part necessary.

 

I miss Johnny...Man, I'm glad I'm not getting old by myself...

We were discussing Cats...not Kitties

 

Helix has half of your wish taken care of...scroll all the way down.

http://helix13.com/mini/products/exhaust

 

and keep an eye on the marktplace.

 

You are not alone.

 

Yup, I may be dropping my OBX + Stock Cat for some El D Magic in a few weeks . If I do end up swapping it out, I'll post my OBX with the stock cat in the marketplace.

 

Bart, I have a friend at MagnaFlow, I tried to call her today but she was at lunch. I'll try again tomorrow. We'll see what they say about selecting a proper cat.

 

This is all speculation, so take it fwiw.....

1) Capacity requirments. They will be based on two things. How much air you flow thought the motor, and how rich the car runs. This will tell you how much stuff you have to convert. Too small a cat may not convert everything. But I've never seen anytables that says "Flow, A/F, # cells/SqIn, Cat Diameter" at the top so knowing that our cars run pig ritch and flow like a 3 litre V6 doesn't really help

2) How hot can they go? I got one of the Magnaflow cats and cooked it. I can't say it was the Magnaflow cat, as some mods I'd done had my Exhaust temps really climbing, so it could have been the tune, as much as the cat. But our cars have hot exhaust. Burning happens in the header, and all that extra gas squirted when at WOT has to burn up somewhere. So that leads me to believe that a mettalic is the way to go.

This seems to be a bit of a "market hole" for information. The track only racecars ditch them, and the street driven ones seem to just live with the fact that you choose a vendor and bolt it on.

Before Don hooked me up with a Random for the Stahl system (That is still sitting on a shelf in my garage ), I was looking at something from Davesport, because you can spec the flanges you need on it and the pipe diameters as well.

I'd love it if there was a better way.

Matt

 

not sure what Juston finally used but I think iot is a 200 Magnaflow on the SpiderX

 

How hot is hot?