Ti Valve Info (426)
Posted August 29, 2000 - 07:28 AM
From Yamaha's Literature
"The intake and exhaust valves have been changed from steel to titanium., and in doing so the total weight of the five valves has been reduced from 95 to 63 grams (40% reduction) This has enabled a reduction in valve spring rate (16% on intake side, 18% on exhaust side), the combined effect of which is better response and reduced horsepower loss."
Posted August 30, 2000 - 03:52 AM
Posted August 30, 2000 - 04:21 PM
Hmmmm, I wonder if I could buy the Ti valves and just slap them into my '00 WR400?
You'd need the new valve springs too.
Ever turn the motor over with the spark plug out? See how there's still resistance even without compression? A little of it is drag from rings and bearings but probably 90% of it is trying to push open the valve springs. Think of how much drag that is at high RPM. The benefit of light Ti valves is that you can use lighter springs to control them. Using lighter springs is where the power gain is.
Also, there may be a higher rev limit due to lighter valves floating less but I don't know if Yamaha would change that. You'd need to re-map your ignition to take advantage of that anyway.
I'm sure we'll know soon enough if the valves and springs fit our bikes, I imagine there are a lot of people waiting to check that out. Hopefully the cams are the same and the only difference is the valves and springs.
MotoGreg - The voice of absurdity
'99 WR400 - 'Cause thumpers rule and two-strokes drool!
'92 GSXR 7/11 (But I wanna get a dope 916)
I might let you visit my photo album for $3 - ENTER AT YOUR OWN RISK - DANGER LURKS WITHIN
Posted August 31, 2000 - 06:12 AM
I did exactly that last weekend. I took apart the engine and checked out the valves, piston, rings and such. I did notice the huge amount of pressure it took to depress the valves. I figured I'd need valves and springs to make it work. Since these valves are on a 426, I assume the cam shaft is different, but I don't know about the size of the intake and exhaust valve heads. They might require a bigger port to seat properly. . . .have to find the tech specs on the 426 engine to check it out. You're right, someone will try it. . . .
'00 WR; YZ modified, DSP exhaust system & UNI air, Jetting by Clark, James & Bryan. . .