Bike designers.... why?

[garth]

Why do bike manufacturers/designers have the inlet port on the rear of the head, and the exhaust on the front????

Surely, it would make more sense to have the exhaust at the back, where the exhaust is directed,and to have the inlet at the front, in the firing line of the air?

Any comments? Or am i just being dumb?

Thanks.
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[Kickstart]

Hi

Probably to get the exhaust long enough and have space for a decent size airbox.

All the best

Keith
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[winwick]

First bikes run better with an air box which creates a pool of cool, still air for the carbs to draw from,yeh you can get ram air but the benefits for normal everyday riding are minimal, the length of the track from the airbox to the carb inlet has an effect on the bikes power characteristics as does the length and shape of the exhaust down pipes.
Modern sports bikes have the airbox above the engine but as you say the carbs are still behind the cylinders.
If you look at a V twin you'll notice that the exhaust from the rear cylinder usually takes a windy route to the rear of the bike in order to get the optimum length.
Yamaha did do a reverse cylinder TZR250 (3ma model i think)
These are all just initial thoughts that have sprung to mind and all of these reasons could be total bollocks but they're the best i can offer

[Aikman666]

First of all having your airfilter at the front would choke it up with all the crap from the roadsurface. And i think having the exhaust at the front is due to the backpressure of the gasses, i could just be talking crap though
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[mchaggis]

Ease of packaging for the most part I should think. Would you really like to try making space for a hot exhaust through the centre of the bike? Similarly, would you like to try fitting the carburettors and inlet system in front of the engine?

The way most bikes are designed makes it much easier to get the exhaust out of the way asap and have it running down the outside. Under the riders backside makes the perfect space for all the extra bits like the airbox, battery, electrics, coolant tanks etc.

Having said that, there are newer bikes with the airbox in the space where the front of the fuel tank used to be. However, like said before though, the length of the exhausts is very (almost most) important to the engine performance, and they know what they are doing with the current design anyway. A design with the exhaust and inlet back to front would be quite a fundamental shift.
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[binge]

Exhausts come out of the front of the engine directly into cool air. Better cooling of the exhausts.

Carbs behind engine, Keeps them warm I suppose, Stops them freezing?

I may be talking complete shite. But just a try?

<|Ben|>

[cagiva gezzer]

https://www.off-road.com/dirtbike/aug2001/cannondale2002/REVERSED%20CYLINDER%20HEAD.jpg

Cannondale make reverse head engines. I don't think they ever really cut it competition wise and i think cannondale have gone tits up....
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[MarJay]

A number of manufacturers have tried it and pretty much all of them have gone the way of canondale...
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[map]

There's some pretty complex dynamics going on inside the engine. The fuel and air mixture is designed to be an additional cooling to the cylinder head. The exhaust design is also important to balance the pressures being generated.

However, that said soon carbs will be old hat. The need for tighter emissions will mean most bikes go over to fuel injection. So this, in theory, would allow more flexible and imaginative engine designs. Downside of that is that it's very rare to get a totally new engine. Most are refinements of what already exists (if it isn't broke don't fix it).

The only new(ish) engine design I can think of is the one intended to make 2-strokes more environmentally friendly. It's a hybred with a 2 stroke top end and a 4 stroke bottom.
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[Big Pete]

packaging is part of the reason , with air cooled high performance engines keeping the exhaust valve cool is difficult, so they are put into the coolest airflow available. Overall bike length and mass centralization also tend to drive the current layout. Reversed head engines have been done before, drag race Triumphs had it done regularly in an attempt to get some ram air effect, but its not very effective.
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[gimpy limp]

does seem abit silly don't it having the inlet at the back and on this engine their covered by side panels:
https://i15.ebayimg.com/02/i/03/cb/ab/84_1_b.JPG
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