# Velocity Stack mod: Annular Holes (Discuss)



## thebigmacd (Aug 17, 2004)

Just throwing an idea out there, since I can't find any discussion on the topic on the net.
My idea is to drill several holes symmetrically in a ring around the velocity stack at/near its smallest point, using Bernoulli's Principle to draw additional air into the venturi at high flows. Location and hole size/count would obviously have to be optimized based on rpm (wave tuning) and venturi size (velocity tuning), respectively.
My brother-in-law is highly skeptical because race teams don't use it on their engines. I'm less skeptical because (a) I can't find any evidence that anyone has even tried it in the first place, and (b) that's how carbs draw fuel into the airstream.
The principle is used quite a bit outside of the automotive engine world, in airbrushes/paintguns/sandblasters, and science labs as vacuum pumps.
See here for a demo
http://hyperphysics.phy-astr.g....html
http://hyperphysics.phy-astr.g...ml#c1


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## Svedka (Jul 4, 2008)

*Re: Velocity Stack mod: Annular Holes (thebigmacd)*

do it and report back


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## B4S (Apr 16, 2003)

*Re: Velocity Stack mod: Annular Holes (Svedka)*

Well, provided the flow through the ITBs isn't maxed out already, maybe it would work. Ultimately though, you're limited by the restriction of the throttle body itself.


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## thebigmacd (Aug 17, 2004)

*Re: Velocity Stack mod: Annular Holes (B4S)*


_Quote, originally posted by *B4S* »_Well, provided the flow through the ITBs isn't maxed out already, maybe it would work. Ultimately though, you're limited by the restriction of the throttle body itself. 

My application would be applied to F1-style turbocharged intakes where they have a single throttle and unrestricted stacks poking into the manifold.


_Modified by thebigmacd at 5:16 PM 1-13-2009_


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## B4S (Apr 16, 2003)

*FV-QR*

You mean like this? Throttle body pre-turbo?


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## ps2375 (Aug 13, 2003)

*Re: Velocity Stack mod: Annular Holes (thebigmacd)*

It's been in use for a long time to pump bilges on ships. I even had one that came with a waterbed to fill and drain it. The problem would be to get the correct amount of fuel, cause basically you're dealing with a large vacuum leak. You have no way of measuring the air taken in by the motor and run a rather large risk of going extremely lean and burning it up, even with an O2 sensor to check exhaust, can it react fast enough to keep it safe?
And it has been used in the racing world, NASCAR teams have tried to get away with this type of method on their restrictor plate motors in the past, to get more air than the plate will allow, of coarse, it is a rules violation and they are penalized for it.


_Modified by ps2375 at 7:19 AM 1-14-2009_


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## K2e2vin (Jan 9, 2009)

I've actually thought about doing the same thing.
For Hondas, there are two aftermarket companies I know of that utilize that technique. I first heard about it from Jeff at Import Builders. They were secretive about it and only said that it netted at least, IIRC, 8whp more than the other intakes(they utilized a velocity stack instead of a air filter though). I believe Weapon-R copied the design; it's called the "Secret" intake but they have diagrams and cuataways of their design.


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## xr4tic (Dec 10, 2001)

the stock rubber velocity stacks that came with my GSXR ITBs had slits in them. They are not at the lowest point, but close, they are moved up a tad so that they could be in the airbox.


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## stark22 (Feb 22, 2002)

*Re: (xr4tic)*

Fist what are attempting to do? Are you trying to increase power at redline? What is your redline rpm? Do you have solid lifter heads? Are you running on race fuel or street fuel? Do you have a dyno plot of your current engine? Are you running cycle throttle bodies, if so what liter size? Have you tried different liter size throttle bodies and re-run your ride on the dyno to see an impact on your torque curve? With all this said, do you believe your engine is loosing power at high rpm because the flow is being restricted at some point in your inlet system?
You first need to determine what is restricting your mass flow. 
If the venturi is restricting the flow, then yes, there is a potential to increase the mass flow by perferating the annulus which is increasing the effective area. If this is the case and the venture throat is the restrictor, why not run a larger venturi diameter and corresponding throttle body. If flow is being choked by some other down stream area, purhaps your intake valve, then your mass flow is set by this inlet area. To increase flow you would need to increase your inlet port size.
This is just my thoughts.
Ill add more later when I get out of work http://****************.com/smile/emthup.gif 



_Modified by stark22 at 4:57 PM 1-16-2009_


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## thebigmacd (Aug 17, 2004)

*Re: (stark22)*


_Quote, originally posted by *stark22* »_Fist what are attempting to do? Are you trying to increase power at redline? What is your redline rpm? Do you have solid lifter heads? Are you running on race fuel or street fuel? Do you have a dyno plot of your current engine? Are you running cycle throttle bodies, if so what liter size? Have you tried different liter size throttle bodies and re-run your ride on the dyno to see an impact on your torque curve? With all this said, do you believe your engine is loosing power at high rpm because the flow is being restricted at some point in your inlet system?
You first need to determine what is restricting your mass flow. 
If the venturi is restricting the flow, then yes, there is a potential to increase the mass flow by perferating the annulus which is increasing the effective area. If this is the case and the venture throat is the restrictor, why not run a larger venturi diameter and corresponding throttle body. If flow is being choked by some other down stream area, purhaps your intake valve, then your mass flow is set by this inlet area. To increase flow you would need to increase your inlet port size.
This is just my thoughts.
Ill add more later when I get out of work http://****************.com/smile/emthup.gif 

_Modified by stark22 at 4:57 PM 1-16-2009_

This is not for a specific car, it's just a general idea.


