Well, i think my cat is on its way out on my 535is, car idles a little rough, some loss in power and on top of that, it sounds like i have rocks in there. My question is, should i squeeze my wallet and buy a new cat, or just gut the existing one ? If i gut it, will i turn my car into a 516 (powerwise) ? Have any of you guys experienced a similar situation, and if yes, what did you do ?

Oh, and my other concern is : i just installed a short shift kit which works briliant, but when my mechanic installed it, he said the rubber protector from underneath the shifter (i'm assuming is the one that insulates underneath, not the shift cover rubber) fell apart. I tried realoem and couldn't find a part number. Does anyone know what that thing is called ? Or where to order ?

Thanks

Cat's do a very good job of reducing the nastiest pollutants that our cars put out. Of course I'm sounding like the bleeding heart Californian that I am, but for me, killing the cat is not worth the marginal power increase, given the implications.

Cat's do a very good job of reducing the nastiest pollutants that our cars put out. Of course I'm sounding like the bleeding heart Californian that I am, but for me, killing the cat is not worth the marginal power increase, given the implications.

I'm not looking to increase the power, I'm looking to save some money and asking for opinions in the event I go catless.

I'm not looking to increase the power, I'm looking to save some money and asking for opinions in the event I go catless.

Good for you. Glad I left the Philadelphia area so long ago.

I don't think junkyards are supposed to sell emissions equipment off junked cars, but some might. Look for one that's looks like its in good shape. High flow cats sell on fleabay for pretty cheap, but I don't know how good they are.

If you dont need to pass emissions, get ridda the cat. Its expensive, and a pain in the ass.

If you dont need to pass emissions, get ridda the cat. Its expensive, and a pain in the ass.

Yea, but will I lose power with no cat ?

In my experience, gutting the cat will result in power loss, engine issues with idle and a lower gas mileage. That true ?

It wont be a very noticeable power loss/gain, but keep the cat if you can for world health reasons.

Think of it this way. your m30 motor was built with the intention of a free flowing exhaust. the emissions system was implemented afterwards as to make it US dot legal. so yes your cat is and will rob some power from your m30 motor and it will actually be detrimental to the longivity of the motor. I have a cat on it now. since I put it on, my m30 motor runs hotter and is more slugish compared to before.
gut it, then if you have to go to emissions, spend a couple hundred bucks on another one.
these motors tend to run rich, and that is bad for a cat. It will eventually plug up you cat and blow out your headgasket for increased backpressure. Like mine did on 2 BMW's already.:rolleyes I'm waiting for my emissions test notice now, my car is due. If it wasn't, you'de better be damn certain I'm, gutting it out!! It destroys BMW motors.

heat and backpressure don't go well with aluminum heads on cast iron blocks.

I agree with Bavauto. Gutting the cat. will increase your power, not by much, and will probably give you better gas mileage. And for those who hate polluting the environment, it is actually coming to light that catalytic converters are actually worse for the environment. You are essentially changing one green house gas to another, so how are you helping? The Feds. don't know sh*t when it comes to things like this and don't do their homework.

Sorry, didn't mean to rant.

If you don't have emissions testing, gut it and forget about it. No one will know by looking at it. The other issue you MIGHT have to deal with is "popping" when you let off of the gas as there will be less back pressure in the exhaust system.

...so gutting the cat it is !

Oh, and I've found the answer to my other question. However a new problem arise. I think....my mileage is....very low...like 10 miles to the gallon. Does anyone know why ? No check engine flashing though.

How do you gut a cat? Do you open a seam, remove the guts, and weld it back? Or do you gouge out the inner bits by ramrodding something long and pointy through an inlet?

On the gas mileage issue, you might also consider replacing your O2 sensor. I just replaced mine and the car ('84 633csi) perked up noticeably. It pulls distinctly stronger below 3k rpm. I've only driven about 50 miles with the new sensor so I can't say for sure, but according to the OBC I'm getting better mpg. When an O2 sensor fails, it causes a rich condition, so this makes sense. Also, when I replaced mine, I was NOT getting an O2 sensor light.

cutting a seam , opening it up and gutting it is the best way. As long as its not rusted to death and can be welded.

Thanks guys, I'll just go ahead and empty the cat, the rattling noise is driving me crazy.

How do you gut a cat? Do you open a seam, remove the guts, and weld it back? Or do you gouge out the inner bits by ramrodding something long and pointy through an inlet?

I used a crow bar, punch in and twist into small bits. then shake it out. I cut the pipes off right behind the cat then welding them back up. That was on my e36. the e28 exhaust will be slightly different. Just make sure you have a straight shot with a bar into the cat and bash away.

lots of carcinogens in that material.

lots of carcinogens in that material.

Something tells me that if it buys him 4 hp and saves him a few hundred bucks, "cervi" will be happy to pour the contents into a nearby trout stream.

Something tells me that if it buys him 4 hp and saves him a few hundred bucks, "cervi" will be happy to pour the contents into a nearby trout stream.

How'd you figure that ? Are you a coffee reader ?