 Volocity stack design considerations??, for my mickey mouse ITB's |
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| Mueller |
 Apr 4 2006, 03:19 PM
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#1
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914 Freak!  Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None 
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Slightly warmed up /4 motor applications...I'm thinking just about any design better than none at all....I'd like to metal spin these myself, however if I can get a good price on 8 from a fellow non-club member, I'll go that route (IMG:http://www.914world.com/bbs2/html/emoticons/smash.gif)
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Replies(1 - 19)
| bd1308 |
Apr 4 2006, 03:42 PM
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#2
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Sir Post-a-lot Group: Members Posts: 8,020 Joined: 24-January 05 From: Louisville,KY Member No.: 3,501 |
carbs have had velocity stacks for years....
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| spunone |
Apr 4 2006, 03:52 PM
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#3
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Senior Member Group: Members Posts: 945 Joined: 6-April 04 From: Anaheim CA Member No.: 1,901 Region Association: Southern California |
Just send me the measurements and if we ever meet up you can buy me a few (IMG:http://www.914world.com/bbs2/html/emoticons/beer.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/beer.gif) no need to try it yourself unless your really bored (IMG:http://www.914world.com/bbs2/html/emoticons/av-943.gif)
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| spunone |
Apr 4 2006, 04:04 PM
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#4
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Senior Member Group: Members Posts: 945 Joined: 6-April 04 From: Anaheim CA Member No.: 1,901 Region Association: Southern California |
You can roll outer edge back onto itself I have made a few like that or just the straight edge like your pic how close togeather are they you may need to notch edge and weld just some ideers
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| SirAndy |
Apr 4 2006, 04:14 PM
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#5
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Resident German Group: Admin Posts: 41,671 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California |
make 'em longer. much, much, much longer ... torque is what you want, right? (IMG:http://www.914world.com/bbs2/html/emoticons/rolleyes.gif) Andy PS: if you get my axle done, i'll give you these for free! (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) 2 3/4" high, set of 4 Attached image(s) 
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| jsteele22 |
Apr 4 2006, 04:27 PM
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#6
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Senior Member Group: Members Posts: 727 Joined: 24-August 05 From: Colorado Springs, CO Member No.: 4,653 |
Hey Mike,
Don't know if you've run across this, but this page at SDS EFI describes making velocity stacks by machining a form out of steel, then pressing the stacks over the form with a hydraulic press. Might be a nice way to go if you're thinking of producing multiple units... Are you planning on having the stacks out in the open or inside a plenum ? |
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| ClayPerrine |
Apr 4 2006, 04:38 PM
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#7
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Life's been good to me so far..... Group: Admin Posts: 15,505 Joined: 11-September 03 From: Hurst, TX. Member No.: 1,143 Region Association: NineFourteenerVille
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| ClayPerrine |
Apr 4 2006, 04:40 PM
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#8
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Life's been good to me so far..... Group: Admin Posts: 15,505 Joined: 11-September 03 From: Hurst, TX. Member No.: 1,143 Region Association: NineFourteenerVille
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| ClayPerrine |
Apr 4 2006, 04:41 PM
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#9
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Life's been good to me so far..... Group: Admin Posts: 15,505 Joined: 11-September 03 From: Hurst, TX. Member No.: 1,143 Region Association: NineFourteenerVille
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If you are really pimpin'. you would use these....
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| Mueller |
Apr 4 2006, 05:14 PM
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#10
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None
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uh, thanks for the history lesson..I think (IMG:http://www.914world.com/bbs2/html/emoticons/screwy.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)
so far, t/b's have cost:
*he paid I think $200 or so for his motorcycle t/b's which I am modifing as well... Andy, One end of the axle is done, just need to do the other one, tonight I'll try to get it done. Diameter is critical..... Paul, I can send you a real drawing if I can get my computer from crashing due to new video card (IMG:http://www.914world.com/bbs2/html/emoticons/headbang.gif) So far... "A"...minimum ID to be 47mm, max OD 55mm (I doubt you'd use .156 or thicker material (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) ) "B" 90mm before overlapping "C" whatever R is easy for you, nice big one will work for me (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) Overall height, I'm thinking somewhere between 2" and 3" due to aircleaners, unless I can find a nice tall aircleaner (something smaller than the 9" units I've seen at the bug places) Attached image(s) 
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| Thorshammer |
Apr 4 2006, 09:05 PM
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#11
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Senior Member Group: Members Posts: 749 Joined: 11-November 03 Member No.: 1,335 |
The outer lip needs to be rounded. The edge is very important to good airflow. I have some stacks that are length adjustable for webers that I will be making in the next couple months. Not sure if you can wait. Erik Madsen |
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| retrotech |
Apr 4 2006, 09:48 PM
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#12
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retrotech Group: Members Posts: 470 Joined: 2-November 03 From: Mosier, Oregon Member No.: 1,302 |
I tested air flow with vacume cleaner suction & smoke, on standard sharp edge velocity stacks, versus rounded/rolled edge. The air flowed significantly better with the rounded edge. It was really difficult for the air/smoke to travel freely around that hard edge.
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| Twystd1 |
Apr 5 2006, 12:43 AM
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#13
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You don't want to know... really..... Group: Members Posts: 2,514 Joined: 12-September 04 From: Newport Beach, California Member No.: 2,743 |
YUP... What everybody else said about the rounded edge.
