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Thread: 4 long stock velocity stacks in modded air box?

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    Senior Member sti491's Avatar
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    Default 4 long stock velocity stacks in modded air box?

    So I modded my air box, documented in my "de-snorkification" post. I bought a very cheap e-bay second air box to do this mod, because I was unsure I would like it. I like it. :-)

    I have searched on this subject here and elsewhere, and talked to Martin (aka Marthy) about theories on why Yamaha has two short stacks on the outside and two long stacks on the inside positions within the air box. A reasonable theory in general is long stacks help mid range and short stacks help top end, so Yamaha split them up to get the best of both worlds. I have a hard time buying into that, as having the outside cylinders intake properties being different than the inside ones just doesn't make a lot of sense to me unless someone can explain that reasoning better. Some have suggested it's due to the outside edge of the airbox top tapering down to accommodate the thank tilting down on top of it. Maybe. My theory is it has more to do with the OEM tall snorkel, that from car experience I believe was engineered more to reduce intake noise else than anything else, along with their estimates on just how much air the intake runners actual need.

    With the snorkel cut out, and having two boxes making it sort of easy to try different stack length combinations, I am thinking about trying all long stacks for better midrange. I have seen some posts including Martin's input that going all short gave a perceived better top end response. The only thing I found anywhere on going all long was on a 'Busa forum. They have the same short and long stack combo as us stock. There was actually a post with beforehand and after Dyno graphs going to all stock long stacks. There was a distinct midrange advantage.

    Has anyone tried this on our bikes? Any thoughts? I still have a timing advance mod and front sprocket change to try each separately before I try anything with the stacks, just curious what input I might get here.

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    Senior Member sti491's Avatar
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    Went with all short today. Bike runs strong. I figured with my other mods and the 15T front sprocket, I would favor top end over midrange. Whatever change it makes it's subtle, but glad I did it!

    Had my first power 2nd gear-smooth-as-silk wheelie never lifting off today leaned over the tank. Priceless!

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    What rpms are you running at 60-70 mph with that 15 tooth?

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    Senior Member sti491's Avatar
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    It is a very small difference from the stock 16T. Like the width of your tach needle. I don't even notice the difference.

    I am not sure exactly. I can look next time I ride later today. I think before it was maybe 6,000 RPM at 60 MPH? Add the width of the tach needle is close enough. Maybe 300RPM's? It is not objectionable to me at all.

    It will be interesting to see my mileage change. With my mods and Adv Gear Rev B map using 45/30/10 Acell pump setting, I was getting between 38.5 to 41 MPG depending on how hard I was riding.

    I highly recommend. Don't forget to lean forward in 1st & 2nd gear pulls though :-)

    Power wheelies are fun when you know they are coming, not so much when you don't!
    '12 Raven/DS70/PC/Block offs/Cut air box short v-stacks/Timing adv/-1 frt sprocket/Metzeler M7RR's/90o stems/spools/sliders/GD opener/Acc-USB plugs/Volt meter/Jewel switch/Phone mount/LEDs: Amber Jewel/Headlight/Smoke tail & flush frt & pod sig-DLR/underseat red sig-brake/DMP fender eliminator/Lithium battery/Puig touring screen/Grip Puppies/Seat 1.5" higher/Rox 1" up & back risers/Gear Indicator/KTM tail pack/M1 alarm/CC/Tank Pads/SS BL/3 back surgeries/Old fart balls of steel/Happy to be here.

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