Why does the Yz450 exhaust circles the motor?

Was at the dealer the other day looking at Wr's and noticed the Yz450 does something the WR doesn't do, the exhaust circles the motor. Curious on why the Yz would have the heat producing exhaust entirely circle the motor then having it go from back of the motor straight to the exhaust and keeping it all cool, any help why?

yamaha-2015-yz450f-motocross-blue-new-can039t-compare-to-any-moto-bike-1.JPG

Well if you dont already know I believe they went to this bizzare design to change the center of gravity. Since the tank is more mid on the bike and airfilter up front etc. As for the wrap around exhaust i guess they did it to aid the center if gravity as well and perhaps if they made it straight back it may interfere with the suspension etc. Just my guess though...

The longer head pipe changes the power delivery and reduces sound output. I think.

Yeah i dont kno why i didnt think of that they probably did it to make it have the required length for the right tuning

The reason starts with the cylinder being tilted rearward, and the exhaust port being moved to the back of the head.  That was done to, one, move the center of mass closer to center, and two, to allow for the brutally straight intake path the air in the engine has.  The problem that was created was how to handle the exhaust system.

 

To function properly, the header, and the whole system, must be at least a certain length (varies with the particular engine and application).  Yamaha's first solution for the '10-'13 models was to coil the header up under the seat, but this was a little crowded, and still left the muffler in somewhat more of a rearward position than they liked.  So, based on an idea from Doug Dubach, their next approach was to run the header "around the block" to get it long enough, then move the muffler farther forward to connect. 

Ah, thanks guys for clearing that up.

The reason starts with the cylinder being tilted rearward, and the exhaust port being moved to the back of the head.  That was done to, one, move the center of mass closer to center, and two, to allow for the brutally straight intake path the air in the engine has.  The problem that was created was how to handle the exhaust system.

 

To function properly, the header, and the whole system, must be at least a certain length (varies with the particular engine and application).  Yamaha's first solution for the '10-'13 models was to coil the header up under the seat, but this was a little crowded, and still left the muffler in somewhat more of a rearward position than they liked.  So, based on an idea from Doug Dubach, their next approach was to run the header "around the block" to get it long enough, then move the muffler farther forward to connect. 

I think Yamaha just took a short cut to save a few bucks.  Yamaha has the engineering capabilities to design a rear facing exhaust system with what ever requirements needed (back pressures and cambers etc)  listening to a Dubach on engineering aspect of exhaust design is like asking the the sta-puff marshmallow man and is a half ass quick fix at best . Doug is a great rider not a engineer.  The tilting cylinder and rear facing head is such a great design for lowering the center of gravity (CG), straight intake and exhaust paths. and allows the gas tank to be put relocated where the air box was to even lower the (CG) more. lower gas tank location with fuel pumps and fuel injection will be the standard on all bikes real soon (see link below).   The theory of exhaust lengths can't be changed by a major motorcycle manufacture with the engineering capabilities of Yamaha doesn't hold water.   https://www.youtube.com/watch?v=i13gr4NC2Kw

Edited by RJHILL

I think Yamaha just took a short cut to save a few bucks.  Yamaha has the engineering capabilities to design a rear facing exhaust system with what ever requirements needed (back pressures and cambers etc)  listening to a Dubach on engineering aspect of exhaust design is like asking the the sta-puff marshmallow man and is a half ass quick fix at best . Doug is a great rider not a engineer.  The tilting cylinder and rear facing head is such a great design for lowering the center of gravity (CG), straight intake and exhaust paths. and allows the gas tank to be put relocated where the air box was to even lower the (CG) more. lower gas tank location with fuel pumps and fuel injection will be the standard on all bikes real soon (see link below).   The theory of exhaust lengths can't be changed by a major motorcycle manufacture with the engineering capabilities of Yamaha doesn't hold water.   https://www.youtube.com/watch?v=i13gr4NC2Kw

 

So, they just re-write the laws of physics, and the rules of business then...

 

...and using a 'dumb rider' to help engineer a world-class motorcycle should never be done.....like The Jones Brothers and Yamaha/Honda/ISLO, or Roger Decoster and KTM/ Suzuki, or Preston Petty and Suzuki, or Ole Peterson and Suzuki, or Horst Lietner and KTM,  or about 25 other riders who have signifigantly altered the engineering paths of the big 4 MX brands......

 

You should do a little reading.....

 

http://www.mxworksbike.com/index.php/blogs/terry-good

Edited by KRANNIE

.....Brad Lackey and Kawasaki...

The 2016 WR450 does have the YZ style wrap around exhaust while 2015 and older does not.

Doug is a great rider not a engineer. 

 

Doug Dubach may or may not be an engineer, but he is definitely one of the best test riders in the business, and can isolate, identify, and suggest corrections to both engine and chassis behaviors few other people even notice.  He's been instrumental in the development of the YZ-F line from the beginning.  When he talks, they listen.

 

I fail to see how there is a money-saving aspect to the "round the block" pipe, which requires making and fitting an extra section, versus the "tornado pipe". But there is no difference in the tuned length of the pipe as a result of them taking that route, so I have no idea what your complaint about it is, and certainly not what, if anything, the TM test had to do with the matter.

I think Yamaha just took a short cut to save a few bucks. Yamaha has the engineering capabilities to design a rear facing exhaust system with what ever requirements needed (back pressures and cambers etc) listening to a Dubach on engineering aspect of exhaust design is like asking the the sta-puff marshmallow man and is a half ass quick fix at best . Doug is a great rider not a engineer. The tilting cylinder and rear facing head is such a great design for lowering the center of gravity (CG), straight intake and exhaust paths. and allows the gas tank to be put relocated where the air box was to even lower the (CG) more. lower gas tank location with fuel pumps and fuel injection will be the standard on all bikes real soon (see link below). The theory of exhaust lengths can't be changed by a major motorcycle manufacture with the engineering capabilities of Yamaha doesn't hold water. https://www.youtube.com/watch?v=i13gr4NC2Kw

If I was going to make a comment on this I would write "arrogant ignorant" but I will not

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