gain in power by removing catalytic converter
 

Has anyone tried yet to remove both catalytic converters and replace them with straight metal pipes?
I want to know if the e53 4.4i will still work WITHOUT the catalytic converters and with straight metal pipes instead. I heard there is an increase between 20-30HP only by removing them.
Others say that removing the catalytic converters will cause engine problems and the car will not run at all without them? Is this true or false? The lambda sensors will still be mounted, of course, but inside the metal pipes..

PS I know already about engine emissions problems due to catalytic converters removal, but there are less severe regulations in my country...

Please advise, thank you!

Im sure a few horsepower can be gained, but not 20-30hp, thats a lot!

I dont think its worth it to be honest with you.

Cats out =

- stank exhaust smell
- no hp gain unless you're also changing out the mufflers
- check engine light
- O2 sensor warning
- failed emissions

Even if you went to tubed headers, CAI, straight pipes and race mufflers...you wouldn't get 20 hp. BMW engines just don't do that, they are already built at the top of their game. Changing out the exhaust on a M3 wouldn't yield that, let alone a X5.

Thank you very much for the answer.

However, if the "cat" is defective, removing them still doesn't gain the extra hp I mentioned?
What about the sound? Will it be any different (eg close to 4,6is or 4,8is sound?)
What is the realistic hp gain from removing the cat?

There will be no noticeable gain, maybe 1-2 hp, nothing worth causing check lights. Sound will be barely different as your mufflers are still the same.

DONT do it... the exhaust will smell like hell and if your truck is a light color it will stain the paint(and eat through ur clear).... seen it done (although will have a tougher noise then a stock 4.8 plus a little rattle that i have only heard on porsche)..


the bottom line..

more bad then good.... (do X pipe)

I'd love to see dyno results, I'm betting there's more gain than 1 - 2 hp.

Do you really think the cats are choking down 20 horse? Move up to a bigger cat. Keep in mind, the cat is matched to the exhaust system, so if you are holding back any significant power, it is in the design and diameter of the entire exhaust system, which cannot be blamed on the cat. One good 3" in/out ceramic metal matrix is good for way beyond the horse these motors put out NA. But the pipe on these cars is no where near 3" ID, now is it. ;)

You could probably do a cam and some kind of homemade longtubes, true duals all the way down with an h pipe, and still not outflow the capability of one good quality 3" converter.

If your cat is clogged, then yes it could be dragging some power, but not because it was working properly and holding you back. Cats fail when you have to much raw fuel hitting them, or you do not get them up to operating temp, or both. Has this been happening to you?

It will run with out them, but whats the point? Unless you have a blower or a turbo, you don't need to take the converter off. But if you want to make some carcinogens, go for it.

im pretty sure the sound would be completely different without a cat

In the mustang world we have MIL eliminators for off-road x pipes that eliminate the cats. Essentially they just jump out the connection so the computer thinks everything is working as designed. Not sure if BMWs have something similar.

As for removing cats for performance gains - yes, there are gains to be had. Cats are extremely restrictive. A more environmentally friendly mod may be to find a set of "high-flow" cats that flow better.

IMO the gains don't justify the hassle though. Maybe on a street/strip car, but not on an X5.