cat Killing

bulachip · 10-20-2004, 08:36 AM

Is it true that one gains more significantly more power and gas MPG from removing their CAT? are there any negative repercussions? How is this done? Do folks recommend it?

Rmills944 · 10-20-2004, 09:01 AM

I thought the thread was about something else. I guess I'll answer it while I'm here though.

Without the cat, it's hard to pass emisssions. The performance gains are extremely good though. One thing you can do is to get a test pipe with a cat. This way you can just bolt in the cat when you need it to pass emissions, then remove for driving. The cat is a slip on cat for the test pipe and just bolts on. Speedforce racing makes such a cat, but it's not on the catalog yet. The cat adn test pipe run $599. I've looked into this before too...

mambodave · 10-20-2004, 09:07 AM

I have a Bursche Cat bypass pipe you can have for $100. Its for early cars.

NKN84944 · 10-20-2004, 09:09 AM

Dave, is the bypass pipe essentially a dump?

mambodave · 10-20-2004, 09:15 AM

Im not sure...Ive not used it. I bought it...but then i sold the 944's
The section on the pipe replaces the old section where the cat is, if im not mistaken. But im not sure since I really never looked into putting it on.

I think it will pass a visual inspection:

bulachip · 10-20-2004, 10:16 AM

how much of a preformance gain are we talking? Is it worth the trouble?

mambodave · 10-20-2004, 10:58 AM

I have absolutly no idea.. my best guess would be 20 hp or less???

Maybe someone who has done it can chime in?

Macfreak007 · 10-20-2004, 11:28 AM

expect to see maybe, possibly 1-2 hp out of a test pipe, these cars actually do better with a little more back pressure, which the testpipe provides. if you want a different sound just get a different muffler. You will loose some low end grunt, but gain a little high end with the test pipe.

NKN84944 · 10-20-2004, 11:32 AM

Oh, ok it is definately not what i was thinking. I always wanted to try welding a dump onto the existing downpipe with a manual lever for the valve. I have a few friends who did that with good results on mustangs, but I am not sure if it is legal or not or how well it works on our cars.

Zero10 · 10-20-2004, 12:14 PM

It's just not worth the trouble to try and gain the 1-2HP. It's not worth the environmental damage, for a performance gain you can't feel.

On the other side of this argument, does anybody know a cheap place to get a catalytic converter? I seem to have a test pipe, and my conscience has finally caught up to me. Besides, the muffler is going anyways, so I will probably just replace the whole exhaust after the headers.

bluebullet · 02:37 PM

ive had nothin but good things to say about removin the cat. Yeah it is kinda hard on the environment...but compare you car...to all those diesel trucks that belch black smoke and all those POS beater cars that smoke oil and crap. A clean running Porsche will hardly do things (yeah yeah Im gonna get flamed....help save the environment one car at a time)

I dont have a cat, and to be honest, I might have lost some low end torque, but its a 2.5L...I didnt feel anything. The top end however, with a good set of headers, you will see some nice gains because the car just keeps pulling hard. I would estimate in the 8-10hp range. Especially if you have the stock cat which is now almost 20 years old. Turbo cars that I work on and/or build have no cats unless the customer specifies. I have seen cars knock due to the addition of a cat, and lose up to 50hp or more. Plus its an exhaust restriction, that keeps EGTs high and keeps combustion chambers on the hot side, maybe to the point of melting things.

Also, that tale of 'N/A cars need some backpressure' is straight BS. No car needs backpressure. That is pressure that is working against the motor thats trying to pump it out of the cylinder. What you need is a high flowing straight through exhaust.

At this point, people will start to argue because 'oh well i put a full exhaust on my car and my car feels dumb slow now on the bottom end'. Well that is due to either:

1. You own a honda
2. Your exhaust piping diameter is too big for your motor.

Constantly I see mass manufactured exhaust systems for hondas and other import cars that are smaller than 2 liters. They give you a 2.5inch exhaust, and that is way too big. the exhaust comes screaming out of the port and just slows to a halt because the pipe is so huge. And what is easier to do? Expand right there or try to move down the pipe? The exhaust will expand to fill the pipe, and the result is that all that energy that was supposed to keep it moving now was used to fill the pipe, and it slows down. Now the cylinder has no scavenging effect, and the exhaust has to get pushed out of the cylinder, instead of partly being 'sucked out' by the scavenging effect. This principle is what makes or breaks a set of headers. One wrong bend or bringing two cylinders together at the wrong point on the header can turn a well performing header into a piece of crap.

The idea is to have a small pipe diameter with a free flowing muffler. This creates a high exhaust velocity, and helps scavenge exhaust from adjoining cylinders. The higher you can get that exhaust velocity, the more of 'sucking effect' you can get when the next valve in sequence opens up. That means less effort to get the exhaust gases out, and that means more hp to turn that crank and put the power to the wheels.

Magnaflow would be my best muffler to use, because it is straight-through and offers a lot of fiberglass packing to quiet it down. It also doesnt have those louvers that stick out into the pipe like those cheap cherry bomb or glass packed mufflers have. A full 2.5inch exhaust system (our 2.5L is quite big and the bore size is up there, which will equate to a lot of exhaust flow) or maybe even just a 2.25 exhaust system, with a magnaflow resonator in the middle to keep things quiet, and a mangaflow muffler in the rear. Using all mandrel bends, and keeping the straightest line possible to the back of the car, and you will truely have an exhaust that doesnt sacrifice any low end power and give you good gains up top...all the while keeping it quiet and non-ricey.

Rmills944 · 10-21-2004, 05:33 AM

I have a magnaflow on there now, and I'm getting ready to get rid of it. I'm going with Speedforce Racing's cat-back. This system uses 2.5" and a stainless pipe all the way back with a Borla muffler. It sounds much deeper than the Magnaflow (my only complaint about it) and Borla flows about as good as Magnaflow on the tests I've seen on Mustang Dynos. Seeing that my pipe needs replaced, I figured I'd just get the SFR system though.

bluebullet · 10-21-2004, 08:55 AM

I have a borla sportsman xr-1 muffler that was going to go on the colt, but current redesigns and the change over to a full track car now have me going with a 10" magnaflow that is going to fit between the frame and my front bumper, allowing for a front bumper, side exit exhaust that is still legal at the track...