What Big Bore Will Do For You
These runs are on an 05 YFZ, bone stock at 439cc vs well-modded at 439CC vs a +3mm 470cc Big Bore kit added.
Many, many times in the past I have had questions regarding the power value of BIG BORE kits. And it is always a less than effective/accurate evaluation to just tell someone 2~3 more peak HP and 2~3 more peak torque. The throttle response and added pull is from idle to the rev limit, and more power no matter what rpm you are at, hard to put into an explanation what adding power across the entire band really feels like. So here's a graphic representation of what it looks like on a dyno -- no changes other than going from 439cc 95mm bore to 470cc (468, really) at 98mm bore. Both setups are at 12.25:1 pump gas compression.
First graph shows that the power with the 470 is greater from idle to rev limiter, and that the power is just starting to "roll over" near the rev limiter. The stock bore is still on its way up at the rev limiter before, and the big bore setup had hit its peak a few hundred rpm before. The gains were at their greatest in the 7000 to 9000 RPM band, which is a VERY nice place to have the best boost occurring.
Before, the stock bore broke the 50 HP mark at 8200 rpm, and now the BIG BORE breaks it at about 7400 rpm. Just putting a piece of paper across the horizontal axis is an interesting study in how much sooner the power hits a certain rpm. If you look at the 56 HP mark, the big bore hits it about 1200 rpm sooner, and in riding, it feels every bit as dramatic as it looks.
Black = stock machine
Blue = modded stock bore
Red = modded BIG BORE
We've finally hit the "30 more hp than stock at the rev limiter point". :)
