Topic: adding foam to velocity stacks

[greenjeans]

My pops has volunteered to make me some velocity stacks for my "poor man's" CR750 replica

So, to make them a bit more friendly to the inside of the engine, we were contemplating using 2 screens
1 on the inside and 1 on the outside and fashing some foam which could then be oiled for better cleaning
in the middle....

Any idea of what type of foam we could use, that could be cut to fit the inside of a velocity stack ?
And where we might get some ?

[hymodyne]

When you find out, I'll be very interested; I have stacks on my bike with only a fine brass screen. I'd like to add at least a thin layer of foam to increase the trapping of schmutz before it can get into my carbs...

hym

[Gordon]

I just typed "velocity stacks foam" in the search field and came up with several threads on the subject. 

Not saying you shouldn't ask, but thought you might be able to benefit from the previous work of others.

[eurban]

This has been gone over before.  Installing foam will negate any performance benefits that you might get from running velocity stacks so don't do this if you are looking for performance.  If you are in it for the looks then you could probably buy a few foam lawn mower air filters at the local hardware store.  My Lawnboy mower used to use someting like a 4" x 6" x 1" foam filter block that could be cut to make a couple of velocity stack inserts.  I am also sure you could buy larger quantities of air filter foam online.

[hymodyne]

I typed the same three words into the search field and only got the three posts of this thread...

[eurban]

The regular search function seems to be a bit funkyas of late. Try going to the advanced search option first. I searched under "velocity stack" in the advanced search and came up with lots of hits.  Here's a recent one dealing with this subject
http://forums.sohc4.net/index.php?topic=31872.15

[Gordon]

I typed the same three words into the search field and only got the three posts of this thread...

That's probably because you only searched in this thread.  Try the same thing from the main page.

[dakeddie]

According to David Vizard, tuning guru for Austin Minis, putting foam in your velocity stacks will result in terrible flow... there just not enough surface area on the filtering medium.  He tested this on a flow bench.  It will surely flow worse than the stock airbox.

And screens don't do much for filtering out dust.

Velocity stacks are the ultimate in performance though, it's too bad they don't fit well inside K&N's.  If I were you, I'd put K&N's on for regular riding, and velocity stacks if you're going to show the bike.

[hymodyne]

duly corrected...

I wasn't aware that the search engine operated differently from different links...

hym

[greenjeans]

This bike is truthfully more for show than go...that's not to say that it won't be ridden.
Basically I want the "looks" of a velocity stack combined with the protection of an oiled or stock filter.
I don't really want the hassle of changing between a true velocity stack and pod filters etc.

I've looked through some past posts and found some good stuff, but I was looking mainly for a source of a foam
that could be shaped to fit inside the stack betweeen some screens... Hadn't even thought of a lawn mower filter....
That will be worth a try.  Every question has been asked before, and sometimes it doesn't always yield the same answers.  Somebody has usually already solved my problem/question and it can be easy to miss reading through post after post of similar answers...thus breading my general lazyiness on searching and searching.  I know I'm contributing to my own problem and believe me, I'm trying not to ask so many questions - but is addictiing knowing you can post a question and have a wealth of answers and knowledge in such a short time.

I'm going to give the lawn mower filter a shot & I'll post the results. 

At least I haven't asked about jetting for them

[heffay]

BAH!  if you're gonna run stacks... run em!

[sparty]

You are wasting your time and money putting foam in those stacks.  You bike will run like crap.  These engines need to breathe.  There is a good reason they don't make foam for stacks.......  it does NOT work well.  You will also foul the plugs as it will run richer.  You can mess with jetting all day and it won't make a difference.  Running like crap is running like crap.  But don't listen to us, find out for yourself.  Then we can say "Told you so".

Sparty

[mystic_1]

At least we have it easy, stacks on a CB face backwards.  A lot of harley guys run with velocity stacks that point forward, like a giant funnel for channeling dust, rocks, birds, and so forth into the carb 


mystic_1

[greenjeans]

ok...ok ..... maybe I'm a bit stubborn  - I've found a couple on here that have had success with filtering material

[Sam Green Racing]

 

[754]

Dont be a pussy.. run em open..

You already said more show than go..


 Running filters on stacks is  like taking your Mom along when you go on a date..

[hapsh]

Running filters on stacks is  like taking your Mom along when you go on a date..

 


The stock airbox has velocity stacks inside the rubber airbox boots.  Oh, oops, you can't see them, shoot.
I would do what others suggested, run the stacks without any filters, just screens.  I have known several guys over the years that used to run their bikes without any filters at all and had no problems.  Yeah, if you commute 40 miles a day on the interstate, I would think otherwise.   But just cruising around here and there I would not worry about it.  You think its a pain jetting for pods, try jetting for a chunk-o-lawnmower airfilter foam 2" thick.

[heffay]

i'd have no problem running stacks on the interstate... its around town, especially near windy construction sites or dusty parking lots and roads.

[dakeddie]

This bike is truthfully more for show than go...that's not to say that it won't be ridden.

Just run the stacks... it looks wicked.  Doesn't look bad with the oiled screen too.

[greenjeans]

That's it then....no filters just the fine mesh screen.  My commute is only 1.5 miles.

