mrfast
Expert Class
Posts: 114
|
posted March 25, 2003 07:27 PM
Valve angle,Doug?
Manufacturers brag about narrow valve angles in their brochures.In 1996 Kawasaki released todays current ZX750 with an included valve angle of just 20 degrees.All the new ZX's including the new ZX6/ZX6RR have a valve angle of 25 degrees.If narrow valve angles/flat combustion chambers, are so important, why isnt Kawasaki still using the ZX750 dimensions of 20 degrees?
  
|
dougmeyer
Needs a job
moderated
Posts: 2713
|
posted March 26, 2003 07:38 AM
mr,
Steep (narrow) valve angles allowing a flatter combustion chamber are certainly preferable, so the engine designer will try and achieve an included angle of around 20-30 degrees. This range exists because too flat and you loose combustion "space" (also called "headspace"), too wide and the ports have too take too sharp a turn at the valve pocket. Don't forget the valves are at the end of ports and "below "the cams, the engine designer has to take into account the cam spacing and valve operating gear as well as where the injectors/carburetors are and how they will fit in the frame. Too steep and you're up under the "tank" too flat and you're back under the "seat". It is only in a true racing engine that is designed without compromise (make the vehicle fit the engine afterwards) that you'll find the optimum setups for performance. Otherwise it's all a compromise. The exhaust port on the 12 is a perfect example of this. It it is far from optimum, but the exhaust pipe exit location and angles pretty much determine how it looks, not the "best power" design that might be possible were the engine not in a conventional motorcycle.
Doug
|
frEEk
Administrator
ummm... yeah
Posts: 9660
|
posted March 26, 2003 02:54 PM
so i take it the standard engine layout is hardly a good design when it comes to power eh? is there some engine designer's dream layout? or could it be accomplished jsut by completely moving the tank below the seat, flipping the engine back to front (with exhaust ports in rear) then allowing the exhaust to exit almost vertically, with a fairly tight initial curve in the header? granted that curve may be a problem, but using the Serpent's idea of a flattened pipe, maybe this wouldnt be such a big deal?
|
dougmeyer
Needs a job
moderated
Posts: 2713
|
posted March 26, 2003 03:41 PM
To see what an ideal design looks like, look at a F-1 car engine. That's it.
What does that flat pipe thing do anyway? What you're describing sounds a little like Larry McBride's Top Fueler.....
Doug
|
frEEk
Administrator
ummm... yeah
Posts: 9660
|
posted March 26, 2003 06:41 PM
the point of the flattened pipe is said to be smoother flow around a bend. since the outer and inner diameter on teh curve differs less, the gas on the outside and inside wall of the curve can travel closer to the same speed, hence less turbulence. the serpent [sp] pipe is by micron; i'm sure u'v heard of it.
good point on f1 tho. never taken that good a look at their engine layouts. i'll do that!
|
mrfast
Expert Class
Posts: 114
|
posted March 26, 2003 07:16 PM
Thanks Doug,as long as were talking valves, do you think Yamaha has reached a plateau with their 5 valve design? I thought for sure they would top the Suzuki GSXR1000 HP #'s last year but they came up a little short with the R1.I know they make more power on the race bikes but of course those engines are rebuilt more often than a street bike.What changes do you think will put the oem liter bikes above that 155-160 engine HP range and still meet emissions? Pneumatic valves and 18000 rpm?
|
|
|
HOME
NEW TOPIC