I was doing some research on this... it's called the "white bunny" mod, it upgrades the stock 225mm clutch setup to a 240mm setup for more surface area and clutch options.
Info duplicated from http://forums.nicoclub.com/zerothread/227129
(taken from 240sxforums 240sxAddict/creator from another forum)
The "White Bunny Special" was first created and explained by s14turbose, the "white bunny" being his 98 S14 turbo SE. KA24's come stock with a 225mm clutch surface area, but using parts from other nissans allows you to run a 240mm clutch, which by logic gives you more tractable area for the clutch to grab onto thus reducing the chance of slippage.
We used the flywheel of a 1993 D21 Pickup(4 cylinder model), which is the standard flywheel to use because it carries the same crank bolt pattern as our cranks but is a 240mm flywheel. I believe any year will work, 87 being a common year people use but to play it safe use the 93 because I just installed one and it fit fine. There is also talk of lightened 240mm flywheels, but I have yet to see any that arent custom made.
Now the pressure plate and clutch disc are varied. We used the stock setup of the afor-mentioned 93 D21, but common clutches used are off the 280Z Turbo, the 300ZX Turbo, and the RB series clutches. You can use both aftermarket and stock as long as it is 240mm. But one rumor surrounding this special is the truck and 280Z clutch can hold balls of torque, some saying near 400ft/lbs and they still retain stock pedal feel and longer life than aftermarket clutches. I'm still searching for the answer, but I read it went on Mike Lee's T66 KAT, and it had no problems holding 500rwhp.
One very important point is that the 240mm clutch uses 9bolts to hold the pressure plate onto the flwheel, while your stock uses 6. Be sure to pick some up before you attempt this. Also, you'll have to break the small pin on the crank off to bolt up the flywheel, as it has no slot for it.
and of course here are the comparision pictures:
this is both setups(225mm and 240mm) set beside each other
example of size difference
White bunny test video
after about 2 cans of brake cleaner still had 2more to go
as a result of not running my dust cover this happen. i thought it would help with cooling, but was I wrong..................yup
more size difference pics
tools used to remove old worn pilot bearing for act bearing
putting new setup on
the little bulge that you see at the bottom of the dust cover is what the flywheel will grind down. when the noise has stopped, you will be able to insert your bolts at the bottom of the bell housing. after that, more noise will sound for about 1 minute. after that your all go.
My pictures ( total price $215 dollars)
I'm considering this down the line. For most of us stock NA KA guys, it's probably not necessary, but if you're going to be boosting and putting down the powah, it would be better.