No Velocity Stack!

A velocity stack has to be one of the coolest-named parts that I am never going to put on any of my bikes. I do have a question, though.

I saw this bike on Pittsburgh craigslist; once upon a time it was a Honda 550, and now has a velocity stack on each of its carbs. I've seen discussions here about putting one on a moped carb.

So far, the best description of its intended purpose I've gotten is that a velocity stack smooths the airflow into the carburetor.

So, question: I can see that on a bike like the 550 above, two carbs pulling in a huge amount of air could cause turbulence near the intake, and decrease performance. It seems that if you have that much airflow, though, you're going to be sucking up other stuff too - leaves, twigs, rocks, dust.

Wouldn't you want to put a velocity stack inline with a large capacity air filter? I imagine that a bike's restrictive stock filter would make the velocity stack worthless, but what if you put on a huge ring filter (like one from a car) - wouldn't you still see the same performance gain (if any) without getting stuff in your engine?

Re: No Velocity Stack!

I made some for bings, they work amazing. Improvemnet seen mostly at low to mid range.

It did however suck up tons of shit as the vacum was huge (needed to up-jet); i was using window screeening as a filter which is too coarse. I've since found a finer mesh that matches clsoely what's on a Mikuni factory v-stack i just haven't had time to rig it up.

What I think would work best is a v-stack w/a big uni-pod/K&N on the end.

Attached is a pic...


Re: No Velocity Stack!

Please dis-regard my horrible spelling in that last one, clicked a little to the right...

Re: No Velocity Stack!

ive got a velocity stack on my joint. pulls really hard, makes a mean sound...but yeah sucks up alot of shit. def better performance than the plastic snail shits on phbg

Re: No Velocity Stack!

yeah and you have to upjet like crazy

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you can also tune the length of them to buddy with your exhuast

Re: No Velocity Stack!

From what i remember reading a few months back is that you want it tuned to match the exhaust as much as possible; if you're good at math do it.

As a general rule of thumb the longer the stack the lower your power-band will be, and the shorter the stack the higher up it will be. So short stack + short header should = more top-end; and long stack + longer header should = better low-end.

Re: No Velocity Stack!

its not so much about smoothing the air, as creating a postive pressure gradient and dampening the dynamic sonic effects on the carb (hence the larger jet). i've explained what they do and how to size them... you can do a search for it.

in non engineer-speak

'cone thingy good'

Re: No Velocity Stack!

I like what Derek said - that's sort of where I was going with this.

If you have to tune the size of the velocity stack to the size of your exhaust system (or the back-pressure of your exhaust - I didn't quite see which), couldn't you also tune the stack for the inclusion of a beefy air filter?

So, if you put an air filter at the end of a velocity stack, you would restrict airflow and ruin the effect. However, if you made sure to allow for the extra length of cone-thingy (thanks Graham), and widened the end of the cone to account for the extra resistance of the air filter, it almost seems like you could work towards all of the benefits of the velocity stack without any of the detriments.

I'm tending less towards actually considering this as a performance mod, and more towards wondering why the insides of aftermarket air filters aren't hyperbolic-cone shaped.

Re: No Velocity Stack!

Bruce Edwards /

"I’m tending less towards actually considering this as a performance mod, and more towards wondering why the insides of aftermarket air filters aren’t hyperbolic-cone shaped." Very good question!

Re: No Velocity Stack!

i looked, mine has it, my fa 50s air box tube gets bigger at the end not much of a difference but enuf to make it only go on one way and to suck in air

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I'm bringing my bing one to KZoo if any wants to see/try it; just find me...

Re: No Velocity Stack!

That velocity stack looks like the bell from a clarinet!!! It looks wicked though. I bet it works good

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