Original exhausts (cat question)

[pepperami]

Been thinking about modern bikes and catalytic converters.

So when you finally have to replace the horrible scabby original exhaust, will the bike be legal if you fit an after-market exhaust that does not have a catalytic converter in them ??

How many modern bikes have a cat in the exhaust system?


The reason I ask is it could possibly affect the choice of the next bike and do the cat`s nick any of the power from a bike? (like a slightly clogged set of pipes)

Just thinking out loud

Plus my bikes are old and don`t suffer that nonsense.
____________________
I am the sum total of my own existence, what went before makes me who I am now!

[Robby]

On some bikes the cat is in the downpipes, some it is in the silencer.

Removing it would violate some manner of law. Being caught for it is another matter. Being successfully prosecuted and losing anything significant is unlikely.

I do wonder about the scenario of the exhaust rotting away, I feel that exhausts are less rot-prone these days. Part of the Euro 4 (or 5 maybe) emissions testing is to prove that bikes can still meet the standard after 20k km (maybe miles). Quick-rot exhaust could be considered as a downside there. A cat has to get hot to work, which means quickly burning off any condensation in the exhaust. This should make an exhaust last longer.

As for losing power, a vehicle with a cat should theoretically be less powerful. In practice, the engine is designed to work with a cat so it's hard to compare like with like. Removing the cat would be unlikely to gain you any power without remapping.

The only example I can think of where a cat robbed power was one of the early MX5s, where the cat model knocked 5-10% off the power output. This strikes me as lazy/quick engineering to meet emissions requirements.

A rambling thread to meet your rambling questions. In short, a cat wouldn't be a reason to avoid buying any particular bike, nor would it be something I would look to remove.

[ZX-7R]

As emissions don't get tested in an MOT i don't see how it is a problem.Only affects manafacturer's selling new bikes,don't matter what we do to them after we buy them.
____________________
Current Bike - 2000 ZX-7R

[Rogerborg]

[stevo as b4]

My old ZX6R had a simple cat fitted at the front end of the silencer. It would have been a simple type like they fit to modern lawnmower engines, as being a carbed bike you don't have 3-way closed loop lambda sensor based fuelling.

The worst offenders for power robbing from having a cat seem to be early 90's cars when the law changed and they had to quickly adopt them in haste as Robby said.

Also modern petrol cars with close coupled cats in crimped together tubular exhaust manifolds look horrendous for flow and exhaust scavenging. I bet a cat free optimised extractor manifold could add at least 10% power, but the Engine management would need re-programming to take advantage.

Manufacturers try to map 14.7:1 air/fuel ratios everywhere they can, until it really hurts performance or drivability, and they go richer then for safety. You can't go lean burn with a cat or it won't work properly, and you can't go rich for performance as it can overheat and damage the cat.

I wasn't aware that current new bikes are not MOT tested for emissions, is there anything in the legislation to say original exhaust system equipment where fitted must stay for MOT requirements?

If not there's no excuse for the poor fueling or rough power delivery on many injected era bikes. Though bikes have seemed to be tuned to need to meet noise limits far more so than cars do, so that will still affect things.

Is all the clean emissions kit fitted more so for the European and US markets though?

[Rogerborg]

[stevo as b4]

It maybe shows how little notice or regard is given to bikes in the UK, and how irrelevant they are seen in terms of any transport strategy the government may have in place. We don't exist, except when there's a toll road pay booth I guess.

[Wafer_Thin_Ham]

[Alex A]

[pepperami]