 Jenks Velocity Stack... who knew?
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Joined: Feb 2005
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OP
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Well this one came as a surprise. A customer told me that the Jenks Velocity Stack for the std/T100/Thrux/Scrambler jsut might fit the America & Speedmaster. And it does indeed. At least it fits my 2002 America.  My customer thought that there might be some difference(s) in the shape of the filter access door between early models and newer ones. Can anyone confirm this? Thanks! /Mike BellaCorse.com
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Re: Jenks Velocity Stack... who knew?
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Joined: May 2007
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Worn Saddle
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Worn Saddle
Joined: May 2007
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All of the air filter clamps I have (04 America, 01 Bonnie, 04 Thrux) are interchangeable. They do have different moldings on the surface but the air filter clamp side appears to be identical...as far as I can tell the only dimensional difference is the length of the filter. That messy wire bundle cap should tuck in neatly (with a little coaxing) beside the stack just it does on my home made version: 
A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort. Herm Albright (1876 - 1944)
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Re: Jenks Velocity Stack... who knew?
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Joined: Jul 2006
Posts: 1,337
Learned Hand
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Learned Hand
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This isn't how a velocity stack is supposed to work. A velocity stack should be on the carb throat. It actually increases the velocity of airflow and improves the flow. Putting one in the intake of the air box does neither of these. The air still has to travel the filter and all the of the snorkles/ difussers. Yo umay gain some HP, but it would be from removing a restriction (the inlet). Looks cool, though. 
2002 Bandit 1200/ GSXR cams/ 1277 BB Kit/ Holeshot header and can/ 38mm flatslides/ a good head/lotsa hp/lotsa tq- lots of rear tires...
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Re: Jenks Velocity Stack... who knew?
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Joined: Sep 2007
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Aside from Cowtipper's note, it should help the overall breathing & smoothing the airflow into the filter area of the intake assembly. Not the best design for maximum power gains, but it will help aid in laminar flow. I know this for a fact as I did the same velocity stack on the outermost intake area of my Subaru WRX some years ago. Thanks again Mike! Jim PS - Anyone know if there are any differences in the intake inlet design between the 790cc & 865cc motors? Question of the day for me anyway...  PPS - Duh. Now in "redundant question mode." Mike seems to have already covered my bases on asking this question... Oh well, I'm off to bed now. 
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Re: Jenks Velocity Stack... who knew?
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Joined: Feb 2005
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Quote:
Putting one in the intake of the air box does neither of these. The air still has to travel the filter and all the of the snorkles/ difussers. Yo umay gain some HP, but it would be from removing a restriction (the inlet).
Not necessarily true. The idea is to speed-up the airflow as it makes it's way through the intake trac. That's why you see such devices on automobile mass air sensors, way up-stream of the throttle body. The velocity stack compresses the air charge, both speeding it up and cooling air temp. Merely pulling-off the snorkel is not going to give you equivilent performance as the velo stack. That's been well proven over at the 360° camp.
/Mike
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Re: Jenks Velocity Stack... who knew?
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Joined: Jul 2006
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Learned Hand
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Learned Hand
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Quote:
...Anyone know if there are any differences in the intake inlet design between the 790cc & 865cc motors?
They are the same airbox.
2002 Bandit 1200/ GSXR cams/ 1277 BB Kit/ Holeshot header and can/ 38mm flatslides/ a good head/lotsa hp/lotsa tq- lots of rear tires...
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Re: Jenks Velocity Stack... who knew?
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Joined: Jul 2006
Posts: 1,337
Learned Hand
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Learned Hand
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I want to say that I beleive the Jenks product is a fine product and a great alternative for those wanting to keep their airboxes "stock", but improve the power potential of their machines. However, I believe there is some confusion about what a velocity stack is and does. This thread is probably in the wrong place, too. That said; Quote:
Not necessarily true. The idea is to speed-up the airflow as it makes it's way through the intake track. That's why you see such devices on automobile mass air sensors, way up-stream of the throttle body. The velocity stack compresses the air charge, both speeding it up and cooling air temp. Merely pulling-off the snorkel is not going to give you equivilent performance as the velo stack. That's been well proven over at the 360° camp.
/Mike
I respectfully disagree. 
There are velocity stacks at MAS' on cars because a velocity stack is an efficient design.
Velocity stacks do not "compress" air. Compressing air would actually heat it up, and thats not desirable. What they do is increase air velocity and smooth air flow by improving on an inferior design. It is possible to tune for power in a specific range of the power band (i.e. midrange, top end) by adjusting the length of the tube, but the tuning would only effective on a very finely tuned and high performance machine. Our vacuum slide carbies would likely not react to such incremental tunings anyway- way to imprecise. But other than that, a velocity stack does not actually make power.
I guess the point I'm trying to get to that a velocity stack is nothing more than a very efficient intake design.
