Has anyone here checked or even tried to see if the flywheel on these bikes can be lightened? I have a couple of friends with a Ducati 998, & 748 and they did this to thier bikes and got a huge noticable difference in how fast thier motor would rev up. I know the clutches on those bikes are different than ours (dry clutch vs. wet clutch) but I do believe ours should have a flywheel also, and if so I would like to do this to mine. Any info on this would be greatly appreciated. Thanks!
Off the top of my head, the biggest reason that it is not a practical modification on a VFR is that the bike weighs too much. The small amount of energy that would be recovered from not having to accelerate a slightly heavier flywheel/crankshaft assembly would probably not make that much difference in the overall performance, given the existing power-to-weight ratio. Typically, the heavier the flywheel, the smoother the engine runs at lower RPM's. Any engine, particularly small displacement high compression engines, need a heavier flywheel (or rotating assembly of some kind) just to idle at a reasonable speed. If you lighten the flywheel, it changes the mechanical stresses on all of the moving components due to changes in acceleration/deceleration and at what particular RPM parts will resonate. Without being a complete boring on the topic, this is not a straightforward modification on a motorcycle engine due to their high RPM nature. Parts that have proven reliable in a standard configuration can fail in a modified state, many times in a seemingly unrelated area.
I appreciate your comment. I have also wondered about the reliability if I did the mod. So far my friends Ducati 998 has had it for a bit over a year with no problems, as far as the one with the 748 he just did it about a month ago so we will see how his bike holds up. If I did do it I wouldn't even attempt it until winter, thats if I even do it. I want to get more input and see how both of my friends bikes hold up before I go through with it, thats if its even possible.
And just so I am not being a complete "wet blanket" on the idea, it certainly is possible. Like all modifications, it is always a matter of what kind of performance you are looking for, how much reliability you need, and how much you are willing to spend. I would almost be willing to bet that Ducati expects modifications of various sorts, and designs their engines to withstand them for some reasonable amount of time. And you know that Honda and the affiliated racing teams made their racing V4's as powerful and rev-happy as they could, knowing that they only needed to live a short amount of time. When you think about the target audience of the current VFR, Honda probably figured, worst case, we'll spend 80% of the time touring, 15% of the time semi-sporting and 5% of the time seriously sporting. So it would stand to reason that they've tweaked the motor accordingly. I looked at the shop manual between this post and the last, and the only "flywheel" is the crankshaft counterweights, unless I missed something (somebody correct this if it is wrong). Since they are part of the crankshaft, you would be talking complete engine disassembly and either modifying the existing crankshaft, or replacing it with a lighter version.
If thats the case, then I would most likely not be attempting this. I wasn't sure if they did have a flywheel or not, thats one of the reasons why I did this post. Thanks for looking into that for me.:thumb:
I talked to a couple of my friends after posting this, and one of them brought up a good point on this. He suggested that if I did go through with it and shaved weight off of my crankshaft that as they are doing so to have it balanced at the same time therefore eleminating the need to have some of those balancers on there. What do you guys think? Would it be worth it, or would I be dissapointed with the outcome?
The crankshaft is already balanced. If weight is removed from the counterweights by anybody who knows what they are doing, they will remove the same amount of weight from each counterweight. Motorcyclist or Cycle World, in the last couple of months, had somebody ask a very similar question in one of their "Tech Questions" section. The explanation of crankshaft balancing was pretty good. If you have the issues, it's worth looking up. Essentially, the VFR V4 is two 90 degree V-twins coupled together, so the primary balance is not an issue. I think that the crankshaft could be absolutely featherweight, and as long as all the individual components were balanced (pistons with rings, wrist pins, connecting rods with bearing inserts and crankshaft), the overall "static balancing", such as it is, would not be much of an issue. What would be an issue is the crankshaft accelerating, decelerating and twisting in an untested and non-engineered fashion. Even if the crankshaft itself did not fail, the entirely new set of harmonics introduced could cause other components to fail. Additionally, your idle speed would likely have to move up several hundred RPM at least, and the low speed running would be rougher. Probably your best place for an answer would be one of the specialty crankshaft people, since they do this for a living. I can recall one that handles bike cranks; FALICON CRANKSHAFT COMPONENTS, INC. 727. 797. 2468 Currently, they do not list the VFR in their online catalog, but it never hurts to ask.
Thanks, I'll have to give that a try. Again I'm still not dead set on doing this, I want to find out if it would be a good enough gain verses the cost of doing and of course if it will affect the reliablilty of my motor drastically or not. I'm geussing it would do more harm than good at this point, so as for now I'm leaning more to the don't do it side. Anyway, thanks again for all of your input Lgn001! Its nice to know there are others out there who actually look at things the way you do. Keep it up!:thumbsup:
Howdy VFR Guy 2000; I like your idea, for years small cc MX bikes have been built with light fly wheels. The lower recipicating weight makes the enging accelerate noticably quicker. My experience with lighter flywheels has been with a 350CI Chevy Camaro. I origionally bought a forged flywheel of standard weight. We did some experimenting and removed about 15% of the flywheels weight,via a lathe. The change really helped the car accelerate. We used the lightened flywheel all season without any damage. Even though I have had a good experience with lightening the flywheel, I am not at all suggesting this would be a safe modification on a VFR engine. But some of the shops that build high performance sport bike engines should be able to give us some basic knowledge on a modification such as this. eddie
Yes that is why I am intreeged by this idea, and after seeing how both of my friends Ducati's ran after doing this on thier bikes. However this will be much harder to do on our bikes hence there is no actual flywheel. I'm still kicking it around though, we'll see what I decide after I weigh all the pros & cons and get more info from the pro's. I will keep everyone updated.
