[rackops]

From my seat-of-the-pants experience (e.g. not technically verified)...in my 1931 Victoria, I drove it with the following:

Model B engine with Model B carb (Model B intake)
Model B engine with Model A carb (Model A intake)
Model A Burtz Block with Model A carb (Model A intake)

Of the carburetors, I built and tested over a dozen from both types (I rebuilt and then sold them on eBay). All of these were Zenith/Holley carburetors, including single and double venturi.

To be honest...there wasn't a huge difference. The Burtz Block engine was different, and I was quite pleased, but as far as how the carburetor affected performance...I didn't see a significant difference. There was never an "OMG! I need to tell everyone that this carburetor is the BEST THING EVER!" event. Once I got both the Model A and Model B carburetors tuned in, they ran well and were dependable. But...nothing incredible happened as far as operational differences.

I will caveat this by saying that I live near the coast and most of the roads here are flat...so I rarely drove up or down hills (save for a local bridge). I am certain hill driving would be different...but I don't have any to test.

I've never driven a Model A with a downdraft, but I have a feeling it would be very different, and quite possibly be the difference in performance people are looking to achieve.