Why lightened flywheel

The main advantage to a lower flywheel mass on race cars is that the reduced mass allows the engine to rev more freely. The overall weight loss to the car is really not the key thing, it's letting the engine vary RPM really quickly. Being able to change RPM quickly can mean faster shifts, getting to a power band more quickly, etc, etc.

It also makes the car much more twitchy to drive since it doesn't like low RPM very much. At low RPM the lower mass of the flywheel means you need to use the throttle to keep the RPM above where the flywheel isn't going to carry things around as well. For a race car that's not a big deal. For the family driver with the manual transmission, it's a big problem. To add a bit especially for cars , in a race car you often want to be dropping from something like rpm to maybe rpm or an even higher band, depending on the engine in a split second to make an upshift.

Especially at higher engine speed, that's a lot of energy to bleed and goes as a function of the weight of the flywheel. The lighter the flywheel, as soon as you hit the clutch, the faster the engine speed will drop. This is a double-edged sword. Not only does it let you shift faster, you must shift faster - and more precisely. The time between clutch and shift at ideal rev-match is reduced, and the window of opportunity to make a perfect shift is also reduced.

Your revs won't just hang around, slowly bobbling down giving you lots of time to fuss with the shift lever - they sink like a stone and you must make the shift before they drop too low or else you get a rude shock when you let the clutch out again.

Same deal for downshifts - a heel-toe gives you a very fast RPM bump but, again, you have to make the shift in the brief window that presents itself.

Clutch springs are usually stiffer on racing clutches as well, so badly timed shifts are even harder on your vehicle - not only will a sloppy shift kill your race time, it will hurt your car as well. The low weight of a racing flywheel also makes moving off from a stop harder. When you're racing, you only do this once per race - sometimes not at all if it's a rolling start. When you're commuting you do this all day long. A heavier flywheel carries much more momentum - when you feather out the clutch from a stop, this momentum helps to keep the engine running at a steady RPM as you add load and gives you more latitude in your throttle control to keep the car going and setting off smoothly.

With a racing flywheel, you get no help here - as you feather out the clutch from a stop the engine will bog down rapidly and stall if you don't add fuel to keep the revs up.

But because the flywheel is so light, adding just a bit of fuel sends the engine racing off to high RPM if you jump the gun before the clutch starts to engage. This whole procedure is much more sensitive with a light flywheel and a stiff, grabby clutch. Daily driving like this would be a nightmare - stop-and-go traffic would be a full body workout and mental exercise in concentration. If they opt for a lighter flywheel, the idle RPM will have to be higher in order to maintain engine stability, which translates to more fuel consumption and lower fuel economy.

For an average vehicle where performance isn't a priority, it makes little business sense to go down this route. More often than not, folks who install a lighter flywheel in the name of performance have to raise their idle speed in order to keep the engine running. Not only does it conserve momentum, but it also dampens out unwanted vibrations, which reduces drivetrain stress.

It also helps the engine start in the first place. The engine flywheel is ringed with gear teeth that mesh with the starter motor, ItStillRuns reports.

When you turn on the ignition, the starter motor uses the flywheel to rotate the pistons and start the combustion cycle. Having a heavier engine flywheel is sometimes beneficial, ItStillRuns reports. If your vehicle is working under heavy loads, say, pulling a trailer, a heavy flywheel prevents it from stalling.

But if the goal is performance, extra weight, especially rotating extra weight, has to be removed. Fitting a lighter engine flywheel has some drawbacks. If you decide to go down the lightening route make absolutely sure the person who does it knows what they're doing because you are literally trusting them with your life. Wildoliver and GreenV8s' advice is good. Personally, I'm not a fan of lightened flywheels, especially for cars that are likely to see road use; they don't do anything for the engine's low speed and idle manners, they can make the gearchange more difficult on synchro boxes, and having seen the results of a lightened Cast Iron flywheel letting go on a friend's hillclimb Mini, there's no way on earth I'd want to place any part of my anatomy in the firing line.

Fortunately it exploded forwards in his case, but it punched a nice big hole clean out though the clutch housing, bonnet and front end of the car. If it's a pure track car, then maybe the benefits would outweigh the disadvantages, but it would still be fairly well down my list of priorities when it comes to spending money on tuning.

If you feel you must get a lightweight note: not lightened! As Wildoliver says, it does depend a lot on the car, but your tuner is right - particularly on smaller engined less torquey cars with very sticky rubber, such as tend to be used in hillclimbs, there's a real chance it will bog down badly off the line. One exception to the above advice is that if you intend to fit a dog engagement gearbox, you'd be well advised to fit a lightweight flywheel to give the dogs an easier life. Hi All, Many thanks for the advice I really appreciate it.

The car in question is my E28 Mi track car. It has been fully prepared full 8 point weld in cage, brakes uprated, fully adjustable platform suspension etc and now tips the scales at circa kgs. The engine has been left alone, however the clutch is now on the way out, so I thought it best to do the flywheel at the same time I'm unsure as to what the current flywheel weighs, but I'm sure it is heavy!

Given the additional info, does this change anything regarding your answers? Cheers all, DTC. Something that started out life as a big barge with a very big engine would suit a heavy lightening of the flywheel if the engine was in something light, or the car had been stripped On a car with relatively tall gearing, a biggish engine, I see little point in bothering with a lightened flywheel, unless a particular clutch happens to come with one anyway. Ive never went out of my way to have a lightened flywheel, and probably never will.

RT posts months. Flywheel weight doesn't affect torque. It only affects engine inertia. There are other benefits, too. For street applications where you might use the car as a daily driver in addition to HPDE, there is such a thing as too light. In addition to harsh engagement and the aforementioned vibration, flywheels that are too light can trigger check engine lights, hamper a smooth idle or create a situation where excessive rpm is needed to get the car to accelerate.

The material we have for our friction surface of the flywheel is designed to mate up with anything from an organic OEM style clutch to a ceramic to a Kevlar to a sintered iron.

All of those will work with no problem. Fidanza CNC-mills its flywheels from T6 aluminum with heat-treated and flattened steel for the friction surface. The friction surface can be replaced by unbolting it from the aluminum portion and bolting on a new one with new self-locking fasteners.

Before putting them on the market, Fidanza sends out all its products for SFI certification.