Bit of a hijack but maybe interesting to you guys. The engine in the Indian FTR 750 flat track bike that has been absolutely dominating the twins class in Pro flat track racing for the past two seasons, was designed with an easily changeable flywheel on the left end of the crank. The flywheels are available in different weights, and can be swapped in just a few minutes right in the paddock to accommodate varying track conditions.

Flat tract racing is all about finding traction; getting the bike to hook up coming out of the turns rather than just uselessly spinning the rear tire. Heavier flywheels help on slippery tracks. Lighter ons let the engine spin up a little quicker when traction is good.

With the reduction of the flywheel to... nothing I would expect sharper power pulses.  Keep an eye on the splines of the output shaft and the dampers in the rear wheel.

That was a great report, DragBikeMike.
Thank you for taking the time to document your work so well
and for being willing to risk your own bike in the experiment.

You certainly didn't get the results I expected.
I agree with Dave that the crankshaft, electrical rotor, and
counterbalance shaft make up for the loss flywheel inertia.

I had a chance to take a nice long ride on it this morning (about 30 miles).  I am pleased to report that it really runs nice.  

There is no question about improved zip.  Dave's comment on cutting 0-60 time is probably spot on. I assume he used some sort of GPS to measure that. I would not use 0-60 because the launch becomes a factor.  I would use say 45-65 on the freeway.  That way you could stay within legal minimums and maximums and also eliminate the launch which is very hard to do exactly the same from run to run.  Hey Dave, what are you using to capture the 0-60 time?

I wish I had some sort of electronic timing device to evaluate these changes.  The seat-o-da-pants stuff I provide has too many factors that can make you think it's accelerating faster when it isn't.  That's one reason why I prefer very quiet exhaust and induction systems.  I don't want all that racket influencing my interpretation of how the bike is running.  With the lighter flywheel, I can't tell a lot in the lower gears on surface streets.  Probably because it always revved pretty fast in 1st thru 3rd,  but when I get it on the freeway it's pretty evident.  I did a sweet 50-80 uphill run on the freeway and it hauled freight.  Its deceptive because its smoother (for lack of a more descriptive word), but when you start bearing down on the cars up front you realize its accelerating pretty fast.  I really need to get it back on the dyno.

Regarding JOG's question, yes, its worth the trouble.  Is it worth it if you are already running a lightened flywheel?  I don't know.  But if you have a stock wheel, I wouldn't hold back.  Take it all the way down to 3.000".  Make some tools to hang on to it and go have some fun.  I actually suspect that you could get away with using a rattle wrench to reinstall it rather than make the special clamp, but I'm more comfy with applying the proper torque.

Regarding Dave's comment about the induction hardening.  I also noted that discoloration when I first removed the wheel.  Came to the same conclusion, induction hardening of the splines and the surface that bears on the inner race of the main bearing, but it looks to me like it's pretty much confined to the area around the splines.  I use carbide inserts in my bits and those puppys can take a beating.  As soon as I felt the increased pressure on the hand feed I backed off to check things out.  I ran a mill smooth file across the edge of the workpiece.  It was dead soft.  I'm pretty sure I had the bit too high.  I just haven't got around to checking it yet.  I'll let you know what I figure out.  With a little care, lot's of cutting oil, and frequent insert changes the finished product came out OK.  There's always something to learn.


Regarding Verslagen's comment on monitoring output shaft spline and dampers in wheel.  Thanks for the tip.  It's a good observation.  I may not be able to sense the rotational pulses but that big, heavy pully sure does.  I already keep a close eye on that output shaft nut.  When I was doing the cam timing check I was using the pulley nut to rotate the engine.  That nut came loose.  Not good, the bike was new with only about 1100 miles on it at the time.  I have seen some posts on the forum that discuss the problems with that setup.  I personally do not agree with the idea that the nut works loose due to the belt tugging on the pulley during acceleration and deceleration.  I have owned a motorcycle of some sort or another from 1968 to the present day.  Almost every one had a chain drive.  I have never experienced the splines in either the counter sprocket or on the output shaft wearing out.  I think the pulley spline problem is related to the size and weight of the pulley.  If you ever look at a Harley pulley you will note that the boys & girls at the Motor Company don't mess around with cheesey lock-tab washers.  They slather up the threads with Loctite 271 and torque the daylites out it, then they lock it in place by installing a hardened socket head cap screw that bears hard on the appropriate corner of one of the flats on the nut.  The first time I laid eyes on that I knew they had an inertia problem.  I put 53,000 street miles on that belt drive and never once did the nut even think about coming loose.  It was always a huge undertaking to get it off.  The pulleys are large diameter and heavy.  When they accelerate and decelerate they simply don't want to change direction, add to that the belt tugging on it and you have a recipe for disaster.  I think I saw one post in here where a member actually welded his pulley to the output shaft.  That's desperate.


I learned a bunch from this project.  I took a chance and got lucky. It was a lot of fun and the results were good.  If it helps any of you with your Savage then I am pleased as punch. The sole reason I purchased my LS650 was to use it as a test bed.  I want to see how far I can take it and still have a pleasant and reliable scooter.

There are some apps for smartphones that do 1/4 mile runs broken down into 0-60, 330 ft, 660 ft, 1/4 mile, and top speed for that run. The one for Android is called Car Performance. The paid version gives you a countdown timer for the start, and the free version starts as soon as it senses movement. That one could be a good thing since it takes reaction time out of the equation.

 I'm going to get rid of half my clutch plates to lesson rotating mass

Just an update on my tool height.  I was about .017" too high so my bit was rubbing rather than cutting.  Found a couple of good YouTube videos.  Both show really easy ways to check for proper tool height, and I could have done it with the workpiece in place.

https://www.youtube.com/watch?v=AyOVFzCuGSs

https://www.youtube.com/watch?v=vpCu56O8AJ0

I dont know.. but as a formar race mecanics, it was my brother that did the driving/racing!
Everybody had almoste shift to a lighter flyeweel.. so he altso by one, very expensive!
It suposed to get at least a better gas respons.. it didnt, and there are resons for that!
And the reason for that is, it get faster respons whit no gear in.. whit the gear in and driving one moste count the whole e´weight of the car.. or bike!

The only good outcome is that is easyer to shift gear!!!!
And thats what its about, easy gear shifting!!!

And the drawbacks, it did perform bad at low revs, like driving it frome the depoe to starting line.. after that.. race cars supose to goe att highest revs as posibly.

Soo its about the inertia.. this bike is a thumper, I can always put it on the stand and it puffs around  anyway.

To that.. I think that enginers on Suzuki have figur it out anyway?

But if one dont ride on low to middel revs, one dont need that much of a flyweel.. one got the inertia by higher revs.

And to that, nr 2, its seems to me that the balance axcel system are heavyer then the flyweel?

One dont need that eighter on high revs, but then, one can only drive att hig revs?

Summarised, less inertia make one shift gear a lot faster/easyer, thats important on race tracks!
One dont got a better accelration on the bike/car.. becuse then the inertia  one have to move is the whole bike/car!

This bike is a low weight bike, thats good, less inertia to move around, its a thumper, gonna need some inertia in the engin to run smotly.

Sooo I have another kind of cheep proposal.. the inertia of the bike and driver is the major problem, the bike is very low weigt, nothing more to do there.. then its more about the driver, losing some pounds or kilos, gonna do more then geting a low weight flyweel?