Hey guys,
I'll be ordering some TPiS longtubes here shortly, and I'm looking to get some high flow cats. Excluding Random Tech cats (they're too expensive), what would be a nice set of high flow cats that are relatively inexpensive?
I've been looking at these:
http://www.car-sound.com/02product/d...versal=99959HM
http://www.car-sound.com/02product/d...niversal=59559
Also, I have a few questions about cats in general...
1. If the cats don't have a prefabricated O2 sensor bung, what should I do?
2. Is ceramic or metallic better?
3. Does case sizing make a huge difference?

 

Those should be fine.

Install bung

Ceramic

No

 

Why is ceramic better?

 

Try to get high-flow cats... They will help out performance wise

 

Lol, that's what the whole point of the thread was, which set of high flow cats I should get...

 

If i cant run duels ill have an extra Melrose cat forsale.
Ill let you know!

 

Well, unless I missed something those cats in your links are not high flow... They are regular bullet cats...

 

I'm looking for 2, but thanks haha

 

Those might run you as much as RT cats. I saw a link for $198/pr recently. Those Magnaflows are probably similar price. Either would work fine and flow better than stock.

I think case sizing can make a little difference because the larger cased cats have more surface area to get fumes thru. Not a HUGE difference though.

 

Thanks for the input! Lemme ask you, if you were in the market for a decently priced high flow cat, which would you go with?

 

My understanding is metallic cats are "better" if your goal is performance. But not if your goal is clean emissions. I wish I'd gotten a picture of mine, but I believe the matrix is not as dense, so they can flow more. But of course that means the exhaust is not in contact with as much catalyzing surface.

With longtubes, will that first one you linked up even fit? It looks pretty wide, longtubes put the cats quite low.

 

The one that best suited the application. I might use a spun cat that's got a 45-degree angle on one end to help the tight transition where it curves into the belly.

By contrast, it sounds like you need/prefer one that's got a bung. Though I THOUGHT the bung-equipped model looked kinda big (like Aurora), reading the measurements make it look like they might be the same case diameter.

For people not needing a bung or special fit, Random Tech seems to be the popular choice. I believe they are more touted for better flow. Plus, it looks like I posted the price backwards. The link I saw was $189. Since you're using two of them, the HP results shouldn't be THAT different depending on which one you pick.

Keep in mind racers wanting the best trap times would NEVER consider installing cats in the first place. The best flow is withouth one. According to the Flowmaster tech that's a forum member, he thought front cats disrupted some of the scavenging effect. But, he also liked front cats better than a center cat because (in his words) higher velocity at the collector would help "blast" the charges thru the converter. After talking to him, it sounded like the best cat was no cat! Hence, racers don't use them.

One final note, he call cats one of the better mufflers though. They'll quiet better than wide-open glass-pack/resonator styles -- but flow better than chambered muffers. Since they "clean" and muffle, I like them as a one-step solution where space is a problem. Buying one part vs two (muffers and cats) has it's appeal too.

 

High Flow Cats:

 

I suspect also there is a safety reason. Cats work by turning unburned hydrocarbons into mainly heat and CO2, and H2O.

On a race car, you are spending large proportions of time at WOT, where the engine is intentionally running rich. The cat has to deal with all that extra fuel by turning it into heat, and could probably melt down or catch fire.

 

I'm aware that having no cat at all is the best for flow, but I want to pass emissions lol. Don't I need a cat with a bung? Do most of you tune out one of the O2 sensors or something?

 

I got the Dynatech cats when I bought my TPIS. They were around 169.00 each though. One thing I'd recommend, don't get cats with a dia./width any larger than 4". That's what I have and they are plenty close enough to the under body.

The one on the left came off my old SW system.

 

You could always add a bung in the pipe past the cat if you wanted. You don't have to limit your choices to ones with one already. But does your 94 need a post-cat bung?

 

bungs on mine are before the cat (when I still had cats). Do a search on ceramic substrates and I think you find the metal screens a better choice. I got a set of slightly used RT's if you're interested.

 

Well with the help of a forum member , I was able to find a site selling RT's for $169 new, so I'm gonna go that route

Another question, would it be advisable to get 2.75" cats since that's the size of my exhaust or 3" cats since that's the size of the TPiS collector?

 

It would be better if the header collector went inside the cat. If it's 3" out though that's where the problem comes in. I'm going through this now with mine mainly because I want to be able to separate the header from the exhaust. You could have it all welded up then just cut it if and when you need to remove the headers. Or you could go to a muffler shop and have some pipes sized to fit . Good luck