I wish there was a one sentence answer, or even a "this is what it is".
It might be a bunch of different things. Sometimes a/f ratio, it can be exhaust, timing, or it can be a designed combination of all things put together. Likely , on purpose as it probably corresponds to some test point in emissions sound testing.
On this specific bike, my guess would be exhaust. Look at this dyno chart for the 07 gsxr 1000. Its an 07, but look how the midraneg dip was eliminated.
By the way, you have seen "midrange dip" unless you tried one for the 1970-1980 era bikes with a real 4-1 exhaust. Now, we use 4-2-1 and it very much minimizes this dip, but probably costs some hp up top. Heres one you wont forget:
For me, upper end numbers were great fun....right after you install the exhaust, you take it to redline. Then, you do it again. And thats about it. Common cents kicks in, and you realize you like your freedom and a lack of jailhouse sodomy is a good thing.
At this point, and forever after, part throttle performance is everything. Having your bike tuned to where is awesome at part throttle openings is a far bigger thing, to me.
Any chance the exhaust valve affects this or do we see the same with the arrow headers as well? If it goes away with a full exhaust then I'll play with the exhaust valve when it goes on the dyno. I'd love to fit a full exhaust but I also don't want to wear the fines I'd face for defeating emissions equipment.
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