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Old 11-18-2017, 06:36 PM
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Tom Vaught Tom Vaught is offline
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When I first began to learn about Carburetors, Holley Carburetors, from the people who actually designed them in Warren Michigan I was fortunate to see in operation how the carbs were tested for Air Flow and Fuel flow (using Stoddard Solvent). Even though Holley had a 3000+ cfm Air Flow Bench (first built to flow the massive Carburetors used on the Supercharged Aircraft engines built during World War II), Holley preferred to use 8 Flow Benchs that were hooked up to a 8 sliding drums with a precise Constant Volume, Constant Pressure, Constant Temperature design.

The Technician raised the known volume drums by filling them with temperature controlled air until they were fully filled to a precise pressure.

At that point, the carburetor was already installed in a enclosed air chamber and had fuel (stoddards solvent) flowing into the carb fuel bowls. The throttle blades had been set by the Technician for the .020" window in the transfer slot and the choke was fully open.

So then the Technician released the upper drum and for 1 minute it dropped slowly downward and then he read the idle air flow in one minute.

Typically, for most Holley carbs, it was in the 16 to 19 cfm range on the Primary Blades. The Secondary Blades were barely cracked (not touching the walls of the carb base plate). Usually this .020" Throttle Blade setting also matched up with approximately 1-1/2 turns of the Primary Throttle Adjustment Screw.

So the drum was raised several times and the test repeated then the Technician moved on the the next checking point on his test sheet.

After multiple checks, at different Throttle Blade settings, the Technician would have data which could be plotted on an 'airflow vs fuel flow' graph. They did this work for both initial designs for new carbs and for verifying carb production build quality control. Samples of each carb series produced in that month were sent to Warren Michigan for verification of the flow numbers. Holley also had smaller flow stands at the plants for spot checks during production. I observed hundreds of tests but never actually performed a test. That was the Technician's job.

At the end of the day the Carb specs for a given carb model would be checked against a Master Build Carb Sheet with the flow numbers of the Master Carb vs the 'Tested Carb'. Master Carbs were considered to be Perfect Carbs in all circuits of the carb design.

So when you bought a 3310-2 Holley Carb or a 4779-2 Holley Double Pumper Carb, or a 4412-2 Holley 2 BBL you knew exactly what you were getting. In many cases you did not need a whole box of Holley carb jets to dial the thing in for your application because 4 set sizes larger or smaller than what was installed in the carb (stock) typically covered all installations.

All that being said, Holley also had a Test Track to test the carbs on given production vehicles.

They had a Engineering Building with Hundreds of Engineers working in the buildings. They had Engine Dynometers and Chassis Dynomometers as well as two Emissions and F.E. Chassis Dynometers.

Then you had the Calibration Engineers who worked with the OEM people (In those days: Ford, GM and Chrysler) doing constant test drives on vehicles (with the OEM Engineer) using Horiba Air/Fuel Measurement tools costing thousands of dollars (at the time). I still have one of those old test set-ups.

From the web: "HORIBA Automotive Test Systems is a leading supplier in the fields of engine test systems, driveline test systems, brake test systems, wind tunnel balances and emissions test systems. More than just the world's leading supplier of emissions testing systems, HORIBA ATS is able to provide total solutions to its customers, with full turnkey capability."

So everyone who wishes to make their Holley Carburetor better vs the stock piece out of the box (old OEM calibrations) better be on their game.

Have a great weekend!

Tom V.

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"Engineers do stuff for reasons" Tom Vaught

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Last edited by Tom Vaught; 11-18-2017 at 06:42 PM.