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Discussion Starter · #1 ·
i was just wonderin, if shorter intake runner lenght gives you more hp up top, then why do people use velocity stacks?? or am i wrong in the theory that shorter intake length gives you more up top??
d-mann
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Length, diameter, shape, and probably a bunch of other stuff that I don't know about/images/icons/wink.gif all conspire with the rest of the engine (carbs, cams, valves, bore-n-stroke, combustion chamber, exhaust...) to determine the power curve produced.

So the definite answer to your question is: "it depends" /images/icons/laugh.gif

 

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well, you are correct that a shorter intake port helps produce higher peak power numbers at the expense of some mid and lower rpm power.

Velocity stacks come in different heights, and thus serve two purposes. A. Smooth the flow of air into the intake tract, B. Manipulate the power curve.

Check any Busa or newer 6R and you will see that there are two short stacks and two longer stacks. I know of a GSXR1000 owner, and some Busa owners that went to all shorties to try to increase peak power.

I don't know how much power we're talking about here, it's probably only 2-5 at best, but every little bit adds up!

BA
"<font color=blue>How about never, is never good for you??</font color=blue>"
 

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Discussion Starter · #4 ·
i realize that 1 and 4 have different heights on some bikes, but mine doesnt. theyre all the same height. i was gonna put on the stacks from a 92 model on 1 and 4 cyl since they are shorter. and see if i got any difference. just toyin around, but who knows, maybe it will work.
d-mann
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I don't know it the gains will be the same with the Kawi's but with my 1k Gix it made a bit more throughout the whole power range. Hopefully you'll have the same gains. I would have to say it made or it feels like it gained 3 to 4 throughout the power range, and I say that because it feels like it almost equals the gains of my Yoshi half system pipe. Attack makes some awesome stacks out of aluminum but they cost big time, around $250.00. A friend bought a set for his 1K and they are a work of art. Can’t wait to dino mine in July.
U.F.
 

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I have tried short stacks on both the 6r and the 9r.
For the 6r we ordered 1/4 stacks and cut the mounting tab off and they bolted on. They worked great with a 2hp gain. We rejetted the bike taking out the staggered jetting and got 1 more. So 3hp for a bolt on with no loss of midrange. Great stuff! This was all done with a standard Akro exhaust.

The 9r was a challenge. I bought an extra set of stacks and had a friend machine 10mm out of them and then we reglued them together. He machined them as a slip fit so they look like they came from the factory, very nice. I also tried some 98/99 intake manifolds since they are 12 mm shorter than the 00/01 manifolds. We dyno'd it all at the same day and..... the short manifolds with the short stacks don't work. We lost 3/4 everywhere. Just the short stacks worked good. We gained 2 on top and really didn't lose any down low. The funny thing was that it cleaned up the fuel curve really well. This test was done with a M4 pipe and a modified motor. (150 hp, stock pistons,cams,carbs)
Our shop is going to do some more work on the stacks and we may sell them.
 
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