 Volocity stack design considerations??, for my mickey mouse ITB's |
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| spunone |
 Apr 5 2006, 01:50 PM
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#21
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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  |
Ok one more for ya fellas .On a few nitro drag bikes they use a rounded edge stack with a smaller stack say half the size inside of it welded in place with 3 tabs perpendicular to each other.they say this increases air flow about 45% and need to lean it out a shit load from conventional single stack.I myself don't know nuttin just somethings I hear from time to time .Also TRD racing uses Alum round edge stacks about 8 inches long to start put motor on Dyno then they start cutting them down to who knows what size for peak HP on the special race motors Again just something I hear .Glad I gots big ears (IMG:http://www.914world.com/bbs2/html/emoticons/w00t.gif)
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| jsteele22 |
Apr 5 2006, 02:43 PM
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#22
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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 why two stacks would give more airflow, but I guess there's a tradeoff : more surface area causes more drag (bad) but the additional stack does a better job of guiding the air into the tube without tumbling (good). Kind of like going from 16 lanes down to 4 after a toll booth : doing the merges in two steps seems to work a little better. Again, trial and error is probably the primary means to pick the best setup, and if that doesn't work, just go w/ carbon fiber.
About the length, the longer the tube the more air is moving in one direction at the same velocity. Like the marching band in Animal House, once the head of the column reaches a dead end (the piston) the rear of the column keeps pushing forward due to it's momentum. But long tubes also cause more friction, so at high RPMs it's mostly just a hindrance. Since intakes don't run that hot, they can be made out of nice light, workable materials - the "test and chop" method sounds like a great way to go to find the perfect length. Exhaust systems, OTOH, have to be heavy, and therefore are a PITA when it comes to trial and error. It would be so nice to make up a test set of headers and exhaust out of, say, PVC pipe and run for ??? seconds before they melted through.... |
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| john rogers |
Apr 5 2006, 02:49 PM
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#23
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Senior Member Group: Members Posts: 1,525 Joined: 4-March 03 From: Chula Vista CA Member No.: 391 |
Something to think about, are you going to run air cleaner(s) and if so which ones? Or are you going for the tall Hilborn injector Can-Am look? When my race engine was dyno'd taller stacks were used and I had to go to taller filter elements which just about touch the engine cover on the 914 and that is with the enging sitting an inch lower than stock. The taller the stacks, the higher in RPM range all things being equal but for a given cam, head combination there is a stack height for the best power production and mine happened at 7000 RPM with the parts we had.
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| Aaron Cox |
Apr 5 2006, 03:25 PM
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#24
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Professional Tinkerer Group: Retired Admin Posts: 24,548 Joined: 1-February 03 From: Corona, CA Member No.: 219 Region Association: Southern California |
what if you had 4 different size stacks????
(IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif) torque, top end, and mid range LOL |
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| jd74914 |
Apr 5 2006, 03:27 PM
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#25
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Its alive Group: Members Posts: 4,875 Joined: 16-February 04 From: CT Member No.: 1,659 Region Association: North East States |
Or adjustable ones that taper down so they can be collapsed and expanded easily depending on the desired change. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif) |
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| jsteele22 |
Apr 5 2006, 03:28 PM
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#26
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Senior Member Group: Members Posts: 727 Joined: 24-August 05 From: Colorado Springs, CO Member No.: 4,653 |
Well, you'd want some way to select the right one at the right moment. Don't want the switches to look ugly, though. Maybe use ivory, with some shorter ebony ones in between. |
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| Aaron Cox |
Apr 5 2006, 03:29 PM
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#27
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Professional Tinkerer Group: Retired Admin Posts: 24,548 Joined: 1-February 03 From: Corona, CA Member No.: 219 Region Association: Southern California |
wasnt that called active induction? ala growing stacks on a mazda no? got banned in some racing thing for it... |
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| jsteele22 |
Apr 5 2006, 03:42 PM
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#28
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Senior Member Group: Members Posts: 727 Joined: 24-August 05 From: Colorado Springs, CO Member No.: 4,653 |
Actually, the Subaru SVX had some kind of system for altering the intake path. I think it was a flapper similar to a throttle body that was actuated by a vacuum servo to switch between low- and high-rpm modes. THat would be a fun thing to stitch into MegaSquirt one of these days... |
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| bd1308 |
Apr 5 2006, 04:02 PM
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#29
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Sir Post-a-lot Group: Members Posts: 8,020 Joined: 24-January 05 From: Louisville,KY Member No.: 3,501 |
guys, we need to think outside of the box.
