I'm averaging much higher rpm's but it still seems like I get a lot of torque and speed at lower rpm's. By the time I get up there in 2nd or 3rd I'm way over the speed limit! And I still think it sounds "Hurtful" above 8,000!! I know it will do it but I'm old school. I know this has been mentioned a lot so be nice. Is "erci" still around? He started out around the same time as I did and short shifted as well. And I'm a F1A fan for 15 years and watch the 2.4L V-8's crank 19,000 rpm's every race. I've been out of work for 4 months and almost sold it back to the Dealership last week but I just couldn't!! Something about her just screamed NOOOOOO!!!!!!!
Thanks for listening. (5 beers, LOL!)
The thing to remember, is that the engineers that designed this motor knew what they were doing. They balanced a lot of dependencies to arrive at a light, powerful, high revving racing motor.
The little pistons and little valves have much less mass than the components in a V 8 engine. They can be spun to much higher RPM in a safe and controlled manner, as a result.
What destroys engines from high RPM most often, is valve float. With bigger valves (single intake and exhaust) the size of the valve required to get good high end air flow is easily twice the size of the two smaller ones used for equal airflow as in the FZ6 motor. 2 times bigger, means 4 times as much mass.
mass times velocity squared/2 is the formula for kinetic energy.... if two things of different mass are accelerated at the same rate..... the more massive one will have a lot more kinetic energy. Think of a .22 caliber bullet, compared to a .44..... the 44 will knock someone arse over tea kettle, and the .22 won't even feel like a bee sting. A single pellet from a shot gun loaded with bird shot at the same velocity has a tough time punching through sheet rock, due to the mass being so low.
All of the energy put into the valve, to push it open, has to be pulled back out of it to get it to close. Springs do a
pretty good job of pushing the valve back out of the piston's way, as it approaches top dead center. You have to use a heavy enough spring to make sure the valve can get out of the piston's way, at the extreme high speed end of the intended RPM use.
If someone pushes the RPM past the design limit, the springs may not be able to move the valve in time.
This is such a critical thing, there is much analysis done to ensure it cannot happen.... the variation in mfg tolerances, stack up analysis, tensile strength of the materials as designed compared to as delivered.... so many things can go wrong, that the design HAS to have 'margin' to ensure it cannot happen.
Staying away from continuous extremely high RPM operation is prudent..... but I would personally be extremely surprised if Yamaha did not do that to the YZFR6 engine in at least one case with a test mule to see how long the motor would last before catastrophic failure..... the accelerated life motor would have been subjected to this at a minimum.
With a rev limiter, the design team can 'increase' their mechanical margin, simply by stopping the motor from spinning any faster.... that gives another level of confidence against harm.
Me personally, I didn't find the FZ to really get any stronger beyond about 11K..... above that, it was about noise rather than acceleration. Knowing that my bike rarely ventured beyond 11K, I know that the valves were not in any danger of float. The main bearings were not in any danger of contact with the crank shaft, or the cam bearings with the cam.
Knowing that I rarely went past 85% of the design limit RPM.... I know the speeds on the valves were low enough that the kinetic energy never came close to over powering the springs on the valves.
If I spent all day riding around in first gear, with the tach spun up to 12K..... I'd eventually thrash the motor. But even that would take a couple of years.
