Turbo bellmouths/velocity stacks
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0.0 BAR
Joined: Oct 2005
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Turbo bellmouths/velocity stacks
I've been looking into them a bit, curious if anyone else has experience with them or knowledge of them. Here's the best info I've found so far. I plan on using one on the turbo for my next build 
They do look gangstur either way
"Seems like ASEC is getting some good old technical question here lately (IMG:style_emoticons/default/icon_wink.gif)
Ryan, velocity stacks change the airflow as exactly stated. They increase the overall velocity of the moving air going through the body. The wikpedia page shows in basic terms what the shape does.
What it boils down to is an effect on airflow from a rapid change in direction. Air moving into an opening has to come from all around when moving into the inducer(or throttle body). In doing so on a normal stright or even slightly tapered inlet, the air must change direction to enter the opening. Doing this obviously slows velocity greatly as if disturbs the boundary layer at the opening(stationary air layer) that affect air friction. It also creates turbulence as the air cannot simply come up over the inlet lip and smoothly shift 180 degrees back into the inlet.
(IMG:http://i123.photobucket.com/albums/o...six/induce.jpg)
A velocity stack essentially allows a progressive transition of airflow direction from the outside end airflow without disturbing the boundary layer(which keeps up velocity) and reduces air turbulence. On NA vehicles properly tuned velocity stacks will yield a drastic increase in low end torque and throttle response. just like in runner tuning length, tuning the length of the stack affect the torque curve of the engine and MUST be carefully planned out.
On turbocharged engines, preturbo stacks do NOTHIING to affect engine torque and power directly. NOTHING. What they do is affect the incoming air to the turbocharger and help the turbocharger work at low CHRA speeds and make it more efficient. This can lead to an increase in power as the aircharge coming out of the turbo tends to be cooler(inducer leading edges are not "slapping" the air as much as they would normally be). These are normally used on large low speed compressors(like a GT30 or larger). Just as in the Na setups they are tuned for a specific RPm range, and in this case that RPM range is for the rotating assembly of the turbocharger, not the engine itself. You'll notice a different torque curve rather than an overall increase in power. The usually lead to a steeper torque curve and a lower CHRA speed on the compressor map, which overall translates to a lower engine RPM as well. High spooling small turbos spin up so fast they normally don't benefit from this. In some instances, like on highly tuned GTP car, where you're running a small turbo at extreme PR's(3+) velocity stacks can and are utilized to tune the entering airflow at that flow level, where the turbocharger is operating at it's max. This though requires extensive dyno and flow testing....tens of thousands of dollars worth to come to a solid setup
Overall you can benefit from one, but don't believe all the hype surrounding them. They do work but the ones that REALLY work cost thousands and are specifically tuned for certain application and operating range.
They benefit NA cars more than turbocharged setups. You'll gain a bigger benefit from stacks in your intake plenum at each runner, that you will at the turbo inlet....
Hope that helps. Ask me any questions if needed......"
from: http://aseclub.net/forums/index.php?...&#entry1181320
and here are some links to places I found them for relatively cheap (besides ebay...not sure if ebay products have the r&d necessary.....)
http://www.turboneticsinc.com/produc...category_id=19
http://www.velocity-of-sound.com/vel...bellmouths.htm
They do look gangstur either way"Seems like ASEC is getting some good old technical question here lately (IMG:style_emoticons/default/icon_wink.gif)
Ryan, velocity stacks change the airflow as exactly stated. They increase the overall velocity of the moving air going through the body. The wikpedia page shows in basic terms what the shape does.
What it boils down to is an effect on airflow from a rapid change in direction. Air moving into an opening has to come from all around when moving into the inducer(or throttle body). In doing so on a normal stright or even slightly tapered inlet, the air must change direction to enter the opening. Doing this obviously slows velocity greatly as if disturbs the boundary layer at the opening(stationary air layer) that affect air friction. It also creates turbulence as the air cannot simply come up over the inlet lip and smoothly shift 180 degrees back into the inlet.
(IMG:http://i123.photobucket.com/albums/o...six/induce.jpg)
A velocity stack essentially allows a progressive transition of airflow direction from the outside end airflow without disturbing the boundary layer(which keeps up velocity) and reduces air turbulence. On NA vehicles properly tuned velocity stacks will yield a drastic increase in low end torque and throttle response. just like in runner tuning length, tuning the length of the stack affect the torque curve of the engine and MUST be carefully planned out.
On turbocharged engines, preturbo stacks do NOTHIING to affect engine torque and power directly. NOTHING. What they do is affect the incoming air to the turbocharger and help the turbocharger work at low CHRA speeds and make it more efficient. This can lead to an increase in power as the aircharge coming out of the turbo tends to be cooler(inducer leading edges are not "slapping" the air as much as they would normally be). These are normally used on large low speed compressors(like a GT30 or larger). Just as in the Na setups they are tuned for a specific RPm range, and in this case that RPM range is for the rotating assembly of the turbocharger, not the engine itself. You'll notice a different torque curve rather than an overall increase in power. The usually lead to a steeper torque curve and a lower CHRA speed on the compressor map, which overall translates to a lower engine RPM as well. High spooling small turbos spin up so fast they normally don't benefit from this. In some instances, like on highly tuned GTP car, where you're running a small turbo at extreme PR's(3+) velocity stacks can and are utilized to tune the entering airflow at that flow level, where the turbocharger is operating at it's max. This though requires extensive dyno and flow testing....tens of thousands of dollars worth to come to a solid setup
Overall you can benefit from one, but don't believe all the hype surrounding them. They do work but the ones that REALLY work cost thousands and are specifically tuned for certain application and operating range.
They benefit NA cars more than turbocharged setups. You'll gain a bigger benefit from stacks in your intake plenum at each runner, that you will at the turbo inlet....
Hope that helps. Ask me any questions if needed......"
from: http://aseclub.net/forums/index.php?...&#entry1181320
and here are some links to places I found them for relatively cheap (besides ebay...not sure if ebay products have the r&d necessary.....)
http://www.turboneticsinc.com/produc...category_id=19
http://www.velocity-of-sound.com/vel...bellmouths.htm
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Re: Turbo bellmouths/velocity stacks
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chawklit rain
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Oct 29, 2007 09:23 PM
