Can catalytic converter reduce performance ?

[SvenG]

Another newbie question.

When we took the Z3 in to have the oxygen sensors replaced the BMW folks told me that it wasn't the sensors that were bad, but the cat 1, one of the two catalytic converters ? That is also what the Carly readout told me; I just assumed the dealer who sold us the car knew what he was talking about when he gave me the two Ox sensors and said that was the problem.

So the question is if the catalytic converter being due for replacement can impact performance. The BMW rep said it can start getting clogged and reducing flow at some point down the road. Here in Florida there are no inspections so that is not a huge immediate concern, but rough running would be.

Thoughts ?

Thanks,



-Sven

 

[Stevo7682]

If the cat breaks up and lodges in the pipe worst case scenario it wouldn't run for more than a few seconds.

 

[hard top]

Yes they do reduce performance and increase fuel consumption, found this out when I decated a Merc.

 

[Stevo7682]

Yes they do reduce performance and increase fuel consumption, found this out when I decated a Merc.

In uk you would not get through an emmisions test without one not many engines run anywhere near clean enough certainly nothing fitted in a z3

 

[t-tony]

There are many cat cleaning fluids out there well worth trying before buying new cats.

Tony.

ps. If you remove the cat(s) to improve performance your fuel consumption is most likely to go up too.

 

[hard top]

In uk you would not get through an emmisions test without one

Put it back on before MOT ....
And then back off again.

 

[hard top]

fuel consumption is most likely to go up too.

Mine went down ....

 

[Pingu]

If you don't need one to be legal and you don't mind killing dolphins, get rid of it.

Restrictions in the exhaust kill power and increase fuel consumption.

 

[Pingu]

ps. If you remove the cat(s) to improve performance your fuel consumption is most likely to go up too.

If you drive hard - yes

If you drive moderately - no

 

[t-tony]

If you drive hard - yes

If you drive moderately - no

That's exactly what I was meaning, extra performance tends to get used until the novelty wears off, sometimes it never does.

Tony.

 

[Redline]

Don’t you have to be wary of losing the cats?
The exhaust will be designed so that the back pressure will form a low pressure area at the exhaust valves. Change the back pressure profile and you can end up reducing power.
Removing the cats may just do that. Yes, you will have a more free flowing exhaust, but, moving that low pressure zone will reduce the scavenging effect as the exhaust valve opens.

 

[Pingu]

Don’t you have to be wary of losing the cats?
The exhaust will be designed so that the back pressure will form a low pressure area at the exhaust valves. Change the back pressure profile and you can end up reducing power.
Removing the cats may just do that. Yes, you will have a more free flowing exhaust, but, moving that low pressure zone will reduce the scavenging effect as the exhaust valve opens.

Back pressure causes a high pressure zone.

I've done a lot of work on this subject and the headers on the M (a supposedly tuned engine) should be around a metre long, but are actually more like half a metre. The collector should be much longer than it is, and the tailpipe is cut to suit the length of the car.

In short, I wouldn't worry about throwing away the restrictive catalytic converter if I could. If anything, the cat probably just confuses the reversion waves into a "mushy noise".

 

[Toby]

I know of plenty of folks that run de-catted cars, for increased performance They just replace the cat for MoT purposes, unless the garage is 'friendly'

Just sayin'

 

[SvenG]

Thanks to all for the discussion and answers.

Interesting.



-Sven