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## thebigmacd (Aug 17, 2004)

*Re: FV-QR (B4S)*


_Quote, originally posted by *B4S* »_You mean like this? Throttle body pre-turbo?

No, but that is cool. Eliminates the need for a BOV.
I just meant a manifold with a single throttle plate and velocity stacks poking into the manifold.


_Modified by thebigmacd at 2:02 PM 1-16-2009_


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## thebigmacd (Aug 17, 2004)

*Re: (xr4tic)*


_Quote, originally posted by *xr4tic* »_the stock rubber velocity stacks that came with my GSXR ITBs had slits in them. They are not at the lowest point, but close, they are moved up a tad so that they could be in the airbox.


Thank you good sir! I was told on another forum by an engineer and others that it would screw everything up but Suzuki evidently didn't think so!
These ones go even farther with the idea:










_Modified by thebigmacd at 2:16 PM 1-16-2009_


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## K2e2vin (Jan 9, 2009)

Don't listen to engineers(in general...as there are some who know what they're talking about). My friend had two engineers tell him a turbo off a DSM would not work in his Honda, and labeled him a "tinkerer that just thinks up ideas that fail". There are websites dedicated to homemade turbo setups on Hondas.
Also, where I use to work(BCP Caterpillar), they had engineers tell management that various things should work because the computer said it should; any problems were blamed on the technicians. It isn't until after a couple of months later when they finally accept the technician's idea on how to fix it or how it should be designed.(Engineer vs. Engineering technician...not many realize there's a difference).
The GSXR slits are not for the same purpose that you're looking to do. IIRC, they were for reducing intake pulses to help mid-range power.
The picture about is exactly what you're looking for. Looks like they intentionally try to take advance of the bernoulli effect. I've seen something similar on a bike carburetor but it was just to reduce turbulence and direct air that was entering from the side.


_Modified by K2e2vin at 11:23 AM 1-16-2009_


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## thebigmacd (Aug 17, 2004)

*Re: (K2e2vin)*


_Quote, originally posted by *K2e2vin* »_Don't listen to engineers(in general...as there are some who know what they're talking about). My friend had two engineers tell him a turbo off a DSM would not work in his Honda, and labeled him a "tinkerer that just thinks up ideas that fail". There are websites dedicated to homemade turbo setups on Hondas.
Also, where I use to work(BCP Caterpillar), they had engineers tell management that various things should work because the computer said it should; any problems were blamed on the technicians. It isn't until after a couple of months later when they finally accept the technician's idea on how to fix it or how it should be designed.(Engineer vs. Engineering technician...not many realize there's a difference).
The GSXR slits are not for the same purpose that you're looking to do. IIRC, they were for reducing intake pulses to help mid-range power.
The picture about is exactly what you're looking for. Looks like they intentionally try to take advance of the bernoulli effect. I've seen something similar on a bike carburetor but it was just to reduce turbulence and direct air that was entering from the side.

_Modified by K2e2vin at 11:23 AM 1-16-2009_

Oh I know all about that...I'm a Control Engineering (Systems) Technologist in the construction industry; I'm usually banging my head on the wall over what the Engineering Consultants have come up with. I have met a few practical Engineers on site though, and unsurprisingly their jobs always turn out more profitable for everyone.
I am willing to admit that the stack idea may not have much gain. It's funny though how when someone comes up with an idea that is not widely known or understood, the group of people who are supposed to be the innovators of the world get their backs up against the wall and say that because not everyone is using it now (or they haven't heard of it before), it must be *fail*.


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## B4S (Apr 16, 2003)

*FV-QR*

To be honest, you've got my curiosity piqued. I have a spare set of horns for my carbs, maybe I'll drill a few holes and try a before-and-after dyno test this spring, since I have planned a couple of trips to the dyno anyway.


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## stark22 (Feb 22, 2002)

*Re: (K2e2vin)*


_Quote, originally posted by *K2e2vin* »_Don't listen to engineers

_Modified by K2e2vin at 11:23 AM 1-16-2009_

Ha.


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## Svedka (Jul 4, 2008)

*Re: (thebigmacd)*


_Quote, originally posted by *thebigmacd* »_
Thank you good sir! I was told on another forum by an engineer and others that it would screw everything up but Suzuki evidently didn't think so!
These ones go even farther with the idea:









_Modified by thebigmacd at 2:16 PM 1-16-2009_


oOo

Where do i get a set of these to try out?


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