Adding a velocity stack vs. pulling the snorkel only improves on an inferior and restrictive intake design. Just as pulling the snorkel increases performance over stock, opening the the intake port and shaping it to be conducive to air flow (drag coefficient of 1 (a VS) vs .9 (a blunt tube)) will increase performance.
This can also be achieved with inverted velocity stacks within a high flow filter.
Hope this helps 
2002 Bandit 1200/ GSXR cams/ 1277 BB Kit/ Holeshot header and can/ 38mm flatslides/ a good head/lotsa hp/lotsa tq- lots of rear tires...
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Re: Jenks Velocity Stack... who knew?
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Joined: Jan 2005
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Learned Hand
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Learned Hand
Joined: Jan 2005
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Thanks Mike for bringing a new product to light. Maybe a dyno run on the same bike would be best. Surely better than physics 101. I have the freak on so it's not for me anyway. I could however lose about fifty pounds and probably gain more performance than any mod I could make to the bike.
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Re: Jenks Velocity Stack... who knew?
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Joined: Sep 2007
Posts: 568
Adjunct
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Joined: Sep 2007
Posts: 568 |
Quote:
Quote:
...Anyone know if there are any differences in the intake inlet design between the 790cc & 865cc motors?
They are the same airbox.
Thanks Cowtipper! And thank you for the insightful post on velocity stack works 101 as well. 
Ride safe,
Jim
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Jenks Velocity Stack... who knew?
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Joined: Mar 2007
Posts: 807
3/4 Throttle
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3/4 Throttle
Joined: Mar 2007
Posts: 807 |
Does anyone have a cutaway diagram or line drawing of the P-twin airboxes tehy can post up here?
Cheers, Neill
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Re: Jenks Velocity Stack... who knew?
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Joined: Jan 2005
Posts: 7,643
Monkey Butt
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Monkey Butt
Joined: Jan 2005
Posts: 7,643 |
Is this what you're after Neill 
Ray(UK)
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Re: Jenks Velocity Stack... who knew?
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Joined: May 2006
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Loquacious
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Loquacious
Joined: May 2006
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Hey Brian, do you know if those would fit on a Speedmaster?
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Re: Jenks Velocity Stack... who knew?
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Joined: Jan 2005
Posts: 5,172
Saddle Sore
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Saddle Sore
Joined: Jan 2005
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Well performance or not, at least it would keep the debris out of the filter after the snorkel is removed... The small animals too.
More flags
More fun!
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Re: Jenks Velocity Stack... who knew?
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Joined: Dec 2006
Posts: 7,028 Likes: 8
New Tires
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New Tires
Joined: Dec 2006
Posts: 7,028 Likes: 8 |
You're right, I know two different Bonnie riders who's bikes wouldn't run in the spring. Seems a family of mice were nesting in the air filter. They had both removed their snorkles.
I installed a Jenks velo-stack on my Thruxton, rejetted, installed uni filter and predator pipes. WOW! Now that it has been confirmed that they will install on my America I think its a GO.
Every normal man must be tempted, at times, to spit on his hands, hoist the black flag, and begin slitting throats.
H. L. Mencken
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Re: Jenks Velocity Stack... who knew?
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Joined: Jan 2006
Posts: 7,694 Likes: 22
Monkey Butt
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Monkey Butt
Joined: Jan 2006
Posts: 7,694 Likes: 22 |
The uni and pipes did it.
The length of the track from carb to intake valve is calculated along with the variable for the stack. The stack smooths the harmonic balance of the air to improve atomization. Its a happy medium, tuning for the sweet spot. On our bikes you would tune the stack(s) to probably 4500 that would give improved balance in a range up and down of about 1000 RPMs meaning from 3500 to 5500 you get better atomization. Most tune to midrange. At WOT its usually a gas thing that runs you out of power not atomization.
Anyhow, in my humble opinion, putting a stack in a box prior to the carb on the wrong side of the filter does absolutely nothing. Once the air leaves the stack and enters the box the balance is gone.
Your airbox functions like a velocity stack. The volume of air outside the filter has been calculated by the engineers to feed the right harmonic balance to the intake.
I try to aggravate one person a day. Today may be your day.
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Re: Jenks Velocity Stack... who knew?
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Joined: May 2007
Posts: 6,432 Likes: 1
Worn Saddle
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Worn Saddle
Joined: May 2007
Posts: 6,432 Likes: 1 |
Quote:
Anyhow, in my humble opinion, putting a stack in a box prior to the carb on the wrong side of the filter does absolutely nothing. Once the air leaves the stack and enters the box the balance is gone.
I can't argue that this isn't true, all I can say is that it made a significant difference in throttle response on my bike and it seemed to increase the engine's power.
A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort. Herm Albright (1876 - 1944)
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Re: Jenks Velocity Stack... who knew?
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Joined: Jan 2006
Posts: 7,694 Likes: 22
Monkey Butt
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Monkey Butt
Joined: Jan 2006
Posts: 7,694 Likes: 22 |
Oh, I believe you, just having trouble wrapping my brain around that one.
I try to aggravate one person a day. Today may be your day.
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