Debunking the Myth of Flywheel Selection

RAM Clutches flywheels

In our last post we discussed selecting the proper clutch for your application based on load factors the clutch will experience.  Today we tackle the dos and don’ts of selecting the correct flywheel for your application.

Have you ever heard this line before?  ‘Put in a lighter flywheel and you will make more horsepower.’  Some manufacturers will tell you this, and it is simply false.  Heck, I once had a customer who was told a light flywheel would ‘increase his gas mileage!’  Is it possible for a lighter flywheel to create quicker engine acceleration? It can, depending on the gearing of the car.  Will it allow the car to decelerate quicker? Absolutely. This is why circle track and autocross racers want to use the lightest possible flywheel and clutch combination for their vehicle. It allows the car to drive deeper into the turns and have the RPM drop quicker as they let off the throttle. The engine can then accelerate back into the peak range quicker out of the turn.

For your street driven car, flywheel selection is critical to the driveability of your vehicle. The job of the flywheel is to transmit inertia to help get the car moving; be it pulling away from a stop sign, or leaving the starting line at the drag strip.  The proper flywheel weight, in conjunction with the correct gearing, will optimize your driving experience. Other load factors discussed in “It's all about the load, silly!” will also affect this, such as vehicle weight.

In general, we recommend steel flywheels for street driven cars.  This is due to the typical gearing of these vehicles. It’s important to effectively get the car rolling with the minimal amount of clutch slippage. This enhances the driving experience as well as minimizes clutch wear. It also reduces chatter with more aggressive clutch systems.  Another benefit of heavier flywheels is low-speed drivability. If you have ever driven along at slow speeds and the car started ‘bucking’ or ‘jumping’ as the RPM dropped too low, a lighter flywheel will make this worse. A heavier flywheel will make for much smoother driving at low speed due to the mass of the flywheel rotation.  Regularly driven street cars with large cams are the biggest beneficiaries of this.

Where you do you draw the line in multi-purpose cars?  I look hard at the gearing, both low gear and rear gear, as well as the drive ratio.  For instance, an optimally geared car with a 4.10 rear and a 2.89 low gear will produce a ratio of 11.89 (4.10 x 2.89 = 11.89).  A number in the neighborhood of 12:1 will make for a very friendly combination that can stand to run a little lighter flywheel combination.  Take that same car with a 3.55 and a 2.49 low gear, as many older muscle cars may have, and your ratio is 8.83:1. This will require much more flywheel weight to drive nicely and prevent the clutch from slipping as your vehicle gets moving.  In general, we look for a minimum of 10:1 in this area.

For all-out competition we will evaluate the load factors discussed in the previous article and develop a recommendation that is optimal for your specific vehicle.  I invite you to use our Email Tech Help form for suggestions tailored to whatever combination vehicle you are building.