When a manufacturer builds a car, designers optimize it for various road conditions, weather conditions, safety, a smooth ride, and fuel economy. The engine and transmission are tasked with moving the bulk of the vehicle, which can be 3,000 to 5,000 pounds, around on a daily basis. The flywheel serves as the main point of contact for the transmission, which transmits power through the drive apparatus to spin the wheels. It’s a tough job.

An OEM Mitsubishi Evo X cast-iron flywheel.

Most manufacturers build and equip their vehicles with heavy flywheels because it helps the engine operate smoothly, and enables it to retain energy at partial-throttle cruising, as well as traveling up steep grades for better fuel economy.

In a performance or racing scenario, a lightweight flywheel will cause the engine to rev up very quickly and allow it to work easier due to the reduced mass that the crankshaft has to spin. As soon as you let off the gas, the revs will drop instantly, slowing the car down. That is exactly what you would want in a road race or drag car, but in a street car it can cause surging and bucking at cruising speeds, as well as poor drivability and difficult clutch engagement.

Not all lightweight flywheels are created equal, though, and there are various weights and sizes to choose from. We reached out to Dan Jenkins of Fidanza Performance to talk about lightweight flywheels, how they’re made, the performance benefits, and Fidanza’s list of applications for the import-favoring crowd.

Types Of Flywheels And The Benefits

There are a lot of materials that can be used for manufacturing a flywheel, but the two most common types are steel and billet aluminum. Many automakers make their factory flywheels out of cast-iron, ultimately to keep costs down. Cast-iron is a very heavy, porous metal that can become brittle when exposed to high temperatures and high-stress loads. Although aftermarket cast iron and nodular iron flywheels can be purchased, they simply can’t take the stress and heat of a day at the dragstrip or racetrack, especially with a vehicle that produces substantially more power than stock.

Within these base materials you can find several types like chromoly steel or billet steel, and 6061 or 2024 aluminum,” Jenkins explained. “All of which have their own pros and cons; some materials are beneficial to road course racing, while others are better for off road. When designing a flywheel, we have to take all of this into consideration, and then the materials are chosen to work in a specific application for the optimal performance and reliability. All of our flywheels, whether they are made from aluminum or steel, are CAD engineered and CNC-machined from billet forgings.”

A billet steel Fidanza flywheel.

Steel flywheels are developed and built to be stronger than factory cast-iron units, and can even weigh the same, or even more than a factory cast unit, but are a lot more likely to hold their composure under high-stress loads, such as high RPM. Steel flywheels are designed to endure extreme stress, and not provide increased performance. It’s certainly not uncommon to see steel flywheels that are SFI-approved for race use.

As steel flywheels are one-piece, they require resurfacing every time the clutch is replaced, inevitably causing them to have a shorter service life. Heat is another challenging factor for steel flywheels because they simply don’t help heat dissipation while paired with a performance clutch, and can’t improve clutch performance or longevity. Another drawback is the ring gear teeth, and the fact that they are incorporated into the design. Any damage to the teeth will warrant replacing the flywheel with a new one.

Like steel flywheels, aluminum flywheels are designed to be stronger than OE cast-iron units. The lower weight will provide significant performance benefits in terms of faster throttle response, smoother shifting, and quicker acceleration. Easier vehicle braking is also achieved by reducing parasitic driveline losses.

A cutaway of a Fidanza single-plate clutch and flywheel assembly.

“A billet aluminum flywheel will provide a more responsive and ‘nimble’ driving experience over vehicles equipped with heavy cast-iron or steel flywheels,” Jenkins noted. “In addition, aluminum flywheels are much better at dissipating heat from your clutch, which can greatly improve clutch performance and life, whether it’s a factory-style clutch disc or a performance disc.”

Choosing a steel or billet aluminum flywheel ultimately comes down to the vehicle’s planned uses, such as drag racing, road racing, daily driving, spirited driving, etc. Over an OE cast-iron flywheel, both materials will stand up to more heat and high-stress loads, and are improvements over cast-iron OE units, depending on what you are looking for in terms of strength and performance, what type of vehicle you have, and how you use it.

