Catalytic Converters and Carburettors

[Tintin]

There have been some interesting discussions about the latest London Low Emission Zone requirements which set me thinking. Is it practical to fit effective catalytic converters in the exhaust system of a carburetted XK engine? My objective is not to save the planet from pollution, but to clean up the fumes and smell from my tailpipe emissions so that the boot of the car doesn't become so sooty between car washes and the inevitable proportion of un-burnt fuel is reduced.

I don't understand the chemistry of it all, but understand the difficulty may be controlling the fuel/air ratio to make the converter work effectively - if success means fitting O2 sensors and air injection I think I'll give it a miss.

Has anyone tried this?

Robbie

[mike020150]

Some US series 2 carburetted XJs were fitted with catalysts but the same cars also came as part of an emissions package including air pumps and other power and mpg sapping devices. On carburettor cars, the catalytic converter was fitted in the first intermediate pipe. However, I suspect that being that far away from the exhaust manifold, a lot of the time the converter ran too cool to be terribly effective. Series 3 (fuel injected) cars had a more usual set-up with the converter being sited in a hotter/more effective position in the front down pipe.

If your car is suffering from a sooty bum, is it possible it's simply running an over-rich mixture or weak ignition (high speed misfiring), requiring adjustment or similar attention? Mike.

[Tintin]

Thanks, Mike. I was afraid it wouldn't be a straightforward retro-fit. The plugs are a good colour, so I don't think its running over-rich - probably just me being fussy.

I have heard good (but not universally good) reports on the 1-2-3 electronic ignition system for these engines, but mine already has a breaker-less conversion and I'm not sure if the 1-2-3 system would give a worthwhile improvement over that. Its had a new coil and ballast resistor, the dynamic timing is OK and the plugs leads and distributor cap are all recent, so I'm not expecting a weak ignition issue. Is there a way to test for that?

Robbie

[mike020150]

It sounds a bit like you might be expecting the old girl to behave younger than her years. If she's capable of exceeding 20mpg on a run, there's probably not too much wrong with her. Emission standards were so much looser in those days. A few unburnt hydrocarbons were perfectly acceptable then. As a hobby car clocking up relatively few miles, enjoy her for what she was designed to be rather than spending money for marginal improvements to her emissions. Next year will be a big one for XJs (the 50th anniversary). My advice is to get out the polishing rags and apply some old fashioned elbow grease so she looks good for the celebrations! Mike.

[Tintin]

Yes you are of course quite right, Mike.

I'm getting just over 17mpg overall, which I thought wasn't bad with the gearing of the three speed automatic box (relatively high rpm for a given road speed).

Looking forward very much to next years events!

Robbie