| Author | Message | ||
     Arry |
The latest Cycle World magazine (feb '15) has several new bike reviews, several are dual sport or ADV bikes. The new Ducati Multistrada has variable valve timing (a first on motorcycles?). Instead of a fixed timing for all RPM's, it tailors the valve timing to the engine speed. The short article mention the peak HP and torque gains, but the cool thing is, power gains through out the rev range (a very good thing for a dual sport/ADV). Not a new concept, but not easy to implement. | ||
| Arcticktm |
Don't forget about the Honda VTEC engine that's been in the VFR's for quite a while. It's not the same as their automotive VTEC systems, but it is a method to vary valve timing. Sounds like the Ducati system is quite a bit more versatile than the Honda VFR system. Since variable timing is quickly becoming the norm for car engines, it is a little surprising how long it has taken to get into motorcycles. Perhaps just because cars need to have efficiency AND performance, where motorcycles still mostly cater to either performance or low cost/efficiency, but not both. | ||
| Buewulf |
The Honda version in VFRs is kind of a misnomer... It does not vary valve timing at all. All it does is switch from 2-valve to 4-valve operation at a particular RPM. The Ducati system is just like the automotive varieties in that the valve timing itself is altered depending on a host of variables. | ||
| Mark_weiss |
Automotive applications also generally have room for bulky apparatus. | ||
| Natexlh1000 |
My Honda Fit had the valve deactivation version too. If I left in second hear and stomped its little pedal, you could notice it change over when it got to about 3500. It's a great little engine with a broad torque curve. It has sneaky stuff too. Like the crankshaft is offset by a small amount so that the power stroke is more straight to reduce the piston skirt loads. | ||
| Arcticktm |
Thanks for correcting my mistaken memory on the VFR system. I was mistaking it for some of the earlier VTEC auto systems. I now recall reading about the 2 vale/4 valve strategy. Should have double checked first. Nate - I think the crankpin offset you mention is pretty commonly used in small auto engines. I recall a professor at school teaching us how to calculate an appropriate amount of offset using the old GM Quad-4 engine as an example. That was back in the late 80's. The main benefit (at least to GM view at that time) was reducing piston slap that made an objectionable noise especially in inline 4 cylinder engines. It makes sense that reducing that slap would also reduce side load spikes on the piston skirt. Even with that design, no one would accuse the Quad 4 of being a refined 4 cylinder compared to the Toyota/Honda engines of that time, or compared with any engine today. I am pretty impressed how smooth and refined sounding my little 1.6L turbo engine is in my car. Except it is a bit rattly when it is cold. | ||
| Buewulf |
"I think the crankpin offset you mention is pretty commonly used in small auto engines." If I am not mistaken, Yamaha also uses that strategy with the FZ-07, FZ-09, R1 and their motorcross bikes. Kawasaki is also a believer in the practice, though I don't think they really advertise it as a differentiator. Off the subject a bit, but offsetting the cylinders from the crank has been around since the steam engine. It was common in many auto engine by the early 1900s if I remember correctly. | ||
| Tootal |
BMW's high dollar automotive engines actually used variable intake valves to control engine speed instead of a throttle body. I never saw how it worked but the article was very interesting. I loved how the later M3 engines used a lever to transfer the rotary cam motion to an in line motion to push on the valves. Much cheaper than using buckets and shims! That might have made it to their motorcycles, I don't keep up with them anymore. | ||
| Mark_weiss |
Suzuki started using the single-finger cam follower in the early '90s. No longer though. It DID make valve shim changes very easy. BMW uses a similar system on the S1000 and also on their newer cam-head twins. | ||
| Tootal |
Thanks Mark, that would make sense, great design. Speaking of great designs I really appreciated EBR's cam design that opens one intake slightly before the other one causing a swirl effect and atomizing the fuel much better. That's really cool stuff. I never build my engines for top HP or Torque but to have a great combo along with efficiency for real world riding, not a dyno war. Getting the EBR engine higher HP and extend the mileage to over 50 is amazing.  |
