I think we both know that's Horlicks! When someone says something like that I tend to take everything else they say with a pinch of salt. Probably the wind was behind him or some such.
He wasn’t saying it as a cast iron conclusion just an observation anyway it makes no odds to me my stainless exhaust is set the same way as a stock exhaust
I have fitted a couple of temperature sensors - one in the air coming into the carburettor, and one stuck into the rather smaller aluminium block around the heat risers on a progressive carburettor manifold. Installation : Air cleaner: stock oil bath with stock hot air pickup below tin through "stove pipe". Manifold vacuum operated hot/cold air flap through thermo switch. Exhaust - JK stainless single quiet pack with "balanced" style heat risers which are drilled through to the exhaust pipe (needed doing when I bought it as they are blocked off by default) Carburettor - Weber Progressive with home made adaptor for stock air cleaner installation. Temperature of the air intake, sensor in middle of air flow, above the carburettor - 36 to 46 degrees C (hot day) at idle, a bit less after a while at wide open throttle, as the manifold vacuum drops and the air flap moves to cold. Temperature of the heat riser aluminum block - 85 to 95 degrees C .. not very hot, but the heat riser tubes do get hot enough to smoke oil off them. Overall the heat risers are not too effective, the engine block underneath is hotter than the aluminium section of the manifold. Basically the carburettor drops the temperature of the air as the fuel evaporates, starting off with hotter air helps the vaporisation. I may move the sensors around to measure the temperature of the mixture below the carburettor (bit harder because there are two air paths coming down from the carburettor, mixing when they meet the horizontal part of the manifold.)
Cold air is more dense so carries more oxygen than warm air there’s no denying that. The problem with an engine like the type one that uses a single carb on long intake runners is that the fuel doesn’t stay suspended in the air as a vapour. It separates out so you have air in the runner and a pool of liquid petrol at the bottom of the runner. Liquid petrol does not burn its the petrol vapour that burns. So vw to counteract this added ways of heating the runner This vapourises the liquid petrol which then mixes with the air allowing a more complete and efficient burn of the fuel. Without adding heat to a long inlet manifold with a carb on the end You will get poor running,increased fuel consumption and increased emissions Also the engine will not last as long Carbon deposits will build up quicker and also liquid petrol will wash the oil of the cylinder walls increasing wear as well as slowly thinning the oil and thus not lubricating the bearings as well as it should.
Cheers for sharing it jim You were right I’m a few episodes in on his beetle project and enjoying his realness and calm approach to it all.
The cold air being better for power is why the manifold vacuum operated air flap drops back to cold at wide open throttle and high manifold air pressure / low vacuum. So clever and so often thrown away by going for a simple air filter.
