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Velocity stacks

  • Thread starter Thread starter doctorgonzo
  • Start date Start date
D

doctorgonzo

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Not sure I want to go this route, BUT...
My bike came with the pods I have on it, so I never had to figure out the sizing. What size would I need for BS34 carbs? The 34mm is the OTHER end of the carb right?
 
doctorgonzo said:
Not sure I want to go this route, BUT...
My bike came with the pods I have on it, so I never had to figure out the sizing. What size would I need for BS34 carbs? The 34mm is the OTHER end of the carb right?
Click to expand...
Is this a bike you ride everyday? In all weather? If so, you DONT want velocity stacks. if pods are bad in the rain, velocity stacks are death. There is NOTHING preventing them from sucking water into your motor, and that can perhaps lead to hydrolock. Which is death. Plus, even if you DIDNT ride when raining, there is still the fact that, aside from the little screen things, which stop big stuff, there is nothing preventing bits of dust, sand, road grime and anything else from being sucked in there. There was a thread about this not too long ago, where someone posted about seeing the inside of the bores in a motor that had been fitted with velocity stacks for a long time. The cylinders were scored from crap being scraped against them by the pistons. Dunno how true that is or whatever, but something to consider. *I* am hopefully soon going to be fitting velocity stacks to the cafe, BUT, thats not a bike that will get ridden every day, and certainly not in the rain, lest i had a deathwish...lol
 
I wouldn't get to hung up about velocity stacks and bore damage unless you live in a dusty / sandy climate. My mate's A10 has run with stacks on for about 50 years and has done a lot of miles (unkown how many but a bucket load). Still on original bores and doesn't burn oil excessively.

These look nice and are meant for your bike I think (I'll leave you to translate though to make sure!)

http://cgi.ebay.de/Ansaugtrichter-E...ryZ86748QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
 
FWIW the stock airbox incorporates velocity stacks. The boots that connect the carbs to the box have a special shape designed to reduce the effects of pulsing from one carb to another. By lifting the pulses high away from the throat of the adjacent carb it improves performance.
 
duaneage said:
FWIW the stock airbox incorporates velocity stacks. The boots that connect the carbs to the box have a special shape designed to reduce the effects of pulsing from one carb to another. By lifting the pulses high away from the throat of the adjacent carb it improves performance.
Click to expand...
Correct, the stock airbox does incorporate velocity stacks. However, the filter comes first, then the stacks to smooth the airflow induction to the carb. All of this of course is sealed off. *MY* bigger worry in using the stacks on an everyday bike is the effects of the weather on them. They are obviously not sealed, and rain could prove to be a major problem for them.
 
The style of K and N pod I run doesn't seem to have the velocity stack incorporated into it. I may be wrong though. It goes from small at the back to big at the carb.
 
doctorgonzo said:
The style of K and N pod I run doesn't seem to have the velocity stack incorporated into it. I may be wrong though. It goes from small at the back to big at the carb.
Click to expand...
They may be INSIDE. I read somewhere that some of the KN pod models incorporate the velocity stacks as well. The stock airbox when you look inside have the stacks, tho made of plastic or rubber or something, built in.
 
The role of velocity stacks as I understand it:

When the inlet valves shut the inrushing fuel/air mix hits the back of the valve and 'bounces' back. Some of this is ejected out of the back of the carb. Stacks are designed to capture and hold this rejected load and recirculate it back into the carb on the next cycle. If your run with stacks on then remove them and just run with open carbs, you'll see a marked weakening of the mixture.

The standard airbox does indeed contain simply constructed velocity stacks. These are one piece with the airbox to carb rubbers and for a cheap DIY job you could remove the airbox from around them and you would effectively be running with stacks.

By the way - we traditionally call them 'bellmouths' over here.
 
Intake manifold pulses travel back through the carb when running. Since gas will flow no matter which way the wave travels, the velocity stacks keep the standoff from migrating to another carb. Airflow straightening is important too as it presents a uniform pressure to the entry of the venturi. Without the stacks or another way to organize the induction there is interference between the carbs and loss of efficiency.

This is all well documented in Holley Carbs and Manifolds, an excellent reference on carbs if there ever was one. Our systems are very similar to formula 1 cars in operating range and HP/liter output
 
Good info guys. I'm going to research my pods and see if K&N considers them to have "velocity stacks" incorporated into the design. I'm sure on some level they do. I'm just looking for maximum airflow this side of forced induction.
 
Your original question was along the lines of what size K&N's to order for your bike. Try APE. According to Jay they have US made oiled gauze filters like K&N's for a lower price. They also have K&N's and they'll know what size. Don't run velocity stacks. They make air filters for a reason.
 
RJ said:
Your original question was along the lines of what size K&N's to order for your bike. Try APE. According to Jay they have US made oiled gauze filters like K&N's for a lower price. They also have K&N's and they'll know what size. Don't run velocity stacks. They make air filters for a reason.
Click to expand...

Already has k&N pods on it. Considering velocity stacks as an alternative or for sometime use if the same jetting is broad enough to use for both. My digital calipers get here today, so I will be able to measure the OD and see if APE has them.
 
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Yep, OD on BS34 is 55mm, that's the same as the 36 RS carbs, so APE has stacks.
 
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