Flywheel mod

[Rizzo97]

"The lighter flywheel: has more braking ( withouth pulling in the clutch ) " engine braking?

 

[Rizzo97]

Posting funny photos donsnt make you right

 

[SwapperMX]

I already know that you can't argue with idiots, they drag you down to their level, and beat you with experience !!

I already know that I am right, and that you are wrong !!! But just for your sake, go and google less flywheel weight results in less engine braking, and see what you find !!

 

[Rizzo97]

Sounds to me ( reading some of the articles I just googled like u suggested ) light flywheel = perfect for a good rider and = sh** for someone who rides like a grandma.?

 

[Rizzo97]

"It can be said " that there is more engine braking ... Sounds Lagit haha

 

[gottagetacheaperhobby]

No it requires the brakes to use less force to stop, as there is not as much flywheel weight to slow down. That does not equal better engine braking, merely better over all braking distance. If you read the whole article it explains it will be harder to get off the line (less torque). You also have to be very careful adapting information written for a twin cylinder to a single. The daytona style outer rotors are as light as you want to go on a single unless motarding. Our arguement is two things, 1. Your mod would of struggled to have taken enough weight out of a stock flywheel to be noticed, and 2. If you did lighten your flywheel enough to make a performance difference, you failed to lighten your slinger hence creating a un balanced engine.

 

[Rizzo97]

"our" mate.. Your the olnly one making any sence on this thread?

 

[Rizzo97]

And I didn't know there was a oil slinger in a lifan 125? Is there ?

 

[SwapperMX]

Wow, keep going Rizzo, you already look like a clown !!

Come race the Sinister 50's race at Lytton in a couple of weeks and show everyone how fast you are !!

 

[GooseMan]

Well this thread is great, I love a good debate, Ive had a change of mind, I think Rizzo is right though.

The piston can both make and absorb energy, the flywheel weight will only vary the rate at which the rpm increases or decreases. So if you had two idecntical bikes but with different weight flywheels traveling in say 2nd gear at 4000rpm and both rolled the throttle off the heavier flywheel bike's piston will have to absorb the energy of the extra weight, where as the other bike will have less flywheel inertia (energy) to absorb therefore braking will be more effective. Im not talking a huge difference between the two, almost un-noticable.

Newtons Law comes into play here, An object at rest will remain at rest unless acted upon by another force just as a object in motion will remain in motion unless acted upon by an opposing force.


The object being in this case the flywheel, if it is heavier it will have more inertia than the lighter one and will require a larger opposing a force to slow it down. A piston will only absorb so much energy at a time, so a certain amount of absorption will be used to slow the flywheel down leaving less energy absorption to slow the bike down.

Trucks use the same principle, the exhaust brake shuts a flap in the exhaust so that the piston can absorb more energy. It basically turns the engine into a compressor. The act of compressing the air in the chamber is where the braking effect takes place.

 

[timeeh]

I've had both, and I can pretty safetly say that the lighter fly decreases engine braking, even if it defies physics... That debate I won't get into.

 

[GooseMan]

Well that is weird, I wanna know why though, it interesting.

 

[8r3nd0]

My head hurts...

 

[my67xr]

ok so a lighter flywheel will rev quicker

picture yourself riding along at wot in top gear on a standard flywheel bike.
let go of the throttle and the bike will start slowing down straight away

on a bike with a lightened flywheel, doing the same thing as above, let go of the throttle
the bike wont slow down as quick will it ?
that's because the lighter flywheel can spin easier due to having less mass


i see Rizzo still hasn't put any pics up yet too ?
and Rizzo how much does your lightened flywheel actually weigh now please ?

unless you have marked out the holes with exact spacing around the flywheel it will be way out of balance.
these unbalanced harmonics will cause extra stress through out your engine.
it could easily fracture and break the crankshaft, or a lot of other components

 

[GooseMan]

That's true, it will spin easier but it is not the flywheel doing the braking, it is the act of compressing air.

So if your right, then hypothetically if the flywheel weighed 20kg then it would have extremely good engine breaking?

By the way don't think that I think I'm right your wrong, I'll be happy if you prove me wrong....

 

[my67xr]

Wikipedia says-
The term 'engine braking' refers to the braking effect caused by the closed-throttle partial-vacuum in petrol (gasoline) engines when the accelerator pedal is released. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from the vacuum.

When the throttle is closed, the air flow to the intake manifold is greatly restricted. The concept can be illustrated by the amount of effort required to blow/suck through a thin tube vs. a wider one. It is the work the engine has to do against this restricted air flow that provides the braking effect

 

[GooseMan]

That's interesting, makes sense.

 

[jay160cc]

I have never owned a dirt bike, or any motorcycle thats had a lightened flywheel, I have how ever owned 3 cars.
The car I will use was my 1997 XH falcon Turbo. I installed a 20% flywheel (20% of standard weight), about 4.5kg.
It was nearly impossible to drive around town. It increased lag aswell, I ended up swapping out cams and raising my rev limiter to compensate. When the engine did come on boost though HOLY **** HANG THE **** ON. let the peddle go at the end of the straight and it would engine break so aggressively, almost like slamming the brakes on.
Around the street it was jerky and inconsistent and a real dog to drive. If your changing lanes and apply small amount of peddle it would kangaroo hop up to speed etc, let go of peddle to return to speed limit and the engine breaking would pull 10km/h off my speed in a matter of nothing.

My point is, with my EXPERIENCE and even common sense, tells me that a lighter flywheel will indeed increase engine breaking. And acceleration for that matter BUT will absolutely ROB the engine of tourque and consistency.

 

[SwapperMX]

I may have been pretty one sided with my argument, but am going off personal experience. Having ridden two strokes for a lot of years, which pretty much have zero engine braking. My last 250 two stroke that I raced, I played around a lot with flywheel weights, mainly to help smoothen out the bottom end power and aid in gaining traction on hardpack tracks, which was crucial when racing against four strokes. The heaviest flywheel that I ran gave the bike noticeably more engine braking compared with the standard flywheel weight. While this became a heated topic, the differences are going to be pretty minimal on small capacity four stroke motors.

 

[timeeh]

And by the look of it perhaps it all depends on what that flywheel is hooked too, i.e engine size, comp ratio, gear box ect.... I found with mine it was only noticeable when rolling down hills, back off with the original full size fly and the bike would slow a fair bit, with the lightened version it now rolls away. This might be a question for the ages