That right there is my question straight up. I have my single cat 85 Iroc, and am crunching some numbers to do the entire exhaust from headers back. The question keep popping up though, both cost wise and flow wise, are 2 cats really better than 1?

Im planning on running alittle over 400HP out of a 383. probably closer to 420 or 430HP by the end of my build in a few years, but i want to do everything right the first time. Whichever option flows better (give or take a few HP) is the one i think i want to go with because i want every little HP i can get. I already plan on getting Dyno Don's headers and one of his pipes either single or dual (thanks for the help don. ill be in touch) but i just cant decide on dual or single. Ive searched the boards and i cant get a definitive answer. Not only that but i'm on a budget and definitly have other places i can spend the $ for a single cat. And then you have more catback (im going 3") options anyways.


so essentially, which flows better. a dual system with 2 decent cats (dynomax? idk whats good here) or a single system with one very good cat (whats very good anyways?). Im looking for a definitive answer!


Thanks guys and im really very sorry if i missed somthing in my search!
~LMSkyliner


edit: wow i messed up that title bad. Any mod that can fix that would you please? If not, then im sorry. IDK how i did that. H isnt even close to D

 

all things equal, 2 high flow cats will flow better than 1 high flow. However there's added expense. 2 high flow cats, plus a good after cat Y pipe like the Flowmaster one.

 

A modern high flow single cat will outperform a factory dual cat setup.

 

Dual cats with modern catalytic converters is the best way to go. You don't want restrictions in your exhaust. Try to minimize them.

 

Im aware of this, however it sounds like dual modern cats will easily outflow a single possibly higher end modern cat. This is kinda what i expected i just wanted to affirm this.


So what kind of cats am i looking for with the duals. 2 magnaflows or 2 Dynomax or ?????? Also, i know some of the catbacks are different because of these. I was really looking into these two: http://www.magnaflow.com/02product/s...merican&id=266

and or one of the hooker setups: http://tiny.cc/6FnuW , http://tiny.cc/62hWH .


will any of those 3 setups support the dual cats? I cant find any mention of it on summit. Ill have to check Jegs.

 

Sure, if you want to pay twice the price for a flow capacity that you don't need.

 

We will find out. We will have a test comming up. Person is now running a single cat and will be going to a dual cat system. We have dyno numbers from the single cat system. The factory did not go to a dual cat system for nothing if there was not a benefit.

The highest flowing catalytic converter I know of flows just shy of 600 cfm. That is not enough in a performance motor. Two of them will flow just under 1200 cfm. That will get it done.

 

this is the kind of info Im really looking for. I only plan on running 450 hp at the motor MAX (550 FT LBS max). However i wanted to do a 150 or maybe even larger shot after that just for kicks and the occasional tough opponent. But ive heard a exhaust at its limits on the engine will severely negate the effects of the nitrous, making it just simply not worth my time. So im hoping for an exhaust system that still has some flow potential left.

 

This is simple arithmatic....the body is the same on the cats. (same dimensions)
Which would you rather have.....8 cylinders forcing it's way thru the one, or 4 cylinders going thru each?
uh, that's a no brainer

 

thats my math but my father continuosly argues that its not worth the money, so i wanted some hard flow numbers to throw back

 

Ok maybe im just not getting this whole dual cat thing but heres were I get confuzed...

you have two headers or manifolds that flow whatever they do ill just say 1200 cfm for example

you can use 1 cat or two we will say the cats can flow 600 cfm a peice

ok thats all good and nice but heres where I start to wonder if it helps...

wether you have two cats or one you still have to merge that into a single exhaust meaning all that flow you gained just got choked off anyway so why even bother?

I could be wrong here and if I am please explain how it helps

btw my old iroc came with the single cat setup and I converted it over to a dual cat setup and didnt notice any difference so if there is one it is not apparent on the street with a stock 350 TPI

 

How big was your tailpipe at the time? How good was the wye in the pipe? I have seen some real bads ones shaped like a T.

By the way I used the term "perfomance motor". You may have gotton a 10hp increase on a stocker and may not have noticed much of a difference. A dyno would be the way to tell or track times.

 

I would think that the dual cat setup would lengthen the manifolds (in theory) making them perform more like itty bitty headers, but if you've got headers already then theyd be a bit redundant unless you were running true duals. Please someone correct me if im wrong.

 

I ran a 3'' flowmaster catback with both y-pipes. I would say screw the dual cat setup. If you are running stock or mild motor use the edelbrock TES and if you have a serious motor full length headers and true 2 1/2'' duals. Both of those things gave me nice gains I could feel

 

If the bodies are the same size, but if you've got room for 2 cats you've got room for one cat that's twice as big.

 

another interesting note after reading what Apeiron wrote is remembering that the dual cat cats are smaller than the single cat

 

Im guessing thats how it might be setup stock? However shouldnt that be false for aftermarket systems? Afterall, i was just planning on using two single cats. I am not aware of any special "dual cat" cat? So wouldnt that mean that the dual cats still take up twice the space?

 

magnaflow sells the y pipe from the headers to the cat as a whole package. Unfortunatley the y pipe *or whatever pipe that u call that goes from the headers to the dual cats* is only 2.25 inches which is what stock is....

