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Holy Engine Brake Hawkman!

Old 11-03-2015, 12:03 AM
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Holy Engine Brake Hawkman!

I recently installed one of E. Marquez's Option #4 Lightened Flywheels. The single most cost effective, simple, performance enhancing modification, so far. Coupled with removal of the anti-rattle gear, addition of a 4+ ignition advancer, Yosh. slip-ons, TPS cal. and carb sync, and a finely tuned Hawk Carb Set-up.. I have a sweet running '98SH. Sorry, got a bit off track.
I've read multiple threads regarding effect of the of the lighter rotating mass. Obviously, the motor spins up considerably faster. Much more throttle sensitive. The other thing that has been mentioned is more engine braking. I'm not by any stretch of the imagination, have any knowledge of physics, Heck, I barely made it through high school (45 years ago) But, I didn't see how this would be the case as the lessened rotating flywheel mass is rotated quicker by the engine and it would seem it would have the same effect when rotated by the rear wheel/trans. This is what I felt after the flywheel change. I even switched back and forth several times between the stock and lightened FW's. Same result. I'm old and have landed on my head more than a few time so maybe the '60's have effected my thought process. I then gathered 5 riding friends varying in types of bikes normally rode, Dual Sports To one friend with considerable track racing experience. I told them I was trying some very slight gearing changes. Over a period 24 days , and a lot of free pizza, I had every one ride my SH 4 or 5 times over a set course. I changed the FW randomly without the perspective rider knowing which FW was installed. They thought it was just a tooth or 2 up or down on the rear sprocket. I had each person give feedback on acceleration and engine braking. After 23 rides, 12 with the lightened FW. Every one, with the exception of the 525cc single dual sport rider, remarked that there was less engine braking with the Lightened Flywheel!
I'm not complaining I like it. It's easier to match engine/trans speed when
down shifting and on/off throttle transitions are smoother. Any ideas?
If nothing else, I can change FW in under 5 mins.
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Old 11-03-2015, 01:03 AM
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Well,

After 2/12 years with the lightened flywheel on my bike and similar mods to yours except H C pistons and Billet H Power stacks I got the opportunity to ride a mates VTR with a standard flywheel and can definitely say that the lightened flywheel offers a lot more engine braking.

Like you I am no physics professor but my bum tells me the engine braking with a lightened flywheel is much much more than standard.

We put both bikes side by side and let the throttle off and his raced away from mine.

Crude test but very conclusive.

Lightened flywheels offer more engine braking in the real world.

I'm sure that someone will be able to explain the physics of this.

P.S we did this at 60MPH or 100KPH as we say here down under
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Old 11-03-2015, 07:05 AM
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Maybe it has to do with "flywheel effect".
Once a heavier mass is put in motion, it takes more energy (or more time) to slow it down.
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Old 11-03-2015, 10:20 AM
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No experience with a lightened but I would think the engine would rev down more easily thus engine braking would be better or quicker.
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Old 11-04-2015, 11:24 AM
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Originally Posted by CaryDG View Post
If nothing else, I can change FW in under 5 mins.
It is the effect of mass in motion decelerating at a slower rate than a lighter mass...

Can you provide a step by step description of your FW removal and installation procedure? I know what must be done and have done it on other MC engines including 2-strokes but not the VTR.

Any tips and tricks or cautions would be appreciated, including tools, parts and tools need (I have a FW puller can the cover gasket). Pics would be great too. I have case guards I think will need to be temporarily removal for access.

Another 60 something

Thx
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Old 12-07-2015, 07:23 PM
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Sorry about the delay! The VTR is relatively easy. The most noticeable difference is that it requires a single movement puller (basically a hardened bolt) whereas many FW's take a two piece puller. One piece threads into the FW and then the other threads into that piece and against the crank end.
Remove FW cover and clutch slave cylinder (for clearance) no need to disconnect the line, just the bolts. Remove FW bolt. I found the with an impact you can remove the FW bolt without a FW holder. If you don't have access to an impact you will need a strap type holder or you can just put the bike in high gear and apply the rear brake. An impact also makes it much easier to run the puller (bolt) in. Installation is just the opposite, But, you'll need to put the bike in high gear and apply the rear brake to torque the FW bolt properly. Put the case and clutch slave back on and ride!
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Old 12-08-2015, 06:04 PM
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Physics lesson:

To understand how the physics work on deceleration with a lighter flywheel,
Imagine two wheels rolling downhill, one is a car wheel and the other is a truck wheel, which one you think you will be able to stop quicker?
The heavier wheel stores more energy, (in the above case is gravity), thus you need to use more energy to stop it, or in the flywheel case inertia (mass in motion) as Skokievtr mentioned, same thing, the heavier wheel you need more energy to get it going and once it is in motion, takes longer to slow it down as it is storing bigger amount of energy due to bigger mass, Kapish?

