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Doing a clutch job is also the perfect time to do a flywheel swap. Thanks to MIQ reader DaGou, I learned that the AP1 flywheel is significantly lighter than the AP2 flywheel. The AP1 weighs in around 14lbs versus the 22lbs of the AP2 flywheel. The reduction in mass reduces the rotational inertia meaning the flywheel will accelerate faster.
Rotational inertia is a function of mass and the radius of the mass from the axis of rotation. If we assume the mass was removed from the same radius, we can say the AP1 flywheel has about 2/3 the inertia of the AP1 flywheel. Torque, inertia, and angular acceleration are related to each other by the equation:
torque = inertia X angular acceleration.
Therefore, the same torque input (the engine crank output hasn’t changed) will result in the AP1 flywheel accelerating ~60% faster (22/14= ~1.57) than the AP2. Of course, the clutch is bolted to the flywheel and I forgot to measure how much the OEM and Centerforce clutches weighed. To make the math simple, I’ll assume they weigh 14lbs like the AP1 flywheel. So the total mass of the AP1 flywheel/clutch combo is about 28lbs vs. 36lbs of the AP2 flywheel/clutch combo. So the new combo has 7/9th the mass of the old combo and therefore 7/9th the rotational inertia based on my previously stated assumptions. So, the new combo should accelerate about 30% faster than the old combo (9/7 = ~ 1.286).
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| The AP1 flywheel makes for a nice budget upgrade to the AP2 flywheel. I knew the guys over at Evasive Motorsports deal with S2000s all day long, so I gave them a call. They happened to have a used AP1 flywheel that they had already resurfaced. Score! Check out the flywheels in the section between the friction surface and the bolt holes. You can see the AP2 flywheel has a lot of added mass in this section. |
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| Looking at the other side of the flywheels, you can again see how much more mass there is on the AP2 flywheel. On this side, the mass is removed further away from the centerline which has a greater impact on reducing the rotational inertia. Make sure to get a new pilot bearing when doing the flywheel. I used a socket to put on top of the bearing to tap it into the flywheel. |
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| Here is the Centerforce Dual Friction clutch installed along with the AP1 flywheel and new throwout bearing. I’ve done most of the work on the S2k up to this point, but I got smart this time and took the car to Howard at Technosquare. Howard has done a couple S2ks before and didn’t even need to look at the factory service manual. |
So just how much more responsive is the new and lighter flywheel/clutch combo compared to stock? The Hondata KPro comes to the rescue again with its datalogging ability.
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| I forgot to do a test specifically to measure the engine responsiveness before the clutch/flywheel swap, but I dug through some of my old datalogs to find suitable data. The old data on the left shows a 5th gear to 3rd gear rev-matched downshift, so I replicated that with the new clutch/flywheel combination on the right. |
2 comments
Came to this article as i was interested to see you’re confirmation of lightweight flywheel performance, i know it for myself after i did it and wow what a world of difference no other mod can replicate.
Interesting you noted noise introduced by the engine mounts. When i did mine in my drift spec BMW 328I i also noted this after doing engine/box/diff mounts all at once to fairly stiff aftermarket options, i thought i was off my rocker a little thinking the car under hard load sounded better but quickly confirmed this, I also enjoyed the mechanical feel of gearbox/diff spinning up you can now feel through your butt, real racecar stuff!
The engine mounts where one of the best mods for adding ‘feel’ to the car. Once I bumped the idle speed up 🙂 Love the improved shifter feel and the extra noise.