I am going to go ask teh UFO guys to see if we could get some primordial goo and train it to morph into a tall, medium and short sized velocity stacks for us. Hey they'd do it for years, just to see Miles--their father. b |
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| TimT |
Apr 5 2006, 04:15 PM
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#30
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retired Group: Members Posts: 4,033 Joined: 18-February 03 From: Wantagh, NY Member No.: 313 |
AKA Varioram used on the latest /6 ers..varies the intake length |
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| Aaron Cox |
Apr 5 2006, 04:18 PM
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#31
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Professional Tinkerer Group: Retired Admin Posts: 24,548 Joined: 1-February 03 From: Corona, CA Member No.: 219 Region Association: Southern California |
what activates it? or... what mechanicly drives it? |
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| TimT |
Apr 5 2006, 04:33 PM
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#32
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retired Group: Members Posts: 4,033 Joined: 18-February 03 From: Wantagh, NY Member No.: 313 |
Let Steve Timmins explain
http://instant-g.com/Products/36Conversion/VRAM.html He is a physics professor at Univ of Del... teaches vehicle dynamics and stuff |
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| Rick_Eberle |
Apr 5 2006, 06:11 PM
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#33
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Member Group: Members Posts: 390 Joined: 14-January 04 From: Geelong, Australia Member No.: 1,558 |
Here's what Suzuki use on their current GSX-R's. The velocity stack is rubber, with slots in the side, supposedly to reduce pulses in the intake. The stack also seals the tb to the airbox.
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| Rick_Eberle |
Apr 5 2006, 06:12 PM
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#34
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Member Group: Members Posts: 390 Joined: 14-January 04 From: Geelong, Australia Member No.: 1,558 |
Showing the slots...
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| maf914 |
Apr 6 2006, 09:15 AM
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#35
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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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Those slots are different. I've never seen that before. Cool! (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) I'd like to read an explanation of the idea behind that design. |
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| maf914 |
Apr 6 2006, 09:21 AM
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#36
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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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In the old Can-Am days almost everyone ran with tall intake stacks. Some engines ran with staggered height stacks. I don't know if this was to deliberately tune various cylinders for different power characteristics or to prevent equal height stacks from stealing airflow from adjacent stacks. Regardless, they looked cool! (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif) |
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| Rick_Eberle |
Apr 6 2006, 06:42 PM
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#37
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Member Group: Members Posts: 390 Joined: 14-January 04 From: Geelong, Australia Member No.: 1,558 |
Here you go... not much detail, unfotunately. GSXR These tb's also have a secondary throttle plate worked by a stepper motor driven by the ecu. It lets them control the velocty into the ports at low rpm, and get back some mid-range. (IMG:http://www.mcnews.com.au/NewBikeCatalogue/2001/Suzuki/GSXRimages/GSXR1000_injector_600p.jpg) That would be cool to run with MS. |
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| J P Stein |
Apr 6 2006, 06:51 PM
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#38
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
From what i've read, the different length stacks were to tune the engine to run as 2 4cyl engines. Apparently, there was a dip in the torque curve that this tuned out.....tho it's hard to imagine an 8+ liter BBC with too little torque anywhere (IMG:http://www.914world.com/bbs2/html/emoticons/laugh.gif) "Some" dyno time to figure that one out, eh? (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) |
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| Porcharu |
Apr 6 2006, 10:42 PM
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#39
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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 |
I think the staggered stacks were to equalize the different port lengths on the big block chevy heads. Those heads have two differently designed intake ports per head. |
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| fin |
Apr 7 2006, 08:16 AM
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#40
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Newbie Group: Members Posts: 47 Joined: 3-January 05 From: MPLS, MN Member No.: 3,398 |
I believe the formula for a proper roll on the mouth of the stack is one fourth of the diameter of the tube.
So a 50mm TB would need a roll of 12.5mm. The different lengths of the velocity stacks was for tuning pairs of cylinders for different torque/HP sweet spots, giving the motor a wider torque band. Once transmissions increased to five or more gears, the designers went back to a narrower and higher torque bands. In the Ferrari museum, I saw velocity stacks with the invector centered in the top and pointing straight down into the intake. Looked very cool. Especially on a single cylinder test motor. CNC lathe would do a better job than a mill, but if that's what you have, make it work! Fin |
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