This is REAL technical information.    People tend to glaze up.when I start talking like this.
Appreciate seeing an intelligent man share invaluable information.

Scott, you are doing such amazing work with these videos. The 472 / 500s are not talked about nearly enough. Thank you for being such a solid source of information on these.

Keep it up!
-Luis

The old carb formula is based on steady state flow, which an engine doesn’t experience!

Very nice presentation. I had a 4150 on my Mustang with a 302 and fairly hot cam. A few idle tweaks and bowl fuel level tweaks, and it was a reliable runner. The Vacuum secondaries was a key. Tune the vac side to what the engine demands. Several spring changes, and we're happy.
You clearly point out the value of the vacuum level.

Now the next chapter would be: The difference between a square bore and a spread bore :)

You need to put a microphone on your person near your collar. It sounds like an echo on my end.

Small point to make.

Fuel is pushed into the venturi as the pressure in the fuel bowl is nearer to atmospheric than in the venturi.

Anything called a vacumn is really only pressure that is less the local atmosperic pressure.  Fluids, like gasoline and air, move from high to low pressures

An intake vacumn is just a lower pressure than the location at which you are measuring it, and is relative to the pressure at that point.

28" of water column is equal to a pressure difference of 1 psi.

I removed the 750 carburetor from my 427 W in my hot rod and installed a Holley 350 street avenger. The result was great throttle response, better gas milage, 14.2 AFR better all around drivability. I am just driving on the street and don't need all the power the 427 W has to offer. The car is so light and the engine is so big that I never used all four barrels of the 750 anyway. The 350 works just fine in my application.

most auto manufacturers uses an undersized carb for an obvious reason : bigger a carb is for a given engine, more sensitive it is to atmospheric changes so when you go for an oversized carb, you buy a passport for continuous tuning sessions.

Hreat video! So many people on YT know nothing but the wrong formula only with no info behind it!

Very informative Scott. Thanks for your comments on my channel. AG

Thnx for this video Scott .  How important is venturii sizing to the throttle bores of the carb ?
I've got a 750 carb w 1.40" dia. venturii and 1 & 11/16 " throttle bores . Going to use 12 - hole annular boosters instead of downleg for my 437 c.i. 8.50 :1 poncho motor w sgl turbo . No more than 12 # boost and maybe 5500 rpm w torker 2 intake . Should this combo be ok for street / road course work ?

Kind of in the weeds technical, but necessary to know, if you want to get in the ball park with combination. I run very mild sbc stuff, and a small carb is much more pleasurable than a too big barb. I street cruise and foot brake race my mild sbc, but it is still a street combination, not an all out race combo.

Stan Weiss

How does this apply when you have individual  carbs with a butterfly for each port like a pair of Weber DCOE carbs on a 4 cylinder?

My promaxx heads at 500 lift are 278 cfm times 3.38 is 936, so I want a 950 cfm carb? My cam is 485 lift my 650 and 750 carbs are sluggish and bog all thru the range of rpms

Use a mike,  use a mike,  use a mike !!!!!

Thank for your presentation. However I don't understand how converting from 28 to 20.4 results in 3.38. Seems to me it should be (20.4*4)/28 which is 2.91. I'm asking because I want to calculate the carb size for a 6 cylinder engine which I think is 3 times (runner flow rate) times the adjustment factor.

What is the best way to flow a Q-Jet?

Can you explain air bleeds?
I understand a smaller air bleed gives you more fuel at high vacuum and at low vacuum not so much. But I am unclear about it.. It isn’t the same as changing jet sizes?  🤔
Also part throttle discussion- you know where we are 99% of the time.  On the street.