Velocity stacks and filter heights

[ps2375]

So, currently my IDF's have 2.25" velocity stacks with 3.25" airfilters. Leaving only 1" between them and the lid. I know the underside of the lid is getting "washed" by fuel, because last year when I first got the car back on the road I had plasti-dipped the chrome bases and lids black cause they looked better. I had also coated the insides of them to cover all the chrome edges better. After driving some, when I removed the lids for some reason, the undersides were clean.
Today I went to local VW part shop to ask what was tallest filter I could fit under my deck lid w/o standoffs, nobody had an answer. I was pretty sure that 6" filters would be a no go. So, tonight I made a 1.75" cardboard spacer to see if that and my 3.5" filters would fit, the cardboard was a bit more than the 1.75" and it seems that a measured filter height of 5.25" will just fit on 1/2 side and the same will easily clear on 3/4 side to deck lid(and even clear my engine harness connection above carb on that side).

What kind (if any) benefits can I expect with the added room above the stacks? I know the air will have a better entry into the stack opening, and this will translate to what? Better cylinder filling, better throttle response?? Just looking for a better understanding of what makes a carb tick and how to optimize what I have.

One of the resources that the parts shop called and asked what a good minimum distance between top of stack and lid said that 2" was his min distance and 6" was even better(I think the latter was partially in jest). And based on what buggies and baja's can get away with.

[Alstrup]

In a perfect world we like to have the venturi diameter as space between the stack and the filter top. In real life that is rarely happening, because when comes down to it the intake length has more influence on the power than the perfect free space over the stack. The reason is that most stacks are, at least to some extend, shaped for good air pick up around the outer perifer. That extra mouth width can make up for a good deal of free height.. Of course the more power the engine makes and thereby the more air it needs, the more important the free space gets. also, the higher rpm the more important the free space gets.
If you have say a 2275 with 44 IDF´s that has 36 mm venturies, 58 mm stacks and 27 mm free space over the stacks, it will still pull 170 - 175 hp with out problems. But you might notice that it may have a little more power over the curve if you remove the filter top.
If that same engine is on the edge, meaning 38 mm venturies, hot cam´n compression etc etc, you will definitely get an advantage by having the venturi diameter as free space over the stacks.

The 6" filters that you see around is not necessary as such. The advantage is that on baja´s etc you slow down the incoming air through the filter so that the filter has a higher chance of parting sand and air. also, some baja´s runs with some very long stacks to try improve torque. Then they of course need high filters too. If we look at it from a flow perspective, one 6" filter will flow enough for at least 210 hp and there is usually 2 filters on a dual carbed engine

Hope this makes sense to you.

T

[Alstrup]

Woops!

[ps2375]

Mine is only a 2087, but does have 36 vents and I would love for it to make 170-175hp, but I'm guessing it is far below that. So, from what you have said, I most likely won't see any gains from adding free space over the stacks, but I think I will proceed with my plan as it won't hurt anything.

[mark tucker]

top shape can give good results too not just adding more space but using some direction of the incoming charge.

[modok]

As far as airflow is concerned 1" is probably ok
As far as the carburetor signal is concerned, 1.5 min
For containing reversion fog, 2" is needed

So why do they make tall stacks at all?
The fog hits the lid and goes out the sides of the filter, getting it wet and wasting fuel too. This will give you some strange AFR results.

Gauze filters will stand this but if you want to have air filters that clean the dust out of the air They won't stand it, then you will need 2"+ clearance.

[vince1]

Switched from K&N E3341 to HA0800 and the engine fell better in upper range. Small A/F ratio change too.

E3341 are a little thinner than what we find in empi and CB packages.

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[ps2375]

Looks like there is nothing to lose and can only gain, if there will be changes.

[theDrew]

[ps2375]

[ps2375]

Here's where I'm starting from, about 1-1.25" from top of stack to the lid.

Here's how it'll happen.

I took some extra tops and bottoms I had, tacked them together and had a friend weld the seam.

Then I cut and ground on them till they looked like this:

So that my new 1.75" filters fit like so:

To allow my existing filter to sit as such:

After powder coating and install, I should have close to 3" from top of stack to the lid.

[mark tucker]

I wood add some small tangs so the filter's cant warp inward any in the center portions(slide in the housings inward) I do like your idea. I wood add a inverted conewith flair where it meets/connects to the tops.(welded to be one peice) to help the incoming charge be directed for better flow.... of corse if you had a flow bench you could test all kinda shapes to find what works best than....have them injection molded or cast & sell the crap out of them!!!

[ps2375]

[Frankysfree]

Is there a big disadvantage to only running filters without velocity stacks? When i got mine it had 40 IDF's with no stacks, only filters. I understand the reason to run the stacks just wondering if it will lose a significant amount of power or tq by not running them or will it be slight. Are there any dyno sheets to show the power difference?
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[ps2375]

I haven't seen any dyno comparisons, but the stack or any stack will aid the directional control of the air going into the carb, reducing the turbulence in the carb throat and improving the "vacuum signal" at the venturies and make tuning more consistent. At least that is what I have found in the reading I have been able to find in various forums and articles. But, it is all on the internet, so who knows. There is mention of some tests on kads w/ and w/o stacks in various threads, and w/ stacks was better.

[tattooed_pariah]

[dsrtfox]

Maybe you could shorten the stacks ?

[ps2375]

With my current config, the motor runs well and I don't notice any problems, I just know that the stand-off fog washed the plasti-dip off the undersides of the lids. From what I gather, the extra room won't fix a tuning issue, but might help with consistency of jetting and could effect the tune a little.

[cliveawn]

Interesting thread,do running stacks reduce induction roar?
My motor roars a bit and it does get annoying on long trips.
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[ps2375]