KneeDragger - I havn't seen any specs on the increase changing the entire exhaust system will give but I'd guess it'd be pretty good. From what I've heard, the only one even being mentioned so far is Yoshi (stainless or titanium/carbon) with a price ranging from $500-$800. My sponsor mentioned he could get me the setup but there isn't an official part number yet.

I have the full yoshi exhaust on my Z400 now. It came with a spark arrestor/silencer and when I remove it I do get more power out of the motor since it 'breaths' better. Don't get me wrong, I did get more power with the yoshi system with the arrestor/silencer then with the stock pipe. The stock pipe looks pretty close to the oval Team Suziuki / Yoshi pipe I have on my Z400. Removing the attestor/silencer was pretty easy actually. Only takes about 2 min. Trust me, it makes a world of difference.

When I run my Z400 pipe 'open' it make a big difference. I only run the quad 'open' when racing or at Pismo/mojave due to rules at the local SRVA park. The suggestion that calzookie and I gave before was a cheap way to add more power before more parts become avaliable on the market. Since the cherrybomb was the only mode available thus far at my local dealer I bought it day one.... Still waiting on my darn nerf bars....

 

I think any aftermarker exhaust will make a big improvement. I would even consider taking the peeshooter out of the aftermarket exhaust if you won't be riding in an area that has a high fire risk (forest/brush). With the new EFI, the computer continually adjusts to air intake and exhaust rate. The quicker you can get the air in and out will improve the performance of your quad. Even if you don't run race fuel, I would still get the cherry bomb. I have read it still offers a performance gain on 91 octane. I am running 50/50 U4/91 gas. Don't just get the slip-on exhaust, pay the extra $150 for the header too.