Just curious if anyone has run both airboxes and can comment on any performance gains. I see the older klx250 & the klx 300 both run the larger boot.
thx
marc

 

What's the difference? I can't imagine there being any performance difference unless the opening/intake hole is bigger. I didn't realize there was really any significant difference in the boot and airbox. If they have different part numbers, I doubt it has anything to do with more air or performance.

 

I'm seeing that the boot flairs just before the carb, the waffle reinforced area appears larger than the straight hose of the newer 250. I'm just wondering if that might help it breath better at mid to topend.
marc

 

marc, I can almost guarantee without question that the change would have nothing to do with a performance gain. If anything, Kawasaki determined a change was needed because of material/shape design for a wear issue, interference with a change in some small component requirement (like a shock collar or spring), or who-knows-what. That's a good catch on noticing the change, but I'm sure it's not performance related.

 

The KLX250/300R airboxes and boots are very different from the KLX250S version. The 'R' version is like what you traditionally see on a dirtbike: a simple plastic box with a large rubber boot that forms the front of the airbox, wraps around the shock and connects to the carb. The 'S' version is a multi-piece plastic box with a very short section of rubber tube between the box and carb; the front of the box is plastic and includes the offset to get around the shock.

Not sure the reasoning why Kawi changed it, but my guess is EPA emissions or noise compliance. The 'R' box sure does look better from a fluid dynamics perspective. I bet the 'R' box does have more power potential...though maybe only very slight. I will say that carb maintenance would be easier with the extra flexibility inherent in the 'R' type boot.

 

Lutz, I think the two systems are way more similar than not. Even the airbox lid is the same part number between the two. I think I discovered why the airboot from the box to the carb is different when I was modding my rear suspension. The shocks between the 300 and '06/'07 models are very similar but not exact. Also the 300 uses a longer spring despite these models having the same exact travel. Especially the taller spring required a slightly different airboot. I used the 300 spring from Eibach on my '06, and I had tweak a couple of minor things to keep it from rubbing on the airboot. I don't think there's a nickel's worth of flow difference between the two designs, and that's the only way you'd get more performance. The biggest restriction is the opening in the top of the airbox which is easily remedied. If there was any noticeable lack of flow elsewhere in the two systems, I think we would have seen it become evident with the use of the 351 kits and the TM36 pumper carb.