power question

[cbizzle82]

ok i have a 2005 400 ex with a white bros e2 slip on and jetted everything else is stock now my question is why are me and my boy with a bone stock 06 400 dead even when we race im mean dead even even if we switch riders for the weight difference i mean the quads are dead even i was wondering if the stock air box and filter was hurting me but i would still expect some gains any help will do thank u

[wilkin250r]

Despite what the advertisers say, a pipe really doesn't give you a whole lot of gain, especially on a 400EX. The fact that you and your buddy are dead-even really doesn't surprise me.

In theory, you should see a horsepower or two, but you might lose that if your jetting isn't spot-on. Heck, you'll see 1 or 2hp variation just from one 400EX to another, even bone stock, just because that's the way the world works.

[cbizzle82]

yea i guess everyone expects miricles with a pipe and jet lol.
also would i have to re jet if i change the lid and air filter

[Rip_Tear]

Originally posted by cbizzle82
yea i guess everyone expects miricles with a pipe and jet lol.
also would i have to re jet if i change the lid and air filter

Most likely, and that would help with the pipe.

[wilkin250r]

Yes, more so than a you would with a pipe.

When the piston travels downward and the intake valve opens, it creates a vacuum to pull air in, and drops the pressure in the intake tube. At that point, the carb bowl is at a HIGHER pressure than the intake, and that's what forces fuel to travel upwards (against gravity) and into your intake.

In reality, it's a combination of this pressure difference and the venturi effect, but let's just stick with one concept for now.

Removing the air box and using a high-flow filter, air is pulled in much easier. Therefore, there is less pressure difference between your intake and your float bowl. Less pressure difference means less fuel. Therefore, you need to increase your jet size to get back to the proper mixture.