velocity stacks in air box

[speedcostsmoney]

inside the velocity stack, yamaha created a high velocity port just before the carb venturi, meaning they made the velocity stack smaller by 19 % , for about 1.5 inch to accelerate the air speed to get better atomization at the needle and get more air into the pilot jet. did a test cut the velocity stack 3 inches from carbs added k&n pods went for ROAD TEST TOTALLY DIFFERENT BIKE than with just the k&n stage 7 of course by the way, better throttle reponse.guessing found 5 HORSEPOWER that was missing :th_image003:

 

[MaxMidnight]

If you are gaining power at one point then I suspect that you will be losing it somewhere else.

It is extremely rare that you get owt for nowt.

 

[wildweasel_pt]

Thats why the VMX17 uses a system that changes the stacks geometry (similar objective as a variable geometry turbo). It uses a broader range of RPMs.

 

[speedcostsmoney]

it gives a better air flow so the upside is better air fuel mix which is from 1000 rpm to 9000 rpm nothing wrong with that

 

[gamorg02]

i think maleko did some researach with stacks on the stg 7 filters a while back. i can't find the thread tho

 

[MaxMidnight]

it gives a better air flow so the upside is better air fuel mix which is from 1000 rpm to 9000 rpm nothing wrong with that

Not sure that I agree that it will improve air flow - what it will do is to charge natural harmonic point of the intake system, i.e. where a positive pressure wave will give a 'ram' effect to the incoming charge.

With an inlet tract length of 11.6" Yamaingha have tuned the intake to produce maximum torque around 7750 r.p.m.

By shaving 1.5" off the stacks you have moved this point up to around 8900 r.p.m.
This will be fine for W.O.T. but won't help drive-ability at low engine speeds.

The above, of course, is theory and the only sure fire way would be to do a back to back test on a dyno to establish the facts.

 

[maleko89]

Shorter velocity stacks are good for top end....longer low-midrange. It wasn't my research but it was found that 3 inch stacks offered best compromise. I have 3 inch stacks made from 2 inch diameter copper tubing.

 

[johnpclynch]

This is my current setup, 54mm Carb Trumpets from eBay
I find the response is much crisper and the sound through the K&N is 10x better :clapping:

 

[Diablotin]

Not risk of air leak where the stacks are sitting?

Looks like a good alternative to the rubber ones.

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[johnpclynch]

Not risk of air leak where the stacks are sitting?

Looks like a good alternative to the rubber ones.

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I used part of the old stacks and a bead of silicone under the airbox
It works now but it will make adjusting the carbs difficult, I'm thinking up ideas to improve it, maybe go in the direction Sharky went
http://vmaxforum.net/showthread.php?t=26957

 

[KJShover]

i think maleko did some researach with stacks on the stg 7 filters a while back. i can't find the thread tho

It was a great read.
It can be found here



.

 

[speedcostsmoney]

sorry guys but READ THE POST cuz no one seems to understand 3 inches from the bottom of the stack HELLO READ BEFORE YOU ANSWER AND AT LEAST give an answer that goes with the subject, better air/ fuel mixture better combustion at any rpm think about this before you answer

 

[srk468]

inside the velocity stack, yamaha created a high velocity port just before the carb venturi, meaning they made the velocity stack smaller by 19 % , for about 1.5 inch to accelerate the air speed to get better atomization at the needle and get more air into the pilot jet. did a test cut the velocity stack 3 inches from carbs added k&n pods went for ROAD TEST TOTALLY DIFFERENT BIKE than with just the k&n stage 7 of course by the way, better throttle reponse.guessing found 5 HORSEPOWER that was missing :th_image003:

You didn't do dyno or track testing before and after, just saying your guessing your making 5 extra horsepower doesn't make it so.. Not trying to be a dick bud just stating the facts. All of what the guys have been stating here is general carburetor theory and is all relevant but to claim a benefit and not offer proof of said gains will draw criticism.

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[88vmx12]

You didn't do dyno or track testing before and after, just saying your guessing your making 5 extra horsepower doesn't make it so.. Not trying to be a dick bud just stating the facts. All of what the guys have been stating here is general carburetor theory and is all relevant but to claim a benefit and not offer proof of said gains will draw criticism.

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The Swords have come out!

 

[srk468]

Sorry, not trying to make trouble I was just expressing a point...

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[speedcostsmoney]

no problem with critcism, just makes me laugh when people respond with a long winded response that does not fit with the subject at hand. no dyno test but better performance than just with the pods, improves the air velocity that you lose when removing the stock air box

 

[srk468]

no problem with critcism, just makes me laugh when people respond with a long winded response that does not fit with the subject at hand. no dyno test but better performance than just with the pods, improves the air velocity that you lose when removing the stock air box

Glad you understood my point bud.. Just for shits & giggles you should try the swap at the drag strip, it would be great to see the actual difference

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[CaptainKyle]

Glad you understood my point bud.. Just for shits & giggles you should try the swap at the drag strip, it would be great to see the actual difference

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Yep that is where I find out if my changes work . Its a true test

 

[redgambler]

Got any pictures? The stacks are inside the pods?

 

[speedcostsmoney]

http://img845.imageshack.us/img845/4518/img1293gv.jpg
http://img534.imageshack.us/img534/7678/img1294u.jpg
with this set up you keep the air velocity that yamaha calculated upgrade from 2 inch copper pipes