Flywheel Design And How They Are Made

A lightweight aluminum Fidanza flywheel with replaceable friction surface for an Audi.

As all of Fidanza’s flywheels are CAD-engineered and precision CNC-machined, most are designed as a direct replacement for OE units, and do not require any additional modifications to be installed. Fidanza also designs its flywheels as a multi-piece unit, meaning they are completely serviceable by the consumer, or Fidanza’s in-house tech department.

With the replaceable friction surface, you never have to resurface the flywheel, giving it an almost infinite lifespan,” Jenkins explained. “Simply replace the friction plate when replacing the clutch and the flywheel is like-new again. We also use a separate starter ring gear, allowing replacement if damage were to ever occur from a failed starter or pinion gear.”

During the design process of Fidanza’s aluminum flywheels, a 40 to 60 percent reduction in weight compared to the OEM unit it’s replacing is figured into the flywheel’s construction. The reduction in weight plays a big part in delivering quicker throttle response, and freeing up horsepower that the engine is already producing, all while maintaining comfortable, civilized driving habits.

“If too much weight is removed adverse affects can happen, like higher RPM needed to begin moving the car, idle changes, and possible stalling, or even OBD sensor issues causing the dreaded check engine light,” Jenkins noted.

From left to right: The blank secured into the CNC lathe, the blank turned into the overall shape of the flywheel, and the CNC mill drilling the proper holes.

Once the flywheel prototype is real-world tested, it is ready to be produced for consumer usage, which starts with a blank of raw material in the CNC lathe, whether it is 6061 T6 aluminum, 2024 T3 aluminum, or 1045 forged billet steel. The blank is then turned to resemble the overall shape of the flywheel. Once off of the lathe, the flywheel is secured into a CNC mill where it is drilled with all of the correct holes for its application.

An exploded view of one of Fidanza’s aluminum flywheels with replaceable friction surface.

After the aluminum flywheels are finished with machining, they are cleaned up and completed by a production tech, who installs the 1050 steel friction plate with military-grade aerospace fasteners, steel stepped dowels, and a heat-treated 1050 steel ring gear. As the friction surface of the steel flywheels can be resurfaced, they don’t get a replaceable friction surface, just the heat-treated ring gear. Once completed and inspected, they are packaged and are ready for distribution.

Fidanza’s Import Applications

Fidanza has a big presence in the domestic and musclecar market, but the company also produces an incredible amount of flywheels for the import market. No matter where you are in the world, no matter what car you drive, Fidanza most likely makes a flywheel for your application. Some popular import automakers Fidanza manufactures flywheel replacements for include: Toyota, Nissan, Audi, Acura, Honda, BMW, Infiniti, Lexus, Mazda, Mitsubishi, Mini Cooper, Subaru, Volkswagen, Lotus, Porsche, and the freshly-deceased brand, Scion. There are a lot of vehicles Fidanza makes replacement and upgraded flywheels for, and you can find those in their applications catalog.

What type of flywheel is your best bet? We asked Jenkins about that popular topic, and he told us, “This is the age-old question that does not have one definitive answer. They all have their rightful place, whether in racing, or street use. You can search all over and find differing opinions on which to use; aluminum flywheels have many benefits that steel does not offer, just as steel has benefits that aluminum can’t offer. In most instances, the two are interchangeable without issue, but the choice between steel and aluminum performance flywheels is mainly a function of the vehicle’s planned uses and driver preferences.”

So, when choosing a flywheel, take into account how much power and torque the engine produces, and how the vehicle will be used. Either type of flywheel is a great improvement over cast-iron OE flywheels, it just comes down to user preference. The bottom line is the selection of a lightweight aluminum flywheel or a billet steel flywheel is a matter of performance that should be taken seriously.