You could run them on propane, which doesn't need the catastrophic converters - they make no difference at all if there's no CO or HC in the exhaust stream. Yo

You could run them on propane, which doesn't need the catastrophic converters - they make no difference at all if there's no CO or HC in the exhaust stream. You've got the added bonus that you don't need to strip-mine huge chunks of Africa for precious metals, too.