Cormace, I am investigating a possible issue with the RS-2 and need your help. I am investigating whether or not the RS-2 is compatible with performance KLX250 headers or if it is a mismatch.

It concerns the size of the nipple on the RS-2 midpipe.

That nipple size is the key. Does it slip into the powerbombs' bell, and seal by only adding a smattering of high temp silicone - without the need of an exhaust gasket of any kind ?

If a gasket, of some sort, is required, then the O.D. of the nipple must be quit a bit smaller than the powerbombs' bell. If this is the case, then the RS-2 joins the DG's, and Delkevic's as being incompatible with performance headers.

Any and all midpipe-to-header connection(s) must be seamless and smooth to the gas flow.. Any nipple I.D. that does not match the header piping I.D.when it is shoved all the way into the headers' bell, creates an obstruction that completely destroys any performance potential - I found this out the hard way, on the dyno..

 

Klxster, I don't know if this will help you or not but the rs-2 comes with a factory Kawasaki gasket to go from the factory header to it's midpipe. It is the same gasket that comes factory on the bike. They just supply you a new one.

 

Ok, that is not a good sign..
Final determination may be easy for you - is the Yoshi nipple the same size as the stocker's - OD and ID ?

 

I'm not sure what you mean by nipple. If you mean, the area at the front most end of the Yosh pipe then yes I believe it is the same OD as stock as it fits inside the header with the deformable gasket Palmer812 mentioned. Also, the Yosh pipe works with the stock Kawasaki header (obviously) as well as the FMF Powerbomb as that is what I'm running.

I'd do the measurements to get you a more accurate answer, but my pipe is covered in exhaust wrap

 

This issue is quite simple - but very hard to explain in writing.. A FMF/HMF/TBR slipon fits both the stock header AND the larger FMF/Big Gun headers - and does both perfectly. Their midpipe nipple is so large that the stock header must have its' gasket removed completely before the FMF midpipe will slide into it..

The nipple is the end of the midpipe that slides into the header's Bell. The proper relationship is that the I.D. of the nipple is the exact same size(or larger) as the I.D. of the header piping (not the headers' larger bell slip joint).

If the RS-2 has a midpipe nipple that is identical in dimensions to the stock midpipe nipple, we have a really big problem - the RS-2 is not compatible with performance headers. And I will have to properly add the RS-2 to the Exhaust fitment thread..https://www.kawasakiforums.com/forum...rations-44444/

And you guys with performance headers will need to reinstall your stock header or replace the RS-2 with a compatible slipon.. The mismatch makes less HP and TRQ than the stock header..

 

Hmmm. I'm still not sure I get it. You're saying that the stock header is somehow less restrictive than the FMF Powerbomb even though the fitment of the Yosh midpipe into the Powerbomb header is the same as the fitment of the Yosh midpipe into the stock header? Sorry if I'm a little slow. Here is a pic of the FMF Q4 (before I returned it) next to the Yosh connected to the Powerbomb header. does that help answer our question?

 

Unfortunately, your pic does not answer the question - as to whether or not the Yoshi is compatible with the FMF headers..

I have circled the nipple of the Q4 - the Yoshi nipple is not pictured, but it will need to have the same exact dimensions of the Q4 nipple before it should be used with a FMF header.

 

The Q4 almost doesn't even need a clamp. It is a tight fit into the PB slip-joint (bell). All you need is just a thin smear of sealant on the nipple that is allowed to cure before running the engine. If the Yoshi is compatible, it will fit just as tightly and only need a thin smear of sealant in order to seal into the PB as well..????

 

Ah. I understand now. I'm pretty sure the nipple on the front of the Yosh midpipe is smaller than the Q4, Bummer.

 

Well we are gonna need something definitive on this - a proper picture or measurements. I figured that you installed both onto the PowerBomb and would know if the yoshi was a loose fit compared to the Q4..

If the Yoshi has the same size nipple as the stock silencer, you are killing your power levels everywhere via the bottleneck at the slip joint - the stock header will make more power than you have now..