Catalytic Convertors

[Monki]

In a recent test, I noted that my vehicle (Mazda rx7) would obtain the following under heavy driving

With cat = 220miles on average to a tank
Without cat = 280 miles on average to a tank

And also on past experience, I have noticed that catalytic convertors reduce fuel economy and are therefore "bad for the environment"

the catalytic convertor on the car is in perfect working condition and passed the mot last month no problem.

Has anyone else noticed that catalytic convertors reduce fuel economy? And do you think the government would be interested in banning them on this basis, seeing as C02 emissions per km and bad fuel economy are now worse than stabbing someone


Would be interested to hear their response!

[jammy_basturd]

Didn't the introduction of Cats have more to do with an EU directive than what our nation's government thought?

[LewisR]

Ah, on the face of it, cats are more damaging to the environment than their non-catted counterparts but it is false just to consider CO2 as the only greenhouse gas. Nitrogen Oxides, which are removed by cats, are around 125x more potent as a greenhouse gas. (IIRC, you'll have to check the numbers). I do get your point though, there are some precious metals in cats that are quite energy intensive to remove. I don't think that they solve the problem. Just move it.

[Old Geezer]

Nitrogen Oxide will kill you very quickly!!!

I think what you are saying is that the manufacturer has compromised performance for "Greenness".

[Monki]

LewisR said:

Ah, on the face of it, cats are more damaging to the environment than their non-catted counterparts but it is false just to consider CO2 as the only greenhouse gas.

I've decided to jump on the government bandwagon and use C02 as my only buzz word

[sniff petrol]

I think it must depend on the car as I've taken the cats off my old 325i as I intend to use it solely as a track car and it doesn't seem to have made any difference to the power or economy to be honest - just more noise, but since I got £80 from the scrapyard for my old cats and the car only cost me £300 in the first place I'm still happy.

[dnb]

Removing the cats made a huge difference to my old Scoob. Without cats, I was able to remap the car to run lean-burn on cruise, making arounf 35mpg on a motorway cruise (at least a 5mpg increase). It wasn't too far off passing the MOT either Just a fraction over the CO threshold (0.6% instead of 0.3% from memory - it was over 5 years ago!)

But:

The MOT emissions test is very lax in this country - no test for NOx, and no test done under load, so it's easy enough to get through it with a bit of lateral thinking

And the manufacturers have to offer things like warranties and have much stricter emissions tests to pass - rich is safe and 14.7:1 AFR is where cats work with petrol, not massively lean like I used.

[stuttgartmetal]

Oxides of Nitrogen in gaseous form are poisonous.
Nitric Oxide, NO, and Nitrogen Dioxide NO2 will kill you.
Nitrous Oxide N2O at least will cheer you up, before it kills you.