As to the density, it’s the mass of air/fuel an engine sees and needs more of to increase power. Because an engine has volume and air/fuel mass is being induced then you have a density of air/fuel (density = mass/volume). I’ll let a Mike Urich & Bill Fisher quote from Holley Carburetors & Manifolds help explain:
”Many people believe the throttle controls the volumeof fuel/air mixture being pumped into an engine. This is not the case. Piston displacement never changes, so the volume of air pulled into the engineis constant for any given speed. The throttle controls the density or mass flow of the air pumped into the engine by the action of the pistons: Least density of charge is available at idle, highest density at wide-open throttle. A dense charge has more air mass, hence higher compression and burning pressures can be developed for higher power out-put. Thus, the throttle controls engine speed and power output by varying the charge density supplied to the engine.”
Mr Campbell was saying that ultimately the air-valve style carburetors cannot supply as much air/fuel mass as the plain tube carburetor due to the air valve design/function. That’s how I heard it anyway. I wouldn’t think he was talking of 11 sec quarter mile level or of those test you refer to Geoff, but of a higher hp level.
I took all of what he was talking about from a high performance perspective. So when it comes to drilling of the main wells etc I wouldn’t contemplate it if my tuning goals were efficiency and emissions as it would be pointless. But looking for a performance advantage it may be worth the trial to get some old blocks and do a before and after test. What he was referring to is that due to a liquids propensity to adhere to a solid (fuel to well wall) it is too hard to get the smaller volume of fuel of the standard diameter main well moving quickly so enlarging the well allows more fuel away from the wall to get moving quicker. Remember he said a main jet change would be in order to balance pressure differentials. Larew speaks of this wall adherence in Carburetors & Carburetion:
”The surface tension of gasoline and the adhesion of gasoline to the surface of a nozzle cause the gasoline to tend to stay in the nozzle”
And
”Assume also that the air bleed orifice is closed. Then the head tending to cause a fuel flow through the nozzle may be such that the fuel flows in a series of large drops from the nozzle because of the surface tension and fuel-to-nozzle adhesion above, or perhaps does not flow even though it is above the bottom of the nozzle opening.”
So I took the reasoning by Mr Campbell for opening up the main well to .180” to improve fuel flow between lowest active emulsion bleed and main jet. Opening angle channel and booster leg to .166” may perform a similar function or required to support extra fuel.
Geoff, check out the below link. Under ‘How Edelbrock Created its Nearest Competitor’ it’s mentioned that Edelbrock were working with Carter as early as ‘73/‘74 with the AFB. There was reason for them to start favoring the AFB.
https://www.motortrend.com/news/hrdp-13 ... edelbrock/Statistics: Posted by Right hand drive — Mon Mar 28, 2022 10:09 am
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