Re: Corvette SAE paper collection
The Rochester FI system is actually fairly straightforward in its operation, but it depends on a lot of precision mechanical parts to function properly, so wear and hack mechanics can take a toll.
BTW, the paper states that the total loss across the air meter (early version) is 6" H20 at 24 lbs/min air flow. At standard sea level air density (.0785 lb/cu ft) that's 305 CFM.
Using the square root relationship of air flow to depression and converting inches of water of inches of mercury (13.6" H20 = 1" Hg.) flow at 1.5" HG depression, which is the industry standard depression for measuring four-barrel carburetors, is 562 CFM.
The late air meters that don't have a closed end cone (not all the air flowed through the annular venturi) is greater so the generally accepted 600-650 CFM is probably close, and they can be "massaged" to flow 700-750 CFM.
All air meters have a 3" throttle bore and a large diameter butterfly shaft - 0.5" - was required due to a load of up to 75 pounds on the shaft at high manifold vacuum. The thick butterfly and shaft cause as much if not more loss than the annular venturi.
The only issue I take with the paper is that the system doesn't really meter fuel on the basis of mass air flow. Like a carburetor, it meters on the basis of volume flow, so A/F variation occurs due to air density variation, such as richening as a car is driven from low to high altitude.
Duke
The Rochester FI system is actually fairly straightforward in its operation, but it depends on a lot of precision mechanical parts to function properly, so wear and hack mechanics can take a toll.
BTW, the paper states that the total loss across the air meter (early version) is 6" H20 at 24 lbs/min air flow. At standard sea level air density (.0785 lb/cu ft) that's 305 CFM.
Using the square root relationship of air flow to depression and converting inches of water of inches of mercury (13.6" H20 = 1" Hg.) flow at 1.5" HG depression, which is the industry standard depression for measuring four-barrel carburetors, is 562 CFM.
The late air meters that don't have a closed end cone (not all the air flowed through the annular venturi) is greater so the generally accepted 600-650 CFM is probably close, and they can be "massaged" to flow 700-750 CFM.
All air meters have a 3" throttle bore and a large diameter butterfly shaft - 0.5" - was required due to a load of up to 75 pounds on the shaft at high manifold vacuum. The thick butterfly and shaft cause as much if not more loss than the annular venturi.
The only issue I take with the paper is that the system doesn't really meter fuel on the basis of mass air flow. Like a carburetor, it meters on the basis of volume flow, so A/F variation occurs due to air density variation, such as richening as a car is driven from low to high altitude.
Duke
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