A lot has been made of the performance advantage of an aftermarket flywheel.  Nothing has been said about the fact that the flywheel provides 50% of the friction surface to which the disc mates and consequently half the holding power of the clutch system.  For maximum clutch performance, that surface must have maximum compatibility with the disc friction material for smooth engagement and to take advantage of the increased coefficient of friction of a high performance clutch disc.  Without this compatibility, the power or torque capacity of the entire clutch system is seriously compromised.

For maximum disc compatibility we need three elements in the flywheel:  A proper friction surface finish, a perfectly flat friction surface, and a friction surface parallel to the crankshaft flange.  These three elements are achieved by surface grinding to the proper RMS finish parallel to the crankshaft flange.  Without these elements, you are giving up the features that get maximum controlled power to the drive wheels.

The following photos show the correct surface finish on a Ram flywheel, the less desirable finish on an oem type flywheel, and finally an unacceptable finish (no finish whatsoever) on a popular aftermarket flywheel.

 Surface ground RAM flywheel

OEM Factory machined finish

Aftermarket flywheel, no finish, bare metal

Heat shield flatness on an unfinished flywheel

Unfinished insert after touching on our grinder. Notice that the grind only hits the outer edge of the insert. This is flat?

Of special note is the uneven (Not flat) friction surface of the unfinished aftermarket flywheel that we find when we are grinding this flywheel to the correct finish.  How is it possible to get maximum performance from your clutch if it is installed on the slippery, uneven surface shown here?  Honestly, it’s not possible.

Flywheel balance is critical for maximum power output and engine durability

The second big issue with your flywheel is balance.  Approximately one out of twenty flywheels we produce balances out to our specification of 1/2 ounce inch maximum imbalance with no balance drilling required.  The other nineteen are going to have drilled areas to bring them into balance.

So, if 95% of all flywheels require the balance drilling (See photo), the odds are pretty good that whatever flywheel you purchase should have some drilling.  Take a look at the flywheel you are buying. Few competitors have the capability to balance to the 1/2 ounce inch specification and some of them don’t even manufacture their own flywheels or have any in house balancing capability.  One manufacturer is honest enough to state their flywheels are ‘rough balanced’ (Which means not balanced) and it is your responsibility solve that problem.  Strangely, these are the highest priced flywheels on the market.

The balance situation gets more interesting when the flywheel must be balanced to an external balance specification. External balancing requires putting a specified ounce inch imbalancewithin a one-degree radial on the flywheel.  This is nearly an impossible task without some pretty sophisticated and expensive balancing equipment.  We can show you our balancing equipment.  Most others can’t.

If your flywheel manufacturer or non-manufacturer supplier does not have the precision machine tools, precision grinding, precision balancing, and complete control of the manufacturing process in house, why would you consider purchasing their product?

Most flywheels require some balance drilling.

Flywheel Design and Materials

Performance manufacturers participate in the Safety Foundation Inc. (SFI) certification program.  SFI certification is required by most racing organizations and tracks for racing components for vehicles running 11.99 or faster before you are allowed to participate. SFI dictates the type material and mechanical properties minimums required to meet the specification and the manufacturer must submit product samples for testing in order to qualify for SFI product certification.

What SFI material specifications do not take into consideration, and many manufacturers do not know, is how the product is actually used and the abuse it must withstand under actual racing conditions. 

Aluminum flywheels typically have a steel insert for the friction surface. This insert must be substantial enough to handle the heat from clutch slippage (Intended or not).  Some manufacturers use inserts as thin as 1/8 inch. That just won’t take enough heat without distorting.  RAM flywheels have a 0.235″ thick insert on flywheels for 8 cylinder engines and 0.180″ for Sport Compact flywheels.  This provides adequate mass to take the heat from racing and enough thickness to allow resurfacing as necessary without replacing the insert.  Without a thick enough insert you can’t get the performance or service life you want from your clutch system.

Thicker RAM flywheel insert

Competitor’s thin flywheel insert

The Flywheel Buyer’s Checklist

Insist on a SFI certified flywheel.

Be sure the flywheel has a 0.225″ minimum thickness insert if aluminum. (Sport Compact 0.175″ minimum.)

Be absolutely certain the flywheel is surface ground perfectly flat and parallel to the crankshaft flange surface.

Insist on certification from the manufacturer that the flywheel is dynamically balanced to within 1/2 ounce inch minimum of specification.

Ask if the manufacturer makes the flywheel in house and has complete control of the manufacturing process.

Resist the temptation to buy a bargain flywheel. The above features will be absent.