Topic: Velocity Stacks & filtering?

[dummkauf]

Is this possible?

I am in the process of rebuilding my carbs and I love the look of velocity stacks on a bike, however I am concerned with the air filtering ability of velocity stacks.  Every velocity stack I've seen for sale looks like someone just glued a screen onto the end of which while great for keeping sticks and small animals out of my engine, doesn't look like they will do much for keeping dirt out.

I have been toying with the idea of taking a K&N filter and trying to cut it down and retro fit the pieces into a velocity stack, however since most K&N pods are huge compared to a velocity stack I'm not sure if the little pieces of filter would allow enough air flow, as well as I am still unsure on exactly how I would accomplish this either way.  Ideally I would want the filters recessed into the stacks if possible so they are not visible.......so basically I want form & function if at all possible 

I did some searching on this site and the interwebs and couldn't find anything on this.  It appears that unless I make something myself I am left with 2 options.
     1) Velocity Stacks which = poor filtering
     2) Pods or Airbox = best filtering

So my questions to all of you knowledgable folks are:
    - Are there any velocity stacks available for my carbs that have a quality filter builtin?
    - Would cutting down a K&N filter and somehow fitting it into a velocity stack allow enough airflow?
    - Since I am in the middle of my carb rebuild....what sized jet should I be going to for velocity stacks(or filtered stacks )?

Oh, and I have stock keihin carbs on a 76' CB750 K6

[Sam Green Racing]

I think you know the answer to that one

You can't have it both ways, one idea cancels the other out.

Sam.

[Joel]

It is possible to buy foam material for custom applications.  You could fit a chunk into the stack and use a screen over the end to hold it in.

http://www.unifilter.com/online%20catalog/accessories.html

[scunny]

if you want to put foam in the stack, have a gauze filter between the foam and your motor(stops sucking it in)
what Sam said, foam filters and stacks don't match. choose one or the other.

[ieism]

A filter in a stack will seriously upset airflow, and defeats the purpose of a stack. In fact, those grills to stop the rabbits getting sucked into your carbs are already a very bad idea on velocity stacks.

There was a discussion about making a short velocitystack INSIDE a k/n filter here for a while. That seamed like a good idea. But I have K/N filters, and don't see how you could get a stack in there, you'd have to saw it in half.

[dummkauf]

There was a discussion about making a short velocitystack INSIDE a k/n filter here for a while. That seamed like a good idea. But I have K/N filters, and don't see how you could get a stack in there, you'd have to saw it in half.

I don't understand the point of the stack inside the filter?  What possible benefit would that provide?  Atleast to me it seems that would reduce airflow since the stack would be effectively reducing the amount of air flow to the engine that the filter would provide without the stack inside of it?

I'm not going to try this, but I am curious what the reasoning behind this is.

[dummkauf]

Another question to all of those out there that are running velocity stacks:  How long do you run before needing to clean your motor out?

Or would I be correct in thinking that velocity stacks are generally saved for show or race bikes that are not driven very often?  When I am done with this project I have no intention of using the bike for my daily commuter(I have a 70mpg thumper for that ), however I do plan on driving it on a regular basis.  My weekend rides can easily take up an entire day.

[scunny]

ran stacks on my 500 for about 2 years, some roundies,drags and to work every day. never had a problem. obviously wear will be increased(don't do dirt roads)

[Sam Green Racing]

Another question to all of those out there that are running velocity stacks:  How long do you run before needing to clean your motor out?

What do you think gets in there that needs to be cleaned out ?

Sam.

[Joel]

I can see how a stack with a filter won't flow as well as one without.  However, is a stack with a filter any worse than a pod filter?

A wire or mesh basket could hold a foam filter element for normal operation and be removable to allow open operation when desired.

[Sam Green Racing]

You would need to keep changing your jetting if you swapped between the two.

Sam.

[dummkauf]

What do you think gets in there that needs to be cleaned out ?
Sam.

I'm picturing dirt, rocks, bugs, and anything else flying around that could get sucked in getting into my motor and causing problems

[Joel]

You would need to keep changing your jetting if you swapped between the two.

Sam.

True, I hadn't thought of that.

[dummkauf]

I can see how a stack with a filter won't flow as well as one without.  However, is a stack with a filter any worse than a pod filter?

This is an excellent question?  Does anyone know?

[scunny]

Sam, he wants to keep rodents out.
during normal use there is not much to worry about. my concern was always people putting things in there so I had bungs to solve that problem
regards filter media, if you look at say a pod filter, the entire(well almost) of the pod is used due to the fact that it reduces air flow, so to counter this you increase the surface area of the filter media. TT would?might be proud of me  

[ieism]

It's not all about increased airflow. Why do velocity stacks always have the "bellmouth" shape?
Why are the intake rubbers on the stock airbox shaped like small stacks?
Why does a bike run better with stacks than without them ?

I don't know the exact science behind it (TwoTired is an expert on this) but it's got something to do with the velocity of the airstream and vacuum.

You can run stacks on a streetbike, but it will slowly sandblast your engine.

[Sam Green Racing]

What do you think gets in there that needs to be cleaned out ?
Sam.

I'm picturing dirt, rocks, bugs, and anything else flying around that could get sucked in getting into my motor and causing problems

Dirt dust and bugs will go right through. Rocks on the other hand
That's why we have fillter or pods for every day use.
Ram stacks are for performance where there is little chance of anything getting in there.
Although a moto crosser is a performance bike, you never see them running in all the sh1t without a filter.

Sam.

[Joel]

The bell shape allows a smoother transition for the incoming air.  Less turbulence allows increased velocity.

[dummkauf]

I think I'm going to end up getting a set of pods.

Stacks would be nice but ultimatley I want my engine to last and be functional, which from this discussion rules out my stacks

[Sam Green Racing]

I think you know the answer to that one

You can't have it both ways, one idea cancels the other out.

Sam.

 

Sam.

[scunny]

Although a moto crosser is a performance bike, you never see them running in all the sh1t without a filter.
bugger there goes another brilliant idea
yep bellmouth is to lower turbulance, check out some of the carb rubbers from filter box to carb, some of these are bell mouthed.

regards as to run stacks or not... if you like the look go for it
                                              if you want to prolong the time between top end rebuilds, don't
 stacks perform best when on the throttle, couple this with a 4 into 1 and you can(sometimes) increase top end performance but sometimes compromise general road use

[dummkauf]

I think you know the answer to that one

You can't have it both ways, one idea cancels the other out.

Sam.

 

Sam.

Yeah yeah yeah.....I'm stubborn and don't give up easily

Thanks for all the input though.  Sometimes bouncing ideas off of others helps to clear up the situation.

[scunny]

they do look good tho 
if it's any consolation I like stacks but am probably going to go pods now because my track days are probably over

[tsflstb]

Stacks are dangerous - there was a small child in that stroller before I fired it up.

[scunny]

ha ha ha..............nice stack