[hahnda]

I can't comment on how the bike runs with them yet.

[greenjeans]

Like 'em - where'd you find them ?

[hahnda]

Dont know. They were already on there.

I do have another set of stacks though and they use something similar to hold the screens on. In the pic its just real thin foam over the screens. I guess the key is having those round holders that go over the "bell".

[heffay]

for the sake of answering your question... 

i've heard of womens' hosiery working as a 'sort of' filter
at least better than a screen door type screen

if they were my stacks... i'd only run screen or nuthin... but you knew that.   

[Geeto67]

I have a set of old circycle V-stacks that came with filters and foam. I replaced the crumbly foam with pieces of foam from a unifilter. Works fine, never had a problem on that bike because of stacks.

[KeithB]

If this is an "all show no go" bike then ignore this post.
However, if you actually are looking fo the go, then run them open or just coarse screen.
The whole point of a properly tuned stack is to improve the air flow characteristics to the carb for better performance.
To actually be effective they need to be tuned for the carb settings and exhaust system.
To put and air filter in the way of the incoming flow seems counter productive.
These are generally used on the track where high performance for  short periods is needed and engine re-builds are common.
Might as well use pods.
Just my $.02 worth...

[greenjeans]

To be honest, It would probably only get about 15-20 miles during the week total (short commute)
with the occasional weekend ride to shows etc.  Usually once in the summer I'll take a trip on
it (still, not more than about 250 miles or so) and realistically that's about it.  No trips to the
track, mainly just short cruises....probably spend more time warming her up than riding.
Just always love the looks of a velocity stack.  I'll start by running the fine mesh screen and
maybe I'll experiment with some thin foam...who knows. 

[James]

Running filters on stacks is  like taking your Mom along when you go on a date..

In some places they are the same person

Be mindful that there is a hell of a lot of suck going on at the stacks, a pal o mine put some foam over the stacks and after his first ride found some nice neat holes in the foam, the bike still ran, but I'm not sure that it did it any good.

I would say put a metal screen between the foam and the carbs to give it a bit more integrity!, or get some proper K&N foam, not just household stuff.

[eldar]

How fine are your screens? I mean if they are not that fine, Get some different screen material that has smaller openings. Still wont filter like foam or paper but will stop some smaller stuff.

[754]

I actually think fine screen would be quite restrictive...

The main problem is lack of area to filter, unless you use very thin foam and a coarse screen, after a point the overall flow gets reduced. and I dont think thin foam will stop everything.

Here is another example, I took the ends of UNI filters or other such foam, put it over the aircleaner end of CB350 carbs..it was so restrictive it barely ran.. so the bigger the aircleaner the easier it breathes. I was sa bit surprised when the first tapered K&N's came out, still dont know if it was for less interference on the outer end or for turbulence reasons of airflow past the outer aircleaners.

In my mindseye, I see this with very fine screen.. imagine pasta being pushed thru a fine screen.. as it comes out the other side it would be all squiggly and curling  and twisting.. anything but straight. This is what I am thinking happens to the air when it hits the screen.. instead of a smooth coloum of air entering it is a jumbled mess of a thousand small coloums of air trying to straighten out and join together.

But the screen will keep flies out!!

It takes quite a while to wear out the topend on an unfiltered motor.. unles you live in extreme dusty conditions..longer than you may think..

[goon 1492]

I actually think fine screen would be quite restrictive...

The main problem is lack of area to filter, unless you use very thin foam and a coarse screen, after a point the overall flow gets reduced. and I dont think thin foam will stop everything.

Here is another example, I took the ends of UNI filters or other such foam, put it over the aircleaner end of CB350 carbs..it was so restrictive it barely ran.. so the bigger the aircleaner the easier it breathes. I was sa bit surprised when the first tapered K&N's came out, still dont know if it was for less interference on the outer end or for turbulence reasons of airflow past the outer aircleaners.

In my mindseye, I see this with very fine screen.. imagine pasta being pushed thru a fine screen.. as it comes out the other side it would be all squiggly and curling  and twisting.. anything but straight. This is what I am thinking happens to the air when it hits the screen.. instead of a smooth coloum of air entering it is a jumbled mess of a thousand small coloums of air trying to straighten out and join together.





     Actually from my learning experiences the small columns will help orientate the air flow unless like you said using too small of a screen , it is even worse of an effect like what your describing that happens with regular air filters, they filter the air but it all gets churned up going thru the filter. That is why honda put the stacks inside the box after the filter, and the true purpose of a velocity stack is to condense the air, if you think about it you take the air space of a large opening in a pipe and force it thru a smaller opening at the other end of the tunnel the air becomes compressed giving you a little more compression in the combustion chamber. These stacks are so small they probably don't have that much of a performance effect there's not much area to scavenge large ammounts of air.  I'm not sure if many people remember the the good ol' monster ram air intakes with 6in tall stacks on top of a monster flat head v-8....... man that's good times

[eldar]

Ok so modify things so there are scoops on each side with the screen at the front about an inch after the opening. It will filter some and then the air can smooth out before going into the filter..

But a person never knows till they try. After all, look at how many things were supposedly impossible and are now everyday things. But I cant tell anyone to not assume things just cause they do not think it will work.