In effect, the engine braking is the energy applied on the flywheel which stays the same! But the amount of energy it is resisting that stored in the flywheel is smaller, as such the bike decelerating quicker.

Hope that helps...

Last edited by NHSH; 12-08-2015 at 06:10 PM.
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Old 12-08-2015, 07:49 PM
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Yep, a heavier flywheel releases stored energy slower than a lighter one against the friction of the tires, wheel bearings, cam drive and valve guides and springs, rear drive chain and sprockets, transmission gears and bearings, crank and connecting rod bearings, piston and piston rings, wind drag, etc

More finely controlled throttle inputs are thus required both going up and down the RPM range. Without a slipper clutch, the rear tire will chirp and it could loose traction and come around while the front suspension compresses as weight is transferred forward putting more load on the front tire increasing traction there and also quickening steering; all recipes for disaster if you're not careful. On the other hand, one could use the weight transfer to turn-in sharper, initiate a power broadside steering, and of course accelerate faster than possible with a heavier flywheel.
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Old 12-09-2015, 11:21 AM
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It's quite simple: L=(1/2mr^2)*(v/r).
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Old 12-09-2015, 11:54 AM
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Right! Please prove the below formula with symbol definitions utilizing as an example a VTR flywheel that is 1# lighter than OEM; i.e., 6# 5/8 oz versus 7# 5/8 oz.

Originally Posted by Just_Nick View Post
It's quite simple: L=(1/2mr^2)*(v/r).
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Old 12-09-2015, 02:54 PM
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You also need to define if the radius of both flywheels are the same.
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Old 12-09-2015, 08:28 PM
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Swapping out the air in your tire for helium will produce similar results...

For adverse effects try filling the tires with water...

James
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Old 12-09-2015, 09:17 PM
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Originally Posted by thedeatons View Post
Swapping out the air in your tire for helium will produce similar results...

For adverse effects try filling the tires with water...

James
Or shaving your own weight...
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Old 12-10-2015, 11:28 AM
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Shaving your own weight wouldn't change engine braking characteristics.
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Old 12-13-2015, 07:52 PM
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Originally Posted by Just_Nick View Post
Shaving your own weight wouldn't change engine braking characteristics.
Not the engine braking characteristics, true, but it will make the braking shorter and quicker!
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Old 12-14-2015, 08:50 AM
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It might help to remember what engine braking force is coming from.

Engine braking comes from resistance of the pistons compressing air. The motor is still moving but not getting adequate fuel with the throttle closed.

It does not come from all of the weight of the parts in the motor. When your bike slows down from engine braking it is actively resisting speed, not just coasting it off, slowing down from friction loss forces.

This is where Newton's first law comes in. Objects in motion want to stay in motion. That heavy flywheel wants to stay moving. The pistons are resisting all the mass of the drivetrain and rider when engine braking. When you lighten the flywheel, you have less resistance in the system and so have more available braking force.
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Old 12-15-2015, 06:23 PM
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After all the great input, and physics aside, I've come to believe that what we were mistaking for less engine braking was that the lightened FW engine revved up quicker when blipping the throttle to match engine to tranny speeds. That coupled with the fact that all the test riders are off road riders/racers and have a tendency to feather the clutch and keep the R's up.
We did the test again with the OEM FW and the Opt. #4 lightened one, This time 4 different riders took it up to 6k RPM in 3rd gear and then just shut the throttle. There is definitely more engine braking with the lightened FW! We tried it twice each with both FW configurations. Live and learn.

Last edited by CaryDG; 12-15-2015 at 06:31 PM. Reason: added sentence
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Old 12-15-2015, 06:47 PM
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Originally Posted by 7moore7 View Post
It might help to remember what engine braking force is coming from.

Engine braking comes from resistance of the pistons compressing air. The motor is still moving but not getting adequate fuel with the throttle closed.

It does not come from all of the weight of the parts in the motor. When your bike slows down from engine braking it is actively resisting speed, not just coasting it off, slowing down from friction loss forces.

This is where Newton's first law comes in. Objects in motion want to stay in motion. That heavy flywheel wants to stay moving. The pistons are resisting all the mass of the drivetrain and rider when engine braking. When you lighten the flywheel, you have less resistance in the system and so have more available braking force.
So in reality this shows that rider weight does in fact play a factor in engine breaking in a negative light. Forward motion verses down force and load and reverse transfer through the sprockets back into the fly wheel. A heavier rider would actually cause a larger cytripical force on the fly wheel causing more mass to be over came plus the tangent force of weight moving forward. Hmmmm.

Yes this is based on beer logic right now.
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Old 12-16-2015, 11:50 PM
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Yeah, what he said! LOL
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Old 12-24-2015, 07:46 PM
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Lol
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Old 12-25-2015, 10:27 PM
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Would this be effected by out of balance ceramic muffler bearings? And, if so, to what extent?
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