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Old 15th September 2007, 20:30   #1
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Default Velocity stack. Does it really help in performance?

I've wanted to ask this question since a very long time.

Wikipedia says:
Quote:
Modified engines often have the original air box and associated ducting removed and velocity stacks are installed as aerodynamic replacements.


Although “racy” in appearance, velocity stacks do not usually have a major impact on airflow or performance. Most fuel systems already incorporate some kind of tapered entrance, nullifying what gains might be had from a velocity stack.


Beyond air flow improvement a velocity stack may be useful in containing "stand off" which may result from removing the original ducting. "Stand off" is fuel which is spit back out of the intake by pulsing action in the intake system. A velocity stack gives the engine a chance to re-inhale that fuel which can be helpful.

The old GP spec engines used to have these intake trumpets fitted to their carb or throttle bodies. Most of the old racing motorcycles also had these fitted on to the carb mouths. I have seen this either fitted inside the air box or it is fitted without airbox.

So my question is does this device actually help in increasing performance?
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Old 15th September 2007, 23:32   #2
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Originally Posted by Sankar View Post

The old GP spec engines used to have these intake trumpets fitted to their carb or throttle bodies. Most of the old racing motorcycles also had these fitted on to the carb mouths. I have seen this either fitted inside the air box or it is fitted without airbox.

So my question is does this device actually help in increasing performance?
I am unable to figure out the setup in the first picture. The second picture is however, more familiar. It is called the ITB (Individual Throttle Body) Setup. Simply put, each cylinder has one throttle body to itself. The engine in the pic is a V-8, hence the 8 throttle bodies. At least that is what it should be, if not it might be just a ornamental fixture.

I also doubt if the "swirl factor" alone would achieve noticeable performance gains i.e. if trumpets are used with stock TB/Carb setup.
Not clear about the first setup at all, though. Experts please oblige.
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Old 16th September 2007, 09:38   #3
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Imho the first pic is also has individual throttle bodies (on a flat 4 motor) but the stacks are placed inside the airbox which is to be sealed and fed by a turbo.

When i opened an Avenger's airbox i found a plastic velocity stack thingy sitting inside it. I just wanted to know if this is retrofitted on to an engine which doesn't have one would it be of any benefit.
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Old 16th September 2007, 10:46   #4
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Originally Posted by Sankar View Post
Imho the first pic is also has individual throttle bodies (on a flat 4 motor) but the stacks are placed inside the airbox which is to be sealed and fed by a turbo.

When i opened an Avenger's airbox i found a plastic velocity stack thingy sitting inside it. I just wanted to know if this is retrofitted on to an engine which doesn't have one would it be of any benefit.
Oops its a boxer 4. Forgot about that. I thought about it but when one thinks boxer engines nowadays, the only things that come to mind are the guys from Stuttgart- the Porsche flat-6 motors.

Yep that plastic/rubber thingy is also inside the Karizma airbox. It is a sort of S shaped double barreled tube under the seat which opens in the airbox. I had once removed it and the bike had cold start issues and when I took it to my mech, he said that the bike is running lean so put it back. I didn't take his explanation, but once I put it back; the bike went back to normal.

Hmmm.. This is an interesting thread, now even I am curious to know more about this stuff.

@tuners: Please shed some light on this and enlighten us.
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Old 16th September 2007, 12:50   #5
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supposed to be good for digestion, oops i meant better combustion along with harmonics. something to do with tuned length thingie if am not wrong.
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