The last time I checked they were rated around 96-98. Once the packing starts to wear out it goes up of course. And by taking out the silencer/spark arrestor it goes up much much more. I can only run my Z400 with the yoshi full system without the silencer/spark arrestor at Pismo because it's way to loud to run at Hollister like that.

 

in www.ctracing .com ther is a dirt wheels shootout for the z400 under z400 that shows every big brand and dyno charts

 

ridefreak: yosh has 3 different spark arrestors or end caps u can choose from, the one that comes standard is rated 96-98db, the low insert u can buy is around 93db, and no insert is around 101-103db (very loud). if u ride on public land is suggest using an insert, loud isnt always best, the standard insert is fine tho. if u go with yosh, i suggest gopartsdirect. heres a link: http://www.gopartsdirect.com/atv/ite...&Placeholder=0

 

That must be a very generous dyno. It's the first one I've seen giving a stock Z more than 28-30 hp, or getting more than mid 30's with just pipe/airbox mods.

The Yoshi full comp comes with a spark arrester "tec" insert that is supposed to keep it between 93-96 db. I don't know about the others, but mine gives a very noticeable kick over stock throughout low-mid-top with the insert installed and sounds cool but not obnoxious. I'm very happy with it.