Xeon

So how come the AP2 has a heavier flywheel then the ap1

Slowcrash_101

It lowers engine vibration, it stores more energy so it makes taking off from a stop easier, and it makes staying in vtec in the low gears easier as the engine response is dulled, so revs don't drop as fast.

Soviet

https://www.s2ki.com/s2000/topic/732...ywheel-weight/

At least I refrained from linking you a lmgtfy link.

Car Analogy

Note the Euro cars that kept the ap1 motor, even as they got the other ap2 chassis upgrades, did not get the heavier flywheel. The ap2 motor does not have the same vtec rpm range as ap1 (6-8 compared to 6-9). To try and keep rpms in vtec between shifts is more challenging in ap2. So heavier flywheel was used to try and keep revs up between shifts, so you wouldn't drop out of vtec.

But the heavier flywheel ended up making shifting slower, offsetting much of the 'benefit'. A lighter flywheel, and a good driver, can shift faster than the increase in how fast the rpms drop, doing a better job of staying in vtec between shifts. But a 'lesser' driver might actually have a much more difficult time staying in vtec, if their shifting rate doesn't increase enough.