 

yea i had already guessed that.


I have a question about that though, what is the difference in length of the I-pipe (i think?? pipe along the drive shaft) from single to dual cat. If i put a single cat system on there, will i be cutting or adding to make it dual cat?

 

I would think shorter one....however I have only run my dual cats so far on my car so far...factory dual cats

 

exhaust is so complex and peopel dont realize it. If your going to build your motor i would wait till the end of your build to do the exhaust. as i understand, with the right amount of back pressure in your system, you can affect the air intake with ur exhaust, but only with the right cam. essentially you can make a four cycle engine (which our small blocks are) into a five stroke motor by forcing the intake to start with the exhaust.what im trying to say is that negative pressure wave can travel through the combustion chamber during the valve overlap phase. which means as the piston travels down the bore (considering your compression is 12:1) your total combustion chamber volume above abnout 730CC will be around 60. the negative pressure will draw out residual gases in the chamber at TDC, and the chamber will be able to pull in that extra 60 CC's. so instead of 730 you will get 790, which basically changes a 350 to abound a 380-385, or at least thats how it will run. Anyways, what im trying to say is that you dont always want to get rid of ALL of your exhaust, because your motor can use it still. its possible to multiply these numbers immensly with proper tuning.

 

I think what you are talking about, is more with "tuned" length, long tube headers. What that does, is they try and make all the primaries they exact same length by using various unnecessary bends. What happens, is, as one pressure wave, or "puff" of exhaust gas shoots out of a certain primary into the collecctor, it creates a slight vacuum on whatever other primary is just about to start the exhaust stroke. This vacuum, can actually help also becuase in a way it "sucks" the piston up some, so the motor has less drag on it from trying to push the exhaust out.

---------------------------------------------------------------

To the origional poster - have you checked out random tech cats? They are supposed to be pretty good in the world of aftermarket ones. I had a catco in my last car blow out in about a year, but I put on about 30,000 miles that year.

Random tech also offers a metal-core cat as an alternative to ceramic. I dont know the advantages or disadvantages of this, maybe somebody else can say. But either way, I think you are better off custom building your own dual cat pipes with 2.5" cats and mandrel bends.
http://www.randomtechnology.com/

Another thing to consider, is, do you have or plan to get Subframe Connectors? Because alot of them wont fit with dual cats.

 

I personaly think the whole dual cat Idea is a big waste of money unless you will be using true duals after them to keep the same flow thru the whole exhaust

 

Or a mufflex 4" would be perfect too. I dont know if 3" would be right for a 450hp motor...

 

What kind of size should i be looking at for about 425 HP + a 150 or 200 shot of nitrous then? 3.5"? 4"?

Also, I simply cant do true duals with these pittsburgh roads unless someone can tell me how to do it without losing a single centimeter of ground clearance.

 

The factory rated the dual cat setup as 10 more horsepower. The manifolds and y-pipe are different, but the cat-back is the same. Believe what you want with that info.

But two 2.5" pipes have the same square inch area as a single 3.5" pipe. So to equal a dual cat 2.5" setup, you need a 3.5" single cat. The single i-pipe works because the exhaust gas cools as it travels out the back.

People are going to argue in favor of what's on their car, because they dont want to be wrong. I have a dual 2.5" cat setup into a 3.5" i-pipe. It works for me. I would recommend a 3.5" setup for 400+ hp with nitrous.

 

Ditto's to what Kevin said.

 

Would two cats make for a quieter exhaust system?

 

383 with nitrous? You gotta have sub frame connectors in my opinion. I have a custom 3" cat delete pipe and had to make custom SFC's just to get past it. And if you can't loose one centemeter of ground clearance then larger than 3" pipe may be a problem too.

I believe that either can perform well. Sure, two will out flow one (of the same flow capacity) and one higher flow cat may out flow two smaller ones... It seems academic at this point. As someone else pointed out, you really won't know what you will ultimatly need until you get it on the dyno and determine if you have a flow restriction. If you're goal is "to get it right the first time" you may end up frustrated. If you need to convince someone else (father) what you need, then it sounds to me you've already made up your mind. The ultimate combination can come only from experimenting with YOUR particular setup. Don't get me wrong, this is the place to get a start and others experiance can be a very valuable guide. Just remember, even with dyno slips from two different exhaust systems it may not apply to your combo unless it's EXACTLY the same.

 

OK. I think im going to go with dual cats from dynomax into a custom Y-pipe from my exhaust guy into a 3" Hooker Super Comp Catback. I just dont want to mess with the 3.5" stuff right now. I just want to drive her
.


however feel free to keep discussing. THeres alot of info here i found very helpful

Thanks
~LMSkyliner

 

they make a single flowthrough cat here in the west i have one on my 88 gta between that and my old car that had the same engine with the slp dual cats the 3 inch aftermarket flowed better you could fell the diffrence and also hear the diffrence the flow through you could shine a light one end and see it out the other it was a street legal true flow through cat i paid 150 for it here in vegas at a exhaust shop but to me a single cat will flow better becuse you arnt cutting it and causing a slight back pressure before the cats then the cats trying to pull the exhaust through them the slaming the 2 channels into one which makes more back pressure back to the exhaust mainfold

 

dual cat engines also got a different cam....