Velocity stacks

Is anyone out there running Webers with velocity stacks INSIDE the air cleaners? I was recently advised by an engine builder to add them if at all possible. In my case, I have the 2 1/4 inch high stacks. The air cleaner is only about 2 1/2 high, and a taller air cleaner will not fit under the deck lid, so this won't work well with what I have. But I was wondering about the value of swapping my stacks for some shorter ones? Anyone got some real life experience with stacks?

While synching the carbs recently, I briefly added the long stacks and to my surprise, the RPM even at fast idle, increased noticeable.

Good thread! Like to hear the thoughts on this issue! Always looking for more umph.

Bruce

my vote===great addition, straightens airflow thru venturi
note----no official, personal testing was performed while
coming to this conclusion. they look cool too!

I got 'em tucked in the air cleaners (short stacks) on my current 40 Webbers and there was a marginal seat of the pants feel on acceleration. Mostly they sounded more cooler!
Aircleaners are important because it keeps the turkeys from getting sucked in... I just read that somewhere, or maybe somebody was just pissing in my ear? Seemed like a lot of that goin' 'round today.

Gee, I'm surprised that Webbers don't (apparently) have velocity stacks standard. I've got a pair of Dellorto 40's that had stacks installed when I bought them new.

OK, from the Dellorto Tech Book:

1. The use of some form of velocity stack (VS) is recommended over no stacks at all.

2. The purpose of the stack is to straighten and direct the flow of air into the throat of the carb.

3. Stacks should be matched to your air cleaners and should have a minimum of 34mm clearance between the bell of the VS and the under side of the air filter lid to allow proper air flow into the stack's bell.

4. The rolled bell entry helps to reduce turbulence and to contain fuel stand-off (a cloud of vapor surrounding the top of the carb or velocity stacks and caused by valve overlap and sharing an intake manifold runner with two intake valves - not common to dual-port Air Cooled VW's due to one intake valve per carb bore).

5. Using taller VS's showed marked improvement in mid-range torque and upper end power under certain conditions. "For example, you won't see any improvement when you install tall (6") stacks on a set of 36mm carbs running on a 1641cc engine. Add the same 6 inch stacks to a pair of 40mm carbs running on a heavy breathing 1915cc engine and you'll see a noticeable increase in performance."

6. Taller stacks will effect the final choice of main jets due to the additional ram effect of the increased air flow. Typically, moving up one or two jet sizes will better match the fuel to the increased air flow.

7. Running open stacks can be detrimental to your engine's life due to entry of dirt and dust causing subsequent engine wear.

Just for the heck of it, I went out in the garage and checked, and my stacks are around 3" tall, and I have over 1 1/2" between the VS bells and the cleaner lid. Looks like a trade-off between all-out performance of taller stacks on a drag car, and fitting them into a daily driver with sensibly sized air cleaners.

Hope this helps (or encourages more discussion)

Gordon

Just recently bought a new set of Weber 44s. Came with velocity stacks...but I have the taller cleaners, and clearance is no problem on my IM.
Ron

Most dual Weber IDF kits come with velocity stacks; older IDF's had semi-stacks cast as part of the carb cover. Weber and Dellorto both state that the top of the stack should be at least 34mm from the base of the air cleaner's top cover for best performance. The steel Weber stacks are smaller than 48mm at the bottom while the Dellorto cast aluminum stacks are 48 mm, which makes a difference if you run 48 IDF's.

The Dellorto stacks are also slightly shorter than the Webers, though you could cut the Webers (or Dels) down if desired.

My old car (Karl Maklin's 2,110) is running 48 IDF's with CB linkage and K&N filters with stock Weber stacks that have a bit less than the 34mm clearance but it runs fine.

Ahh you type one guys. Did I forgot to mention in my original inguiry that my Webers sit atop a type 4? The clearance from top of original stacks to top of air cleaner is less than 1/4 inch (that's no good). And the clearance from top of air cleaner to deck lid is less than one inch (that's no good either). So it is short stacks inside the air cleaner or nothing at all, which is where I am now.

Is any body actually running short (1 1/2 inch) atacks?