[Formulajones]

Originally Posted by Steve C.

Regarding the Holley carburetors and a similar situation Jim Hand did for the Q-Jet carb and the mention of the Stubstack. Testing has shown that the contoured venturi inlet on the Holley 'HP' series carburetors offers balanced airflow for increased horsepower over a carburetor design with a choke tower. The Stubstack with its smooth contour cleans up the flow and the engine responds to that.

https://www.knfilters.com/racing/stubstacks.htm


A fwiw, it's nothing new. One of the all time best custom carburetor builders Brad Urban did a similar thing many years ago. On his high performance Holley carburetors for maximum airflow the choke tower was machined off and he did a CNC radiused air entry.


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Yep I did that back in the 80's to a 3310, milled the choke horn and spent a ton of time with a flapper wheel smoothing the contours of the bore entry, and even used a little epoxy in small areas.

That was a whole bunch of work for not much gain at all, lol. I still have that main body. It went on the shelf when affordable main bodies that looked much prettier started hitting the market.

I never could find any gains with a stub stack. Not sure why, but after all that work modifying that 3310 with little benefit I wasn't the least bit interested in making a stub stack look-a-like for a Q-jet or even modifying a Q-jet air horn for that matter.

What is interesting though is that home made funnel Jim used on the bottom of the lid. Some of the OEM lids found on Chevrolets that have a much deeper recess for the wing nut kind of mimic this and I can see how that may be beneficial.
Some of the aftermarket aluminum dome lids you see used a lot on sprint modifieds also have this feature.

I however have no room for that mod on my Formula. With it's factory ram air setup, the bottom of the lid at the wing nut is only 1/4" from the choke horn, and I have no room at all to move the lid higher.