Why do motorbike exhausts exit the front of the engine?

Is there a reason why motorbike exhausts exit from the front of the engine (generally...V configuration excluded). If it exited from the back you wouldn't need such a convoluted run of pipework, it would be easier to package..? Is it because of other engine components dictating where it goes, crank position etc??

Go on! Tell me.

[yorkie_chris]

Yeah you need a bloody great airbox to get the right resonance, and straight downdraft intake ports for good power. It's very hard to do that, you'd end up with a set of carbs stuck up near the headstock and nowhere to put the airbox.

Pipe length is also important to get correct resonance for scavenging, I think the pipes end up close enough right as they are.

Some 2ts use rearward facing pipes to good effect, RD500, RG500 for couple, they have carbs on the side.

Ah yeah. Good point. Didn't think about the induction. Carbs though? What century do yuo live in Chris?

scoobs, that avatar makes you look like the wrestler from the 1st spidey movie..

Originally Posted by Razor

scoobs, that avatar makes you look like the wrestler from the 1st spidey movie..

Off topic, but spot the difference.

[fizzwheel]

Originally Posted by Scoobs

If it exited from the back you wouldn't need such a convoluted run of pipework

Didnt the Foggy Petronas bike, have the exhaust exiting out the back as you suggest ?

If so that had IIRC a rather complicated exhaust pipe setup and I think they had heat issues with it as well caused by the exhaust needing to be the right length and having to curl round on itself to get the motor to run properly.

[Sid Squid]

As Chris says it's mostly a matter of physically packaging the various bits, plus for handling reasons the swingarm would be as long as is practically possible, this means the engine will have to be as far forward as it will fit, meaning there's little room for the various induction parts to be fitted to the front of the engine.

Not all bikes have the engine and exhaust so arranged, one model of TZR250 springs to mind, (3MA perhaps?), also some drag bikes have the head reversed, but they have very long chassis so there's no such space restriction ahead of the motor.

[yorkie_chris]

Originally Posted by Scoobs

Ah yeah. Good point. Didn't think about the induction. Carbs though? What century do yuo live in Chris?

EFI

Bike engines peaked when they made GSXR1100K. EFI is just to keep some @rsehole in brussels from whinging so much he'd spill his low-fat capuccino all over his vegetarian option light lunch in furiously green indignation. The tw*t.

Randy "Macho Man" Savage haha, very nice

Originally Posted by yorkie_chris

EFI is just to keep some @rsehole in brussels from whinging so much he'd spill his low-fat capuccino all over his vegetarian option light lunch in furiously green indignation. The tw*t.

Or it may be that it is generally more reliable, has better starting capabilities, and better general economy; things that are important to bike and car manufacturers.

But please continue...