Still a sissy above 8,000 RPM's

[sxty8goats]

Read the thread this afternoon and brought her up past 12K on the ride home. Sweetness. Not sure I'll be winding her up that high on a day to day basis, I still want to keep the MGP's up there, but man does she sound sweet with the scorps singing..

 

[BigB]

4-6 rpms cruising, 6-8 rpms shifting while cruising, 8-12 rpms the fun zone. the engine is silky smooth up there, in fact i've changed my riding habits from cruising along at a vibration-filled 5-6 rpms to bringing it up to the smooth zone around 7-8 rpms. The bike just likes to be there and the cars around you know where you are. A win/win situation.

 

[deeptekkie]

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.

What you said, (total agreement): Now add pushrods to the equation, (no overhead cams), and one can see why these type engines float the valves at such low rpm's. What's cool about our bikes is not only the high redline but the torque available down low as well.

 

[Kamloops]

I showed my buddy who rides an fz6 this thread.

His response -

""Boy does she love it between 12k and 14k She wants to be spanked hard - and boy do I give it to her hahahhaha""

 

[RJ2112]

What you said, (total agreement): Now add pushrods to the equation, (no overhead cams), and one can see why these type engines float the valves at such low rpm's. What's cool about our bikes is not only the high redline but the torque available down low as well.

This is another benefit of the little valves, and the 'direct' action.... almost zero flex in the components, and since the only mass is the valve itself (plus the tappet, and shim) the springs don't have to be as strong.... so there's a lot less friction between the cam lobe and the device operating the valve. More engine power can go to the back wheel.....

As far as low end torque, there would be more if they had implemented something like the VFR uses, and operated the second pair of valves at a 'cut over' RPM.

Torque down low is mainly developed by how well the fuel is atomized. The injectors have helped with this a bunch, compared to big jets in simple carbs...... decades back, you couldn't get a motor that ran well at 6,7,8,000 RPM to run well at all, at idle. The valves were big, and stayed open for a long time.... good for high speed power because they could 'flow' a lot of air relative to smaller valves and less aggressive lift and timing. The trade off comes in how well the air flowing into the cylinders can rip apart the droplets of fuel.

The finer the droplets, the more surface area, and the more quickly the fuel burns. Rapid controlled combustion being the goal. Little valves on 'long stroke' motors with very little valve 'overlap' have strong intake vacuum... the air ripping into the cylinder breaks up the fuel very effectively.

Reduce the strength of that vacuum by increasing the volume of air (which 'slows' the air flow) and the droplets tend to be bigger..... harder to burn. That means less power for any given level of fuel added to the cylinders.

Variable valve timing has turned that on it's head. Now, you can have your cake and eat it too. Not only can you radically change the airflow, you can tailor the FI and the spark advance to match. The full blown SS bikes take that a step or two further, with the valve in the exhaust, and the flappers to change the volume of the air box.

There's so much adjust-ability there, the added weight and complexity of the vvt systems don't make a big enough difference to be included. The multi point laser drilled injectors make the fuel droplets way smaller than what can be accomplished with anything else, so the engine doesn't 'suffer' as much in the lower RPM portion of it's range.

I suspect the reason the FZ6 does as well as it does below 5K has to do with the 'simplified' intake system being tuned for mid range.

It's one of the most successful 'tuned for the street' racing motors I have experienced. Not much lost on top relative to the YZFR6 version, but it's more tractable.

The neutering they gave this rig going to the FZ6R is shameful. If I buy another FZ6..... it won't be the FZ6R.

 

[kyle]

There's something about the stock exhaust that does give the bike a sound like it's being punished somewhere around 6-10k...after it gets closer to redline it sounds a bit more pleasurable to me. I think it's because of the way the stock pipes cut all the bottom end out of the sound so you hear more of the head sounds (valves, rockers, etc). Had a Blue Flame pipe on my R6 that I had previously and the sound from that begged to be revved. Wish pipes weren't so damned expensive, or I'd have already ordered one for the Fazer.

Either way, I'm not afraid to rev it. I haven't lifted the front yet, but it has gotten a little light a time or two (bars get a little twitchy to let you know).

 

[Moses195]

I think you're right about the stock pipes!! Thanks.