It's all upside with velocity stacks, especially with larger (1915 and larger) engines.  The system has also been called "Ram Tuning" or "Ram Induction" over the years, too.

They help to straighten and accelerate the airflow through the carburetor and are primarily used to increase mid-range torque and upper end horsepower (sometimes dramatically) depending on the rest of the engine/carburetor configuration.  The larger the engine and the taller the stacks (within reason) the more HP increase you'll see.

There are several different stacks available for Dells, either from CB Performance or Aircooled.net   The trade-offs to be considered are: (1.) how much clearance do you have between the inside of the engine compartment and the top of the proposed air cleaner and (2.) how tall a stack can you fit inside of that air cleaner, keeping in mind that you need at least 36mm (1-3/8") space between the top of the stack bell and the inside of the air cleaner top for them to breathe.

Other than that, the taller the better on the stacks because taller means more torque and HP, but you're gonna be restricted by the available space in the compartment for cleaner clearance.

The next question is usually "Yeah, but do I really need a big Air Cleaner?  I could run taller stacks without it."

That's true, but you're risking your engine sucking in some foreign matter which might destroy it.  Better to at least have a small filter on top of each stack than nothing at all and the best thing is a dual-throat filter running a K&N filter element.

If you go from no stacks to 3" or taller (especially taller than that), you may need to re-jet the Mains to take full advantage of the added air being rammed through the throats to achieve max horsepower - maybe one or two sizes bigger should do and they're right on top of the Dells and easy to change.  I wouldn't expect a need to change the idle jets - at most one size up.  CB has a YUGE! selection of Dell jets.  They also have the stacks - Dell stacks (any size carb) are the same as Weber IDF stacks.  You may need to mess with the base mounting flanges to get them to clear the filter elements on K&N filters, but that's minor. 

BTW: The Tomlinson Dellorto and Weber Tuning Bools have a whole discussion about velocity stacks.  I've also heard them called "Zoomie Tubes"  but those get confused with header tubes, too (it's a weird hobby, motorsports).

Interesting. Thanks! I am running dual Dell 42's  on a 2110 stroker with a mild cam.  I was considering at least 3 1/2" stacks, CB Perf. #6379,  and the CB Perf. #6373 individual filters as a potential option.

I have the car on jackstands now for front disc brake swap and adjustable spring plate installation, so, since it's already down for awhile as I've got a list of other non car related projects and our weather currently sucks, I might as well toy with some other stuff as well.

The stacks are very easy to install - You'll probably still need the bottom plate of the air cleaner if you're also using the CB Perf. hex bar linkage, but you remove four nuts, pop on the stacks, re-install the washers and nuts and then affix the air cleaner elements to the tops of the stacks (they also sell covers for the stack tops).  That's it.

I can't remember how tall mine are.  If I get out there later I'll measure them and report back.

Panhandle Bob posted:

I don't know where I got the idea that my Dells were 42 mm. They are 40's duh!

I knew it was a brain fart, Bob.

The biggest stacks that are going to fit under the air-cleaners are 1-7/8" high. I thought they came with the CB kits, but I don't see them listed in the parts breakdown. CB has them for $7 each.

Lemme' check my stash-- I think I've got an extra set I can send you.

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