| Author | Message | ||
     Toniportray |
I was just rumbling around in Oakland today when I suddenly came up with the question of why motorcycles are made with the exhaust at the front of the cylinder and the intake on the back. It seems like it'd be better to put the intake at the front of the cylinder to utilize ram air and to put the exhaust at the rear of the cylinder so that the pipe doesn't have to go through that stupid 180 degree turn around, reversing the flow of exhaust fumes. Am I the only person who's ever noticed this? People spend extra money in order to reverse the design of the intake by purchasing and installing intake pipes that stick out funny so as to invert and collect ram air into the carburetor. We also have to pay for a twisted exhaust pipe that otherwise may have been cheaper to put just a straight pipe coming from a rear-facing exhaust port. Whats the deal with this backwards design? I can't imagine it being much of an issue to route the exhaust pipe to the side of the bike (and to the rear)so it doesn't put a bunch of heat on the central components of the motorcycle. As much as I love the Firebolt, I'm always puzzled why the exhaust pipes make three 180 degree turns before expelling the exhaust gases. Seems like it'd be smarter to just flip the exhaust and intake around and run the exhaust under the seat or something... The only reason I can forsee the current setup with the exhaust in the front of a motorcycle is to cool the exhaust pipes better... I suppose it could be an issue of engine rotation, but if it were, then why not put the primary/transmission on the right side of the motorcycle? That would resolve any issue of the crankshaft rotating backwards. And why not just run the crankshaft directly to the transmission (still with a clutch plate) using gears instead of these short lived primary chains? Anyone have any interesting insight as to why all our motorcycles are backwards (or any of my other endless questions)? | ||
| Akbuell |
Space considerations and cooling. Having the intake in the back provides room for it. Having the exhaust in the front provides cooling, and allows for a reasonable amount of space to put in a muffler, and provide adequate volume for the system. | ||
| Buellinachinashop |
"Seems like it'd be smarter to just flip the exhaust and intake around and run the exhaust under the seat or something..." Mass Centralization my friend. Mass Centralization. | ||
| Jaimec |
You want the exhaust in front where it can get the most cooling air blowing on it. Putting it in the back, behind the hot engine block, can give you heating problems, even in a water-cooled design. | ||
| Ft_bstrd |
Usually fuel delivery is better compact with exhaust routing allowed to be a little more free form. | ||
| Bosh |
You mean like this?  | ||
| Spiderman |
Yeah and you see how well they did... | ||
| Skinstains |
that used to be the hot set-up on the old Triumphs. Spin the head 180. cool fresh air in and spent gasses straight (almost) out the back. I guess it's sort of like having a pressurized airbox.?! You'll note that you don't see any of them like that anymore. | ||
| Froggy |
I was wondering the same thing a while back when looking at some naked I4's. I came up with the same answers above for both pros and cons of each way. | ||
| Swordsman |
If overly-hot exhaust is such a problem that it needs to be in the front, then why do people wrap headers to keep the heat in? ~SM | ||
| Spiderman |
then why do people wrap headers to keep the heat in? Hot exhaust gas moves faster. While putting the intake exhaust 180 (head) may make for a more efficient motor, it would be a logistical nightmare! All new Hyper bikes and Buells need a specific size air box, whether it be pressurized or still, to meet EPA standards of noise and emissions. On top of that there is the heat factor. You think a CBR or duck is hot now! Wait till you have exhaust temps of 400+ degrees right under your gas tank or boy bits (on a in line four that is) on a Buell they have done it before, It was called the RR100 it used a XR1000 motor which was efficient BUT You had to sync carbs AND the front head carb and exhaust stuck out so far on the Sporty XR1000 you leg had to stick out extra not a compact package for a slick handling sportbike or street bike, let alone how you would even begin to do that with a XB frame! | ||
| Bosh |
"Yeah and you see how well they did..." Once they got some of the fuell injection issues worked out that bike was a ripper. They went under because MX is a hard market to get into, coaxing racers away from their beloved Kamahondukis at +2K the cost isn't easy. If having an exhaust behind the cylinder head is such a big problem we'd better get rid of our Buells quick before they burn up  I'll buy the logistical nightmare argument though especially on a V Twin. | ||
| Spiderman |
Inline 4 as well. Imagine that big airbox on the front then the exhaust wraping and snaking around the back. Not only is all that heat going to be contained uner the seat but it is going to transfer to the starter, you, and now the pipes will not be long enough for power/tourqe and EPA. | ||
| Bosh |
Yea... the airbox could be a problem. The exhaust though could almost be a straight shot. 4 into 1 straight down to a Buell style muffler and out the front bottom. Lots of options. | ||
| Simple |
Crankenstein... http://www.bikepics.com/pictures/1016170/ | ||
| Spiderman |
You draw up working and cheap (ie easy to manufacture and build) plans and you will be a millionaire Bosh... | ||
| Birdy |
Looks like they let you have it both ways with the bikes we ride. Front intake rear exhaust on the rear cylinder could that be why it gets so hot?  (Message edited by birdy on August 16, 2008) | ||
| Bob_thompson |
Has anyone thought about the efficient manner in which the BMW boxer is configured. Cylinders right out in the wind stream, carbs/throttle bodies angled up slightly and somewhat in the wind stream and nice turn for the exhaust to exit back, again out in the wind stream. Low center of gravity, great handling and now some pretty good H.P. Maybe not a better and more efficient way to do it. Just suffers somewhat from understanding and acceptance........and its kind of expensive. I really like these and have has a couple but I love my new 1125R. Bob | ||
| Djkaplan |
There have been lots of racing motorcycles configured with rear pointing exhausts. Some Yamahas 2-strokes actually had 2 conventional cylinders and two rear exhaust cylinders on an inline-4. The Tuluie snowmobile engined bike that made such big splash a few years ago was also configured like that. http://thekneeslider.com/archives/2006/04/21/tul-a ris-two-stroke-racer/ This layout has been tried many times with varying degrees of success. |
