How bad is the exhaust smell when you go completely catless? I was just about to install a catless downpipe on my F55 when this thought popped in my head. I do school drop off for my kid in the morning, which involves idling in the carpool line for about 10 minutes. I'm wondering how awful of a human I'll be if I subject people to this at carpool. Along the same lines, what if I install the catless DP, but also install a universal high flow cat in the mid section. Are these universal high flow cats effective at all? I don't mind loudness, I don't mind bad smells (within reason), but I'd prefer not to poison people.

 

A well tuned modern engine with a
functioning 3-way catalytic converter
should put out somewhere between
0.05% and 0.5% CO AFTER the converter
has reached nominal operating temp.
Without a converter, it’s more like
3-10%.
Other pollutants like hydrocarbons
and NO2 rise similarly.
Not good (= bad).

 

Thanks for the info. Yeah, when it comes to pollutants, more = bad lol. So at the 3-10% is that a high enough concentration that I'd be poisoning a bunch of kids and their parents if I'm idling or is that low enough that it would dissipate in the atmosphere without anyone really noticing anything?

 

Well, since people weren’t dying
left and right from this before 1974,
... no, they probably won’t die,
but it will smell like a 1970 car exhaust
and won’t score you any points with
the soccer mom Karens.
It also makes it much easier to kill
yourself idling in the garage, and,
as I said before, it’s bad rather than good.

 

I have a "classic" Mini .... it has NO CAT

No one has died in the vicinity of my car .......

plus or minus ONE car is not the issue ....... 99.9% of cars having a CAT' IS the issue ...... and no lead in gas and and and

I'm not a fan of removing emissions control in general .... I can not deny that my Mini has NONE.

 

Oh Lord. OP you are a kind human soul to pose this question, and to be so concerned.

I was born in 1955.

So I chuckle mightily.

God bless.

Cheers,

Charlie

 

Please don't go catless.

It won't kill anyone from a single exposure, it's the cumulative buildup that matters - to people and to the environment. I was grew up in Southern California in the 1960s. I remember days when we had to stay inside at school at recess time because the smog was so bad. (Now it's from wildfires instead of cars.) Your car will smell terrible and the people around you in the carpool lane WILL notice, and eventually someone will call you out on it and you'll be kicked out of the carpool "because your car STINKS and I don't want my kids exposed to that!" Cleaning up our air has been a major factor in improving life expectancy in the US.

There's just no excuse for going catless on a daily driver. Turn your car into a gross polluter for what - a few HP? Even the Subaru boy racers have gotten over that. Get a tune, a bigger intercooler, whatever, just don't remove the biggest advance ever in reducing harmful emissions from internal combustion engines. And don't start with the "but I'm only one car out of millions, and there's lots of cars/truck out there worse than me." It's like voting or wearing masks, we all have to do it, or deal with the consequences.

At least you're thinking about it and asking the question, good on you for that.

 

Yeah, I'm leaning against going catless now, too bad, I already have the DP and its out being ceramic coated. A big part of getting the catless DP was just the costs, $1000 vs $400 is a big jump. I guess I'll have a ceramic coated DP for sale in the market place soon.

 

ya. NO ! . any car i get thats my 1st mod... dont choke my car down and then spew b.s that its beneficial for the engine and car ect. Running catless untuned yea is pretty dumb but when tuned properly and combustion is optimal ect and other smog components are intact , simply removing your cat is JUUUUUUUUUUST fine. Because for every cat us modders remove 3x gas vehicles have been replaced by a hybrid or strait e.v...so CHOP CHOP !

 

I say go cat-less in the down-pipe, leave the factory second cat in the exhaust, and add an aftermarket muffler. That will get you the sound and performance you want for a street car, and the factory second cat will still clean up the exhaust to keep it from being a nuisance.

 

That's like saying "everyone else picks up after their dog so I don't have to pick up after mine." It's not the sidewalks that get fouled, it's the air we all share. Removing the catalytic converter from a street car, tuned or not, is just dumb period, and also a State and Federal crime with serious penalties. There are plenty of ways to get more power without spewing Nitrogen oxides, hydrocarbons, and Carbon Monoxide.

 

After thinking about this a bit, I decided that some facts and science would be appropriate.

First: Catalytic converters are better than 90% efficient at cleaning up the combustion products of an internal combustion engine. Instead of Nitrogen oxides, hydrocarbons, and Cabon Monoxide coming out the tail pipe, you get water, CO2, and N2. If your cat is only 90% efficient, then by removing your cat you are emitting 10x the bad stuff. If it's 95% efficient, then you're emitting 20x. If you want more horsepower, that's easy. You can buy a Mustang, Corvette, or any number of cars with 2x to 3x the power output of a Mini, and that car will pollute LESS than your de-catted Mini.

Second: the claim "when tuned properly and combustion is optimal ect and other smog components are intact , simply removing your cat is JUUUUUUUUUUST fine" is totally and completely wrong. Combustion isn't always optimal, and if you have spent even a few minutes looking at the real time air-fuel ratio or the oxygen sensor output, you'd know that. Every new car sold in the last 25 years has electronic fuel injection, an oxygen sensor, and a catalytic converter. The ECU uses the oxygen sensor to try to keep the AFR the perfect stoichiometric ratio for complete combustion of the fuel, but it can't always do that. One reason is the response time of the engine, especially going off-throttle, all of a sudden there's gas that was sent into the engine to make power that isn't needed. That comes out the exhaust ports as unburned hydrocarbons. Another reason is especially in turbocharged or high compression engines, the ECU will intentionally set the mixture on the rich side at high RPM and high load to prevent a lean condition that can lead to premature detonation and damage the engine. That's more unburned hydrocarbons coming out the exhaust port, the catalytic converter cleans all that up.

Removing the catalytic converter is removing the most important part of the emissions control system on your engine. There's just no valid reason to do it.

 

did you end up selling it?
i have track liimited on mine right now.. so i removed the primary cat. and basically just straight piped mine. i have to say its pretyy badass sound on my 135i. if your into that kind of thing. ohh you must like the small of burnt fuel. its reminds me of a race car now. but mines also tuned to the MHD super licese 91octstage 2plus. so yeahh.