OK, Let me start off by saying that I don't ever condone doing something illegal.

Now that I've said that, "hypothetically", which would be a better set-up: dual hi-flow cats/G92 set-up, or just 1 open straight pipe coming from the header Y-pipe.

I really don't feel like paying for the dual cat set-up if I can avoid it. For the small amount of time I actually drive my car, I won't lose any sleep over not having a functional cat.

 

1 open pipe would be better.

 

That's what I was thinking.

Thanks.

 

I live in the UK and I can legaly run a straight pipe instead of a cat. And that's what I do, it did improve throttle response no end!

Mind you, my cat was very old and probably partially blocked.

 

wait wait, are you intending to keep the y-pipe anyway?

If you're gonna keep the y-pipe, then you should go with dual cats.

The cats(assuming you get high flow) won't slow the movement of the exhaust too much, and it REALLY helps the exhaust get passed the y-pipe because it reduces the amount of exhaust in each pipe before it hits the y-pipe....

which is why the single cat setup was sooo bad, it was AFTER the y-pipe...

which is why that change ALONE made 10 hp increase....

so i say, headers, dual cats, y-pipe, and so on.....or just go with true dual.

dual is cheaper, much cheaper, but if you wanna go for emissions and possibly more hp(depending on the comparing setups), go for the 2 cats.

correct me if I'm totally off what you were asking.

 

As of right now, I don't have ANY of the exhaust system. Obviously, I'm gonna get a cat-back, and I'm gonna run SLP 1 3/4" headers. I had originally planned on adding the dual cat set-up(right now it's single), but was thinking that I could simply run a straight pipe. It would save money not having to buy cats.

...or, I could buy the headers with the dual cat Y-pipe, and just not run cats. That way if I ever decided to add dual cats, I'd already have the Y-pipe.

Basically, the question is which flows better, 2 cats or 1 pipe?

 

Think about it. Either way the exhaust will become 1 single pipe at some point. So why restrict it with cats? The answer is obvious. A straight pipe will be better.

 

yes but the question is when it becomes a straight pipe, which will flow better, more gas or less?

assuming you keep the y-pipe, dual cats will in fact flow better then no cats at all.

If you intend to keep the stock one cat setup, just go with straight pipe, that single cat will only slow you down.

the dual cat will decrease the amount of gas coming INTO the y-pipe, allowing for better, less turbulant flow.

 

lmfao. What are you smoking man?

 

lol

 

Alright. In stock form, the dual cats will infact make more power than the single cat. This is due to the single cat not being able to flow as well as both dual cats. Doesn't matter which you have from the factory, they both "y" down to 1 single pipe. Now if you are going to completely eliminate the cat, like abubaca is wanting to do, you would eliminate any restriction the single car once had. You will also have a smoother transition in the "y" area. I don't have a clue what the guy before was trying to say about there being more gas in the exhaust. It doesn't matter whether you have cats or not, ure still gonna have the same amount of gasses. The cats just convert one form of the gas to a more pollution friendly form of it. You can't just take away gas with a cat. Where does it all go?

 

Car Craft had an exhaust article not too long ago where they tested this philosophy. In the end their conclusion was that by running without a cat you lose a little torque and the hp gain wasn't enough to make it worth running without the cat on a car that came equipped with one.

If I can find the article again I'll scan and post it.

 

that could be true. buts thats a famous magazine, they cant say (they could but they wont) that no cats are better. if having no cat is better for performance why dont race teams run them? why do people with older cars not run them? freeloader - a cat doesnt change the volume of exhaust gases...

 

Yes it does.

The catalyzation process produces heat. Added heat cause the mass to expand. The expansion decreases the density of the mass, requiring more volume to contain the same mass - or, to put it a different way, more flow area to handle the mass flow.

Hence, while it doesn't change the mass of the exhaust, it does change the volume of the mass.

 

if you change the volume of the gas, you can pack it in more, if you can pack it in more, you can have less turbulance when the exhaust hits the y-pipe.

The cataylization(sorry, can't remember how to spell it) burns the excess gas, it DOES make it smaller, just like how when you're exhaust leaves the combustion chamber you have less air leaving then you had going in...it's kinda still there, but not really.

I really wish I could explain it better, I understand why it seems like I have no clue what I'm talkin about.

 

Oh, and about the pro stock cars or whatever...

I'm assuming you're talking about the ones who run headers and thats it.....there's your answer right there.

If you're talking about some branch that uses exhaust pipes, I'm sure they're using rather large true dual pipes, and dual pipes negate the positive affects of a cat.

There's no need to slow down flow and reduce gasses when there's no real backpressure in the first place.

 

The article was based on their Mustang (think its like 86 or 87) which originally came equipped with a cat.

They didn't say to run one or not to run one. What they did say was that the performance gain was not as expected (slight increase in HP, decrease in torque), and for a car that is equipped with a cat, removing it wasn't warranted.