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Discussion Starter #1
I've looked at every dyno chart I can find online and they all show a dip in torque from around 4500 to 6500. Of course, there is a corresponding dip in the HP curve.


Tuning A/F does not seem to do much.


Any ideas why???
 

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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.

https://www.hindle.com/Dyno_Charts/STREET/SUZUKI/2007_GSXR1000_Stock_VS_HindleFUllRACE.jpg


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:

http://www.kzrider.com/media/kunena/attachments/legacy/images/IMG_1133.JPG

We ask our motorcycle exhaust systems to do impossible things. Great performance from 1500-12,000 rpm, really?
 

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Discussion Starter #3
I hope you're right about the exhaust.


My M4 full exhaust should be on in a few days, and I plan to get a dyno untuned. Unfortunately, I won't be able to dyno stock for the comparison.


Depending on what it shows, I may (probably) will get a PC5 and get it tuned. Looks like the PC is needed for part throttle settings, even if full throttle looks good on A/F.
 

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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.
 

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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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