He Paul.. I know you have made these before. Can ya make a clone of the TWM style rounded edge stacks?? Word is from the head porters I know, that is the correct shape (or close to it) One guy flows heads with the complete intake system attatched. He say's the rounded edge doesn't really give them much more CFM. But it does give them more uniformity of flow. Especially on carbs. Cause carbs need the velocity and proper flow charachteristics to get the fuel sucked out of the transition ports and the center anular ring effectively. They say it makes a great differance on transition from idle to mid or full throttle. (on carbs) Other than that.. I don't know any real data... By da way... take a look at those factory RACE ENGINES that were at the Pelican auction a couple of weeks back... (pics at PP board) ALL velocity stacks were rounded over. Paul.. You and I looked at em at the swap meet... Clayton |
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| Porcharu |
Apr 5 2006, 02:09 AM
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#14
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Senior Member Group: Members Posts: 1,314 Joined: 27-January 05 From: Campbell, CA Member No.: 3,518 Region Association: Northern California |
Get that mill going Mike. Make an insert and press or pound it into some dead soft aluminum, my college roommate did this and made some very nice parts. You could also go low tech and just mill some MDF radiused inlets - it works just fine.
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| jsteele22 |
Apr 5 2006, 11:28 AM
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#15
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Senior Member Group: Members Posts: 727 Joined: 24-August 05 From: Colorado Springs, CO Member No.: 4,653 |
I don't know anything about the design of velocity stacks, but that ain't gonna stop me from spouting off....
I think Twystd1 is right : the place where stack design matters most is for carbs, 'cause the detailed behavior of the air flow determines how much fuel you get from the venturi, and also how well the fuel/air get mixed. Since F/I handles these two issues very reliably, you mainly want to keep the flow from going turbulent : laminar flow (where air flows smoothly in layers parallel to the tube walls) will get you more air, so more power. My guess is that using *any* sane velocity stack profile will get you like 80% of the way there, and the only thing to get you to the ideal is gonna be trial and error, and/or massive amounts of computer modelling. If there is no velocity stack, only an abrupt open tube end, then when a "vacuum pulse" reaches the top end of the pipe, it's gonna want to draw air in from every direction. Air directly above the pipe will flow right in, but air that is directly to the side of the pipe is gonna have to make an infinitely sharp 90 degree turn if it's gonna follow the tube wall. Since it can't, it's gonna understeer and separate from the wall, giving rise to turbulence. Adding a bell shape does (at least) two things. It gives the air thats out to the sides of the stack a nice gentle curve to follow as it goes from flowing sideways to flowing downward. This in itself reduces the likelihood of turbulence. But the area of the tube opening is also made quite a bit larger. Twice the area means that the air is traveling half as fast as it enters. Then add to this the fact that air travelling along the tube walls is gonna travel much more slowly, due to friction, than the air flowing down the center. So the outer part of the flare is like a landing pad/slow lane for getting the most problematic air flowing in a nice oderly way side by side with the bulk of the air which is coming from the more vertical directions. As for the rounded lip issue, yeah its got to help some, in theory, but I think that by the time you get out to the lip the air velocity along the bell surface is pretty small, so it's really gonna be a hair-splitting kind of issue. If you were going for massive HP (i.e. massive air flow) then it might be worth doing. But for this project, I can't see it showing up on the radar. All of the above (besides being pure speculation on my part) only describes the steady-state behavior. In the intake, you're really looking more at pulses of negative/positive pressure superimposed on top of this. I've heard, and it makes some sense, that another thing velocity stacks accomplish is to broaden the torque peak. |
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| maf914 |
Apr 5 2006, 01:31 PM
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#16
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Not a Guru! Group: Members Posts: 3,049 Joined: 30-April 03 From: Central Florida Member No.: 632 Region Association: None
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Lot's of good ideas, but how come no one has mentioned carbon fiber? That would make it a lot faster! (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif)
Actually, when you wander around the paddock at sports car and formula car events, most of the newer racing engines use carbon fiber horns, and the outer lips are quite rounded. These are all injected engines but obviously the consensus is that rounded is better. All of this is typically hidden in a sealed airbox feed through one or two air restrictors. |
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| Mueller |
Apr 5 2006, 01:38 PM
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#17
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None
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they are pretty aren't they ??? (IMG:http://www.914world.com/bbs2/html/emoticons/wub.gif) (IMG:http://www.twminduction.com/AirHorn/AirHorn.imgs/carbon_horn_2_lg.jpg) |
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| Aaron Cox |
Apr 5 2006, 01:43 PM
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#18
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
yummy jenevey's (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)
(IMG:http://www.jenvey.co.uk/Imgs/Accs/AHc_m.jpg) |
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| Aaron Cox |
Apr 5 2006, 01:44 PM
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#19
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Professional Lawn Dart Group: Retired Admin Posts: 24,541 Joined: 1-February 03 From: OC Member No.: 219 Region Association: Southern California |
OMG! they even make "injected air horns"!!! like that would be uber cool!
(IMG:http://www.jenvey.co.uk/Imgs/Accs/AH51x125IM.jpg) |
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| Mueller |
Apr 5 2006, 01:50 PM
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#20
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None
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