DYNOJET's website dyno charts show a 1.3HP gain on the 400EX by removing the airbox lid, installing a K&N filter and properly re-jetting

then WHITE BROTHERS website dyno charts show a little more than 0.5HP gain by installing their E-Series slip-on silencer, and that no re-jetting is re-quired.

If you spend almost $400 for both mods, you only get a total of a 2HP gain! does this sound technically correct? and if so, who in their right mind would do it?

 

Atleast they are honest. Some people just slap on 11 hp gain bull crap.

 

If you do the math thats 200 a horsepower. Not much of a return on the investment!!

 

Considering that you are starting off with probably 20 or less horsepower, that would be a 10% or so gain. You can only expect to get so much from a motor.

 

10% isnt that bad. More power is more money

 

That's PEAK horsepower gain, which by far doesn't tell the whole story. Go grab the latest Dirt Wheels (with the 400ex exhaust shootout), and you'll see what a K&N, silencer, and no airbox lid will do on a 400ex. The greatest peak HP gain was a whopping 1hp, but there was a gain of 4-5hp in the midrange (4000-6000rpm), which is a HUGE gain!! That means gobs more midrange torque, with a little more peak HP to boot.

 

The dyno sheet that came with my R4 claimed a little under 2hp gain. With a 155 main and K&N, 400's that I use to out drag were now beating me by the same margin. I was very disappointed.

My advise is buy the full system for it will perform better than stock now, and even better with future mods. Now I have to go out and spend an additional $470 (R4=$209) or so for a full DMC to accomodate the 440. How much do used R4's go for anyway?