Power comparison between 2 '99 YZ400's

[Pothole]

My friend and I both have '99 YZ400's. Both bikes are in about the same condition. His bike is all stock except for a White brothers E-series pipe on it, just the end section, not the header. My bike is all stock except for a Promoto end cap (with the spark arrestor screen installed) and a WR flywheel and stator. When comparing the two bikes power characteristics, his bike is alot snappier off the bottom, and feels like it has more power. Could that WB pipe be giving him that power advantage? As a side note, that WR flywheel is about 10-12 ounces heavier than stock, although I didn't notice really any power loss after installation, just a smoother powerband.

[Dano426]

The E-seris will give you a little more pep and power than the stock exhaust, but I think what you are noticing is your flywheel. The whole point of a heavier flywheel is to add mass to your engine so it will take longer to rev - hence be less snappy and have less tire spin.

[motocrosschump]

Ditto on flywheel

[onekyoung]

Definately the flywheel diff. Before and after FW installs are hard to notice a huge difference until you race a stock YZ, then the difference becomes painfully appearent ?

[Fastest1]

Not only does it take longer to accelerate, it takes longer to decelerate. Mass keeos the engine running in low speed situations.