gutting factory cats...

[T-Dubbs]

I'm going to try to gut my midpipes(secondary cats).
They are past the last 02 sensor, so it will not throw a code.
My question
Can I sell the cats in the exhaust?
Do they need them in one piece?
I heard that you could get monies for them somewhere.....

[martin13]

Re: gutting factory cats...

Why bother gutting them? You aren't going to get much of a power increase on a modern car. It might change the exhaust note slightly but I honestly don't see the value. I want to put a cat back in my car. I find the smell annoying and gross

[MechEngg]

Re: gutting factory cats...

You won't gain hardly any power from gutting the cats

[Natty54]

Re: gutting factory cats...

yes you can sell em!

I have a guy who buys cats, wheels and batteries from me to recycle them for me!

[T-Dubbs]

Re: gutting factory cats...

No gains from opening up the exhaust on a boosted car?
Not sure if that's accurate...
Breathing is pretty limited with 2 sets of cats.....

[JPO]

Re: gutting factory cats...

I'd bet on some better flow being, well, better. Just curious why the second set of cats and not the first closest to the engine?

[PRY4SNO]

Re: gutting factory cats...

B5 S4s get good gains from opening them up. I noticed a nice bump in top end and throttle response with my chipped 1.8t A4... Considering the power you're putting down more flow will help now and even more as you crank up the wick.

[R_Ethug]

Re: gutting factory cats...

yes no cats on s4= FUN TIMES.. on a 10 year newer bmw.. maybe not so much? i dunno..

[PRY4SNO]

Re: gutting factory cats...

Got to thinking about this.

Less resistance to flow (aka turbulence) = more cfm = moar power. Or, put another way, less power lost via restriction trying to evacuate the exhaust gasses.

Only thing I can think of that may prove to be an exception to this would be resonance tuning. If BMW engineers designed the exhaust around a specific wavelength gutting the cats could create an imbalance, possibly even reducing output.

[JPO]

Re: gutting factory cats...

Another big plus I've heard for no cats is that the car can move heat out a lot easier. Hot gasses held up by restrictions (cats) = more heat. Also, as I understand it, the closer a restriction is to the manifold the more impactful it is to the car's ability to make power. Im not sure about a turbo car but these are the reasons why, if you have two sets of cats on a NA car, you're better off to get rid of the pre-cats if you are not going full catless.

There's likely a lot of reasons race cars don't run cats.

[Mantis]

Re: gutting factory cats...

Got to thinking about this.

Less resistance to flow (aka turbulence) = more cfm = moar power. Or, put another way, less power lost via restriction trying to evacuate the exhaust gasses.

Only thing I can think of that may prove to be an exception to this would be resonance tuning. If BMW engineers designed the exhaust around a specific wavelength gutting the cats could create an imbalance, possibly even reducing output.

Resonance/evacuation/backpressure/scavenging issue only counts before the turbine, afterwards wide open is best.

Shame on you Martin for stating that no gains will be made, I am willing to bet it improves spool up time, therefore allowing the car to move into a peak powerband earlier

[MechEngg]

Re: gutting factory cats...

Resonance/evacuation/backpressure/scavenging issue only counts before the turbine, afterwards wide open is best.

Shame on you Martin for stating that no gains will be made, I am willing to bet it improves spool up time, therefore allowing the car to move into a peak powerband earlier

On a 1.8t there are hardly any gains from running a cat to going completely catless. That is where this statement came from i believe

[Mantis]

Re: gutting factory cats...

On a 1.8t there are hardly any gains from running a cat to going completely catless. That is where this statement came from i believe

There are always gains to be had, no matter how minimal. Notice that I didn't claim high hp, but perhaps peripheral gains, such as full boost earlier