This could be a MASSIVE topic.... But I can only light the fire before I get pulled into my work day.... Where to start?? On 450 class machines... The rule of the day when modding a monster is: "you are going to need more flywheel or you are going to waste a lot of power" Whether it's in uncontrolled wheelspin , or in too much power to make your riding rythm work.... You can build a monster that you CAN'T ride... Flywheel it up and all that power becomes controllable and useful... There are plenty of stock machines that are known for having too small an amount of flywheel mass right from the factory... Prone to stalling and lighting up tires with abrupt hit... Also... Thumpers, by virtue of single cylinders , wreak havock on valve trains and timing chains... With all their intermittent snap and slack between power pulses... You watch one strobe light study of a thumper timing chain and you will wonder why they don't just all snap on the first ride... I have experienced many crazy built 2 strokes that have personalities that order on pathologic ...lol... More flywheel makes the power and traction and a whole lot of things work... I am , of course , talking about the control of very strongly built engines with a wretched excess of power.... Not putting a big fly on something that is nutless to begin with.... Quick bit about what makes sand drag quads run at the top of the heap.... I have been involved in quite a bit of sand drag quad building... Even though I'm not a fan of drag racing myself I have done a lot of head work etc for the drag race crowd.... They spend a lot of money on VERY heavy tungsten weighted cranks and heavy flywheels.... The biggest step in our gearbox is the step from 1st to 2nd...biggest numeric hike.... They gear as TALL as you possibly can to still launch HARD in first gear... And shift ONLY ONCE during the race.. taking all that inertia and banging it at high rpm into the big jump to second gear... Unreal what one of those setups pulls like with a killer engine.... Unreal... Sooooooo... After all that... Time to talk about something I have not experienced... Too much flywheel mass initially...and making everything better by reducing flywheel weight... Adnohguy has mentioned big benefit, and no trials tractability loss, by dropping a lot of flywheel mass on our 230s... Who has done it? How much can be dropped? Who does the work? What's it cost? What are the results?