Exhaust butterfly valve

[Racer-X]

So I'm tempted to remove the cat and go with an aftermarket exhaust ... possibly even the 10R headers ... but there is something that perplexes me.

Yamaha came out with this nifty little thing called exup ... a butterfly valve in the exhaust to regulate exhaust back pressure. They originally did this to help reduce emissions but they soon found that it boosted low to mid range power and torque. My first Yammie was a pre-exup 87 FZR1000 ... more like a 750 with a screaming top end. Next one was an exup equipped 95 FZR1000 ... that one had grunt. The difference was notable.

I note they 10R headers don't have the valve and those of you that have used a mid pipe have removed the valve altogether. Doesn't this neuter the bike's low and mid range power? What am I missing?

[PhukDD]

I have not noticed any neutering but do not understand the physics behind it. In my mind with a restrictions of the cat somehow the valve does that and with the cat gone not needed. Or magic...either way runs like a raped ape.

[Champ87]

Doesn't this neuter the bike's low and mid range power? What am I missing?

Like you I was concerned about loss of mid-range with the exhaust valve removed. Concern vanished when vcyclenut posted up his dyno results. At every point through the rpm range his ZX10R setup produced more torque and, consequently, more power. Nothing you could describe as neutered.

BTW - I had an FZR1000 EXUP too. Great bike.

[Racer-X]

Yeah its tough to argue with a dyno ... thanks for the replies folks