I have acquired a Holley mechanical secondary double pumper carb that has had the air horn milled off eliminating the identifying numbers. I was told by the seller that it was an 850 but I have since determined that it cannot be an 850 due to the smaller 1 9/16" throttle blades all the way around. The blades are numbers 172 and 173. Other than the blades I have numbers p 46 on the driver side main body and r 24 on the passenger side main body. The metering blocks have numbers 8543 on the primary and 6501 on the secondary. I have a power valve only on the primary metering block. Anyone with knowledge of Holley carbs please post what you know. I do appreciate it!

Measure the ID of the venturi.

If it truly has 1-9/16" throttle bores(not 1-11/16"), and is a double pumper...... It's a 600.
As I recall, "most"(if not all) 600dp's have brass secondary throttle blades...... Although I haven't had one in my hands in several years.

If is has 1 11/16" throttle bores, then you need to know the Venturi diameter...... Unless you've been messing with them forever, in which case you can tell just by seeing the Venturi shape/size/booster config and just "know".

if you google holley 172 and 173 blades i think you will find they are actually 1-11/16" blades, i'm going by memory so i could be wrong.

I think you're right.

The quick-look ID for the non-race type 1-11/16 throttle bore carbs:

650-bar type boosters, pri/sec Venturi diff size

700-bar type boosters with flared bottom, pri/sec Venturi diff size, 50cc rear pump

750-downleg boosters, all Venturi same size

800-downleg boosters, pri/sec Venturi diff size, 50cc rear pump

I think you might be right too. Today I had a friend with Holley knowledge take a look at it. He says removing the rear power valve or replacing rear metering block is an old drag racers trick to allow use of even bigger secondary jets or something like that. He also said he believes the carb is an 800 cfm. ??? I got it installed and dialed in and my built 440 absolutely loves it!

Measure the venturi. Could be an 830 as well.

I have a venier caliper but its jaws are too short. What do you use to get an accurate measurement?

spread a paperclip till it just touches the walls, then pull it out and measure it with caliper.

Or a snap gauge. Those can be had pretty cheap in a complete set.

THIS.............Do it all of the time.........

Dam Dom, I'll gonna figure out your birthdate and send you a set of snap gauges for all the help you've given me!!!!!!!

I see how that looks............lol I meant I use inside calipers then a tape measure which gets ya close...........NOT a paperclip...........

The carb in question has 1 3/8" venturies front and rear and 1 11/16" throttle bore diameters front and rear. Based on these measurements the carb appears to be 750 cfm. Thanks to you all!