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Besides having a broken hub, the stock clutch disc was very worn and the rivets were starting to wear into the flywheel and pressure ring. You can see that the ACT disc has a much stronger disc hub assembly with additional material around the hub button and stiffer dual springs. The hub button itself is much more substantial and the stiffer springs will prevent the hub from internally bottoming out putting stress on the spring carrier part of the hub. This is probably what made the stock hub fail.
The ACT pressure plate has a thicker and stronger cover than stock and a much stiffer diaphragm spring for greater clamp load. 
The ACT XACT Prolite flywheel is made of strong forged chromoly which is almost 2X stronger than the stock flywheel's cast iron material. You can see how the ACT flywheel on the right is extensively machined for reduced weight. 
The ACT flywheel was bolted in place. The flywheel bolts had a small amount of Loctite Red applied to them before they were torqued down. 
Using the provided clutch alignment tool, the clutch disc and new Honda OE throwout bearing were installed and the pressure plate bolted down.
The transmission was bolted back to the engine, engine raised into place and everything reinstalled. The S2K is a lot easier to do a clutch job on than your typical FWD car. Once installed we evaluated the ACT HD clutch and flywheel. The clutch engages in normal driving very nicely. It is very smooth and engages without chatter. There is no perceptible increase in gear rattle as often tends to happen with lightweight flywheels. The clutch also grabs well at higher throttle and RPM levels.
The acceleration is improved due to the light flywheel but it is not a huge difference because the AP1 flywheel is pretty light to begin with. We figure on an AP2 with a much heavier flywheel, the difference would be much greater.
Due to the light flywheel, shifting is improved and rev matching on downshifts is a lot easier. The XACT Prolite flywheel is pleasant to drive and very streetable even though it is sold as a race part. ACT also has a heavier flywheel available, but we feel that it is ok to go straight to the lighter model even if the car is a daily driver.
The only slight negative issue we noted is that the clutch pedal effort is pretty noticeably increased over the clutch that was in the car. That clutch was a no name aftermarket stock replacement clutch so who knows what its rating was, but the ACT clutch pedal is about 50% stiffer. Normally on other cars we have tested with this same clutch combo, the clutch pedal effort was marginally changed.
Perhaps this is because this clutch has 39% more clamping force when typically the ACT HD clutch has a 20-25% increase in clamping load. Perhaps the clutch that was in the car was fatigued or speced on the light side. The clutch pedal is firm, but not overly stiff for daily driving, it's just stiffer than what we expected.
Overall the ACT HD clutch and XACT Prolite lightweight flywheel are a great upgrade for those who have an S2K with moderate power increases that are daily driven. The HD clutch is easily up to the diametrically opposite tasks of hard track driving and being smooth and comfortable on the ride home. We can honesty recommend this combo any day.
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6 comments
Are the other racing clutches for the Honda S2000 not streetable or not as desirable? I want to buy one of the most effective clutches for fast shifting and a somewhat small amount of power and torque. I strive on building a 300 horsepower all motor F20C through you guys in the near future, but I want to replace my clutch and flywheel now as it appears like it is about to go out. I don’t think I will need a clutch for massive amounts of power if I only plan of building a naturally aspirated motor. I would like to achieve my goal of 300 horsepower without stroking out the engine. I would prefer to raise the RPMs if necessary to achieve my goal. I was very intrigued by your video about the 320 horsepower K20 engine running on California 91 octane. From my research both engines are very similar in design. Currently my S2000 has a 12-point welded in roll cage with OMP racing bucket seats and 6-point harnesses. As funny as it may sound, I daily the car to the University of Arkansas and occasionally track it at Hallett in Oklahoma. However, I am originally from San Diego, California. Please tell me what you guys think when it comes to clutches and whether or not an engine build that I am describing interests you guys in the future. I reached out to you guys a few days ago on Instagram. My Instagram handle is Instaboone_ .
This clutch is fine at a good price point for that kind of use.
Thanks Mike! I noticed that ACT also makes a 4-puck and 6-puck clutch for the Honda S2000. Do you think a 6-puck clutch is too aggressive for both track and street use? I also noticed that when you guys replaced Vince’s clutch with the ACT clutch you guys opted for the OEM Honda bearings. Do you recommend that I do the same and stick with both the OEM Honda pilot and release bearings or should I go with ACT’s bearings? Is ACT your favorite brand of clutch for the Honda S2000? Thank you so much for helping me out. You guys are at the top of my list for rebuilding my engine for more naturally aspirated power!
Generally, I recommend using the least aggressive clutch that will do the job, it’s easier on the rest of the driveline.
Okay great! I will stay away from a puck clutch. Do you recommend that I do the same and stick with both the OEM Honda pilot and release bearings or should I go with ACT’s bearings?
Yes only do that when you need it. I am a big fan of OEM parts but the stuff that comes in the kit is fine.