velocity stack

guys what is the function of the velocity stacks in 44 IDF dual weber carbs? should one use them alone or with the air filters??
what size should one choose if necessary?

the increase air flow. i use them on my 44 IDF's with K&N air cleaners installed. IIRC - the filters are 3.5" tall.

Used mainly for racing - they suck in grit big time which decreases engine life so wouldn't use on the street.

Yes, they do increase dirt in the carb's if you don't use air cleaners but, I assume you're using air cleaners so that threat is diminished.

I highly recommend them for Webers or Dellorto's. They smooth out the air flow to the venturi's and provide an even amount of air to enter the carb's.

Another benefit is they allow a place for your air balancing tool to rest while your syncronizing your carbs.

Seems that they're mainly for looks on a carb engine. They might have been needed on the old fuel injected drag engines, though.

http://en.wikipedia.org/wiki/Velocity_stack


FP

According to the Weber website, you MUST maintain a minimum of 1.5 inches of air between the top of a velocity stack and the bottom of your air cleaner or you gain nothing, and maybe even lose a bit. Here is a shot of the air cleaner risers I added after putting velocity stacks on my 44 Webers. Risers are little over 1.5 inches. Had to cut out the decklid inner panel on right side to achieve 1/8 inch clearance between the top of the air cleaner to inside of decklid. Tight fit but it works!

Hmmm... Wanna make a few sets for sale?

David, nice bit of work but did you know that K & N makes taller air cleaner elements. All that's necessary to install them is some threaded rod to secure the air cleaner top.

Velocity stacks are made in various heights. They assist in obtaining low end torque, mid range torque or high speed performance. These characteristics are controlled by the height of the stacks. The choice is yours based on the performance improvement desired.

Larry, I checked out every K & N that would reasonable fit on my speedster. Too short and too tall were the only sizes I had to choose from. So I made my own risers. As noted earlier, by maintaining the "Weber required" 1.5 inches of clearance above the top of the stack to the underside of the air cleaner lid, I still had to cut the decklid inner panel out. I even had to file down the outside edge of the right side aluminum air cleaner cap to assure clearance to the deck lid outer panel. Really tight fit, but it all works well. No clearance issues to deck lid on the left side. I am very happy.

Kept wishing I had access to a milling machine or aluminum castings in order to really do the risers justice. Not finding any such machinery in my garage, i just made it up from bits of alngle, sheet stock and rivets.

Larry,

I was searching too. I may have a bit more room than David, so if you have a part number handy, would you post it. Thanks.

Unfortunately, I don't have a part number and,, it all depends on what original size filters you have. I've had great luck calling K & N and speaking to one of their tech guys, giving them dimensions and getting alternative filter numbers.

Here's their web site:

http://www.knfilters.com/

Webers and Dells that do not use a velocity stack are very difficult to properly tune as the veocity of the air is critical to the atomization process.

I maintain 36mm at minimum from the top of the velocity stack to the bottom of the air filter.

I dug thru the K&N site last week (5-13) when Larry originally posted and bookmarked this:
http://www.knfilters.com/Racing/customcarb.htm
Top section covers most VW applications; bottom section, 1/2-way down the web-page, is all Weber. Also, app. notes at bottom. If you're still unsure about your particular fit, call K&N tech and see if they can provide you with the dimension(s) in question.
Add-here's a Weber link I noticed in my saved favorites for what it's worth (just sharing info):
http://www.webercarbsdirect.com/Free_Downloads_Weber_Carburetor_Schematics_s/76.htm

Jake's got it.

I wrote a post a long time ago on here detailing the use of velocity stacks. All of the info came from Bob Tomlinson's Dellorto Tech Book. Here you go: https://www.speedsterowners.com/forum/readmsg.asp?t=3177

gn