why not to use a lightened stock flywheel
- Thread starter CMF_evade
- Start date
CMF_maat
» CMF Member
jeeeeeeeeeeeeezussss thats insane, imagine the damage a piece of that could do if it had have gone through and hit the driver
CMF_Yom
» CMF MemberThis could could happen to an aftermarket flywheel guys. Regardless of brand. Heck it even happens to stock, unmodified flywheels. Extremily unlucky if it does, but it can happen.
CMF_jaxx
» CMF Membermust of bin running excessive power with not the right mod's done or not done properly. hope my datrats one holds up!
CMF_evade
» CMF Memberyeah the JUN one is a complete unit..where as the lightened stock flywheels just use the ring gear around the edge..
which is what has come apart here..and through everything..ouch
too bad if it was a honda...the flywheel is pretty much inline with your crotch
which is what has come apart here..and through everything..ouch
too bad if it was a honda...the flywheel is pretty much inline with your crotch
CMF_Yom
» CMF MemberJust to get it out of the way, the ringgear (and its construction/attachment to the flywheel) has very little to do with the strength of the flywheel.
A cast flywheel CAN be safely lightened (depends 110% on the construction of the flywheel to begin with) but whether it can be safely lightened enough to notice any difference is a whole different matter - typically the 2 piece flywheels which are good to lighten (like on the micra) are already about as thin as they can be to save in manufacturing costs.
Good to point out right now that even just dropping a cast flywheel can ruin it (without damaging it visibly). I wonder how many apprentice mechanics out there have dropped flywheels and not told anyone about it?
A cast flywheel CAN be safely lightened (depends 110% on the construction of the flywheel to begin with) but whether it can be safely lightened enough to notice any difference is a whole different matter - typically the 2 piece flywheels which are good to lighten (like on the micra) are already about as thin as they can be to save in manufacturing costs.
Good to point out right now that even just dropping a cast flywheel can ruin it (without damaging it visibly). I wonder how many apprentice mechanics out there have dropped flywheels and not told anyone about it?
CMF_MicraItaly
» CMF MemberO_O oh my god....
CMF_nz_aj
» CMF MemberThere are a lot of rules about 6mm thick plates around the bell housing for fast cars on the strip. I think this was anything doing 13s for rotaries & 12s for piston cars. I think anything much faster than that was not allowed a cast flywheel.
There are plenty of cases where bits of flywheel have come through the floor/firewall of various cars.
There are plenty of cases where bits of flywheel have come through the floor/firewall of various cars.
CMF_EVLGTI
» CMF MemberHave been running a lightened standard flywheel on the GTi for a number of years. Without any issues at all.
Have gone through 3 or 4 gearbox but still the same flywheel.
I knew there was something else that needed to be done for Tech, still havent fitted the flywheel shield....
Have gone through 3 or 4 gearbox but still the same flywheel.
I knew there was something else that needed to be done for Tech, still havent fitted the flywheel shield....
CMF_LWC
» CMF MemberFrom an engineer: flywheels have a design speed in rpm and a design strength/lifetime that matches this rpm. When you lighten a stock flywheel you reduce the design strength because metal has been removed, you then go and rev the engine harder and at higher revs which overstresses what is left of the flywheel.
Eventually it will give way, not after 15-20 years but maybe only after a few months if the lightening was done poorly and introduced "stress raisers" where the machining was done.
The solution is to buy an engineered aftermarket flywheel from a business that knows what it is doing.
BTW the drag racing folks reinforce the firewall with steel plate known as a scatter shield which does what its name implies, catches the bits of flywheel that break off during a drag.......
Eventually it will give way, not after 15-20 years but maybe only after a few months if the lightening was done poorly and introduced "stress raisers" where the machining was done.
The solution is to buy an engineered aftermarket flywheel from a business that knows what it is doing.
BTW the drag racing folks reinforce the firewall with steel plate known as a scatter shield which does what its name implies, catches the bits of flywheel that break off during a drag.......
CMF_nz_aj
» CMF MemberFrom another engineer.
Flywheels are designed to have inertia. A vehicle manufacturer decides how much inertia they want, in order for power output to be smooth & the clutch easy to use. More inertia makes it harder to stall when releasing the clutch.
The cheapest way to make a flywheel is to concentrate the mass to the outside.
I think I can safely say that all standard car flywheels have more metal around the outside than what is needed for strength.
Most reputable machinists know what they are doing when it comes to lightening flywheels. They will remove metal from the outside leaving enough around the bolt holes & radiusing any concave cuts, so as not to create stress raisers.
Done correctly this will raise the strength / design rpm.
The amount that can be removed safely usually makes a very noticeable seat of the pants effect when accelerating from a stand still.
People always want more & thats when you have to go with an aftermarket or custom flywheel. Make sure you compare options thou. There can be a huge difference between the inertia of Brand X & brand Y. Also consider the inertia of different rpessure plates.
I'd go for cromoly not aluminium, by the time the aluminium flywheel has an steel insert for the mating surface, it's heavier and/or has more inertia than what can be done with cromo.
Flywheels are designed to have inertia. A vehicle manufacturer decides how much inertia they want, in order for power output to be smooth & the clutch easy to use. More inertia makes it harder to stall when releasing the clutch.
The cheapest way to make a flywheel is to concentrate the mass to the outside.
I think I can safely say that all standard car flywheels have more metal around the outside than what is needed for strength.
Most reputable machinists know what they are doing when it comes to lightening flywheels. They will remove metal from the outside leaving enough around the bolt holes & radiusing any concave cuts, so as not to create stress raisers.
Done correctly this will raise the strength / design rpm.
The amount that can be removed safely usually makes a very noticeable seat of the pants effect when accelerating from a stand still.
People always want more & thats when you have to go with an aftermarket or custom flywheel. Make sure you compare options thou. There can be a huge difference between the inertia of Brand X & brand Y. Also consider the inertia of different rpessure plates.
I'd go for cromoly not aluminium, by the time the aluminium flywheel has an steel insert for the mating surface, it's heavier and/or has more inertia than what can be done with cromo.
CMF_Yom
» CMF MemberAnd then you have 2 piece flywheels like the micras which use a steel backing plate as the 'spine' of the heavy friction surface. Std micra (1.3L) flywheels can be machined down to around 5kg with relative ease apparently and have excellent weight distribution thanks to the steel backing plate which is their support (there's ALOT of meat around the edges of the std flywheel). I personally wouldn't trust that, so thats why gtrholic had some nice chromoloy items made up by a well known machinist (Tighe Cams in QLD) which use the factory ringgear (no issues with teeth spacing so no issues with starter motor = win).
(and offtopic, but they ended up being significantly cheaper than the JUN flywheels and despite being slightly heavier on paper I honestly believe they're a better product than the JUN - especially for the price).
(and offtopic, but they ended up being significantly cheaper than the JUN flywheels and despite being slightly heavier on paper I honestly believe they're a better product than the JUN - especially for the price).
