Why do motorcycle manufacturers insist on setting the engine so that the heads point forward, and then you need aftermarket companies to design convoluted and expensive exhaust systems that manage to get the airflow twisted round to the back?
Why don't they simply point backwards and have a half-exhaust that sticks directly out the back?
_________________ MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-
I'd guess it has to do with packaging (fitting engine in frame, center or gravity, etc.). Figure a UJM inline 4. I think the engines are canted forward for low COG and to prevent tank from being a chin rest whilst you're sitting straight up. If you were to mount carbs on the front of that engine, they would need a funky set up. They'd need to be like ..... 2 sets of hanging DDs (or something like that?!).
Maybe it also helped with cooling older air-cooled motors. Think of the flow of air hitting the exhaust port side of an engine (2 and 4 stroke). I can envision the finned ex. manifold brakets of various makes.
on the 2 stroke V-twins, its just simpler to have a central induction system (one airbox, one ram-air box, racked carbs....). I believe honda has a patent on this system (V engine config. with central induction). Besides various RS250s and NSR250s, I have only worked on a 3XV (?) TZR250 and it was a nightmare with seperate carbs, airboxes, cables.
Now where's Master Matt to chime in and show my ignorance.
Remember, there's no such thing as a stupid question, just a stupid answer!
looking at your handy artwork made me think of something else. you'd have to be a hell of a welder to get all those expansion chambers fitted up if they came out the ass end of the bike. look at any japanese mx 2-stroke. they have to twist around that fat chamber in front of the engine.
An engine starts at the airbox and filter, then the fuel is added by carb or injection, then the combustion bit and finally the exhaust and silencer.
If all the stuff before combustion had to go infront of the cylinders, then the engine would be under the seat, and the C of G would be no-where near 50:50, as you plus engine = most of the bikes weight, all sat on the back wheel!
Carbs need still air to work properly, and although injection is much better at dealing with forced air it's still easier to work with still air (even if it's pressurised by forced air or turbo's) hence the continuing need for large airboxes.
Why a V twin then? Because it has better primary balance than a parallel twin (I think) so it lasts longer and saps less power.
Manufacturing expansion chambers to fit between the frame rails would be another pain, and the heat transfer to personal body parts is quite uncomfortable I am led to believe! Not to mention frying electrics...
Perhaps a leteral V twin (like a Guzzi) would be best, with a central airbox and rear facing exhausts. But then again, exhaust length is an issue, so the pipe might end up on a trailer to get the proper length! _________________ MC21SP Plaything
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