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flexplate or flywheel for your car

Choosing an Aluminum Versus Steel Flexplate or Flywheel for a Car

Which is the best choice for your build?

When installing a Flywheel or Flexplate in a car, you have a decision to make, Steel or Aluminum? Both have benefits and drawbacks depending on your performance needs.

What is a Flywheel?

G Force aluminum Flywheel

The purpose of a Flywheel is to permit transition of power from the engine to the transmission through a manually engaged clutch mechanism. The weight of the Flywheel is a key factor when combined with the horsepower and torque capabilities of an engine, in determining the desired level of drivability and performance.

Three Functions of a Flywheel

  1. Sustain inertia to support the motor rotation and deliver a more reliable delivery of torque while the engine is running
  2. Make available a ring gear to engage the starter motor
  3. Present a driving friction surface for the friction disc

Scenarios for choosing a Steel versus an Aluminum Flywheel

Steel Flywheels are used when additional torque is needed for street driving or drag racing cars. Rotating inertia from heavy Flywheels move the car better from a stop while keeping your idle smooth and making it easier to shift gears while keeping the RPMs from dropping too fast. A sudden drop in RPMs will stall out the engine.

Aluminum lets your RPMs climb fast and fall fast but doesn’t start the car moving from a complete stop as quickly as a heavier metal like steel. On the other hand, aluminum Flywheels work better when you’re already moving instead of taking off from a dead stop. Therefore, aluminum is a much better choice for Circle Track Racing, Autocross, and Road Racing or anytime you need your RPMs to accelerate quickly out of the turn or drop rapidly to take a sharp turn.

The best example for picturing this is to think about Formula -1 cars, which use a very light, four-pound Flywheel. A Formula - 1 gains speed very quickly and takes turns at high speed but needs to be pushed out from a pit-stops.

However, some high horsepower and torque drag racing vehicles run aluminum Flywheels because they do not need rotating inertia to help leave from stops. For these cars, their engine’s 600+ horsepower and high torque do this very easily.

So, most steel Flywheels are used for street driving, and hard drag strip launches, while most aluminum Flywheels are used for Road Racing, Autocross, and high horsepower and torque Drag Racing cars.

Flexplate vs. Flywheel

What is a Flexplate?

G Force Cummins Flexplate
A Flexplate is used in conjunction with automatic transmissions and is typically much thinner and lighter than its flywheel counterpart used in manual transmissions. The Flexplate also serves to transmit power from the engine to the transmission but is used in conjunction with a torque converter. Whereas the weight of a manual transmission flywheel is key in matching to the engine’s horsepower and torque capabilities, it is the stall speed of the torque converter that is key in matching to the engine strength ratings with automatic transmissions.


A Flexplate is engaged by the starter and physically spins the engine during cranking. It’s a metal disk that bolts between the torque converter and crankshaft and has a ring of teeth interlock with the starter. Plus, the Flexplate joins the crankshaft to the torque converter.

Factor in SFI Certification

You may notice that some Flywheels and Flexplates are SFI approved. This means they have been certified safe for racing. SFI certified Flywheels and Flexplates have been engineered and tested to meet specific safety requirements established by the SFI Foundation. Many of the Flywheels offered by G Force are SFI approved.

Our Flywheels fit a variety of Make, Models, and Years. You can check out our Flywheel Collection. SFI certification is indicated clearly in the description of the part.

G Force Flywheels

G Force offers three Flexplates for Cummins swaps. They can be purchased individually—2007.5-2013 6.7L Cummins Flexplate | GF-C2BFP, 1989-2006 5.9L Cummins Flexplate | GF-C1FP, and 1994-2007 5.9L Cummins Flexplate | GF-C1BFP, or as part of a transmission adapter swap kit. Other transmission adapter swap kits, which include our Flywheels, can be found in our Swap Kit Collection.

Flywheel Weight Matters

When installing Flywheels or Flexplates, the choice between steel and aluminum depends on the type of performance you’re looking for from your vehicle. For street driving and drag racing, steel provides the heavier Flywheel needed for moving the car quickly from a dead stop.

On the other hand, an aluminum Flywheel or Flexplate is ideal for Road Racing, Autocross, or Circle Track Racing. It’s best anytime you need RPMs for quick acceleration or a fast drop in RPMs for taking a sharp turn. Aluminum handles rapid rises and drops in RPMs better than their heavier steel counterparts, but the lighter weight aluminum doesn’t perform as well from a complete stop.

In the end, the choice between an aluminum versus a steel Flexplate or Flywheel comes down to the performance you need from you car. Whether you're looking for a fast start from a complete stop or speed and handling at the turns your choice of impacts your results.


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