Yamaha XS650 backfire - Page 10

 

Two smaller valves that fit in the same sized combustion chamber have
more peripheral area than one larger valve. The air starts flowing at
lower lift off the seat.

Camshaft designers start figuring the cam duration from when the valve
first lifts 1 mm off the seat until it returns to 1 mm off the seat.

Yamaha tried 4, 5, 7, and even 9 valves per cylinder, before settling
on 5 valves per cylinder on their Genesis motor designed around 1985.

My FZR1000 has 5 valves per cylinder, but Yamaha is giving up on the 5-
valve design because it doesn't deliver power the way they want it to.
If they lower the compression so it will rev, it loses mid-range
power. If they increase compression to get mid range, it won't rev.

4 valves per cylinder seem to be the best compromise. Honda has revved
4-valve engines up to 25,000 RPM.

What the heck? I very seldom use even 8000 RPM. Maybe once or twice in
a long day's ride through the back roads...


When the Japanese companies started producing 4 valve per cylinder
engines, the aftermarket cam grinders figured they could just use the
same long durations
on their offerings to the motorcycle hot rodders, but they were wrong.

Their cams didn't work well at lower RPM with the amount of
compression ratio the factories were using.

The new 4-valve engines did better with less duration and a little
more lift...

Most shade tree tuners don't understand what compression ratio does
for them anyway. You need just enough compression ratio to allow your
engine to get over the first hump in the torque curve and through the
mid-range flat spot into the second hump in the curve.

That's where the real power band starts. Too much compression keeps
the engine from taking advantage of the inertia effects of air in the
intake and exhaust systems...

 

Earlier

And nothing to do with the desire to keep down costs? The 5-valve engine
was/is superb. Even Ferrari used the tech.


--
BMW K1100LT  Ducati 750SS  Honda CB400F  Triumph Street Triple
Suzuki TS250ER  Coo, down to just five bikes!
If you don't know what you're doing, don't do it. And RTFM.
chateau dot murray at idnet dot com

 On Jul 6, 11:41 pm, totallydeadmail...@yahoo.co.uk (The Ever Boor)
wrote:


And why, pray tell, have the folks at Yamaha re-designed the starter
clutch system to put it on the end of the crankshaft, where it can be
accessed more easily?

 
On which FZR1000 have they done this, then?

 wrote:


They haven't done it to the FZR1000, and never will, but they did
redesign the Seca II to move the starter clutch onto the end of the
crankshaft where it belongs.

The folks at Triumph also learned their lesson about burying the
starter clutch and later designs relocated it to the end of the
crankshaft.