A 16 tooth front sproket on a stock 400 ???? are you insane ...what a toilet...I run a 450 ex fully modded and a 16 tooth up front ...it works perfect but there is no way I would run that combo in a stock 400 ..I would lay money that it would never pull high gear to the limmiter...

 

Biggy...you are on the right track.

I had a mild (416cc + pipe + free-flow filter + proper jetting) 400ex and when I switched to a 16 tooth front sprocket, acceleration was lost.
This was done by a "real world" test. When I lined up against my bro's stock 2000 'Shee with the stock gearing, I could pull the 'Shee till I shifted to 4th, then, like clockwork, I look to my side and see the 'Shee go ripping by (on pavement by the way).
With the 16 tooth front sprocket bolted on, we would pull out and the Banshee would immediately start pulling away. Don't really know if any speed was gained on top end because the race was already over.