I bought the pro circuit slip on and it really made a big change in low end ,and also added the K&N filter and I was really pleased with the out come, those 2 small mods will give u a noticeable change in your low end.slip on only $180.00

 

I am looking into selling one of my 400EX's and catching one of those good deals on a new DS. Does WB make the R4 for the DS? I really like the looks and sound of it.

 

hylton400ex

As far as the R4 goes for the DS, I'm pretty sure they do make it. I'm skeptical of it though, in the DW test of various exhaust pipes on the 400EX, the R4 came in way behind the E-Series. I have the E-Series on my DS and it's got a great sound and very noticeable bottom end gain, a definite goodie.