Lightweight B Series Flywheels

Published: November 18, 2015

One of the goals I had for my Civic was to have the lightest possible flywheel/clutch assemby. Honda Challenge rules which the car is built to require using a flywheel that can mate with an OEM clutch and a clutch that can mate with an OEM flywheel; this excludes multi-disc clutches as well as super singles. I was left with OEM dimensioned clutches and flywheels.

Comptech

The absolute lightest B series flywheel I have read about was a Comptech one, at about 6.5 lbs. This flywheel is discontinued though and I have not found one advertised for sale anywhere.

Clutch Masters

My Integra came with an old Clutch Masters aluminum flywheel attached to the engine. This flywheel weighed in at 6.9-7.4 lbs depending on when I measured it (on the same scale; where the 0.5 lbs difference came from I don't know).

This flywheel apparently was manufactured by Fidanza and sold by Clutch Masters. It has the Clutch Masters logo etched on it. This flywheel is discontinued as well; the current Clutch Masters aluminum flywheel has a listed weight of 9 lbs.

Another consequence of this flywheel being old and discontinued is that Clutch Masters friction inserts do not fit it, as the current inserts are thicker than the one originally on the flywheel. Clutch Masters told me I needed to send the flywheel to them to have it machined to accept the thicker current inserts.

However, since the flywheel was originally made by Fidanza, the current Fidanza friction insert for B series flywheel (flywheel part number 191681, insert part number 228751) does fit the Clutch Masters flywheel. To boot, the Fidanza insert is half the price of the Clutch Masters one as of this writing.

Fidanza

Fidanza aluminum flywheel for B series engines (part number 191681) was advertised at 7.5 lbs when I started researching flywheels. However, the flywheel I received weighed in at 7.9 lbs, or about 0.5 lbs heavier than the Clutch Masters flywheel that then measured 7.4 lbs. I subsequently received another Fidanza flywheel and this time this flywheel measured 7.5 lbs, however weight of my Clutch Masters flywheel dropped to 6.9 lbs on the same scale at the same measurement time - the Clutch Masters flywheel continued being about 0.5 lbs lighter than the Fidanza flywheel. This is when I decided to get a Fidanza insert for the Clutch Masters flywheel.

Clutches

My weight reduction efforts did not stop at the flywheel - I was also looking for the lightest clutch assembly possible. On one hand the clutch is disconnected from the flywheel when the shift happens, hence clutch weight should not matter. In practice though I often do not fully depress the clutch during shifts, hence clutch weight would affect the speed with which RPMs drop. On the other hand, when the vehicle is accelerating the clutch is attached to the driveline and having a lighter clutch should help with acceleration.

Unfortunately weight for clutch kits is either not quoted at all, quoted at roughly the same numbers as OEM clutch kit, or quoted only with packaging which is pretty useless.

What I have found out was that Clutch Masters clutch kits with pads weigh about 1 lb less than clutch kits with a full circle of friction surface, and clutch kits with unsprung hubs weigh about 1 lbs less than clutch kits with sprung hubs. In practice this means that an unsprung Stage 5 clutch kit is about 2 lbs lighter than a sprung Stage 3 clutch kit.

I went with an unsprung Stage 5 Clutch Masters clutch as a result of this. It has a crazy torque rating and is supposed to be an on/off switch, but my Miata's twin disc clutch is also an on/off switch and I kind of like it that way.