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a 28 carb will flow exactly the same volume of air as a 28mm copper pipe, as basic physics means with all things equal you cannot push or pull more air through the same size orifice...
(obviously there are slight variations .. Polishing, smooth openings etc etc... but then things would not be equal!)
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But won't pressure difference between the 2 ends of the pipe/carb barrel affect the maximum flow rate?
In terms of how much air is drawn into an engine per revolution:-
On a naturally aspirated engine you're looking at the number of pistons moving downwards on the intake stroke per revolution (not the engine displacement!), which is then reduced by the volumetric efficiency of this engine - basically, due to various restrictions, port size, fluid friction, time lag/inertia of the fluid (air), throttle restriction etc., no engine draws in 100% of it's cylinder capacity, the real world figure might be say, max. 90% efficient. When people enlarge/smooth ports, fit larger valves etc, they're trying to improve the volumetric efficiency of their engine. Improving the V.E. means more air is drawn in, and therefore a corresponding increase of fuel can be drawn in and more power results (hopefully).
On a 'blown' i.e. turbocharged or supercharged engine, the air is pressurised by the turbo (driven by exhaust gases) or the supercharger (driven by the engine but there's some modern electrically driven ones nowadays).
Essentially this is trying to increase the effective V. E. of the engine. This always sounds like a 'free' power increase.
But both cost money to fit, require modifications, can affect reliability, shorten engine life, increase fuel consumption. etc.
Superchargers also have the downside of using some engine power to drive them. They often require the compression ratio to be lowered, (reducing the V. E. of the engine), they heat the intake, reducing potential power gains, unless an efficient heat exchanger is fitted. (not so easy to do on a 500).
I've sometimes wondered about the volume of air being pumped by the cooling fan around the engine under the cowling in order to cool the engine.
If this air was to be collected, channelled through a heat exchanger and then fed to the carb. intake, would this not be a sort of 'free' supercharging?
Reminds me of my little Honda motorcycle in the 1970's. I had the bright idea of fitting a 180 degree elbow to my carb intake and pointing it forward into the air stream. I'm sure that bike went much faster as a result. :devil:
Al.