escape, as the exhaust valve opens, the last remains of carbon monoxide are converted to carbon dioxide in the exhaust manifold (which is partly why they glow bright red when running - but you can't see it as the car is moving!)
Ron Jones It's most impressive if you run the engine without the exhaust manifold - blue flames several inches long and a shattering noise! <Semi-on-topic> The Fleet Air Arm used to fly Walrus amphibians which had radial engines with no exhaust-pipes; one of their nicknames was 'The Flying Gas Ring'. </Semi-on-topic> Sean
