I'm considering making a fixture for doing airflow testing of carburetors on my lil' SuperFlow 110. However, I'm wondering if there's really valid data to be gained from this, especially since most of the testing would be restricted to one venturi at a time, or two at a time at most.

I know that wet flow #s can't really be calculated from dry flow since different booster designs (e.g. downleg vs. annular) have a varying effect / impact on the wet flow characteristics.

Is there still a benefit to dry-flow comparisons of different carbs and / or checking booster draw rates for consistency across all the venturi? Anything else that can be gleaned from this method of testing?

If not, I'll save the time & $$$ and skip on the fixture.

I use to have my carbs. flow tested by a shop that had two Superflow benches, 110 and a 600. Origianlly they would test the carbs. on the 110 at 5 inches, one venturi at a time. That machine broke so they strated flowing them on the 600 through all venturis at once. I don't remember having the same carb. tested on both but I did find out on the 600 bench that my new,to me, at that time, Holley 950 HP did not flow 950 CFM, more like 880 CFM, my stock Holley 4781-2 850 DP flowed like 910 and a a freinds BG 750 stage three heavily modified 750 flowed 920 CFM I guess the message is they(benches) are both measuring devices, what you do with the results is important to those wanting them Inforamtion can be dangerous, lack of information can be more dangerous

There are things you can find, like a booster maybe a little crooked causing flow loss. I know some guys will flow 1 venturi with a manometer hooked to the main flow well with a little tube to see how each booster is working compared to the others. It's also a nice way to do a little bit of deburring in the venturi and bores and making sure they all a close to one another in flow.

I spent far too much time doing this type of testing on the annular booster setup I made for AVS carbs.

http://www.nzmoparforum.co.nz/index.php?topic=7933.0

it did work but I can sum it all up for you in about 2 lines

Carb flow & jet signal are a balancing act & more often than not if you change one you will compromise the other.
eg, tidying up your booster leg or venturi for better flow lowers the signal to the jet while increasing the signal to the jet with annular or skirted boosters will decrease the flow of the carb.

I already have a separate manometer that I've used for some limited port velocity testing, so I'm good there.

I haven't decided exactly what configuration I'm going to build; I have a couple of different approaches in mind, neither of which are that complex. Regardless, the total cost to make something functional should be far less $$$ than what the commercially available carb flow-test fixtures would cost to purchase.

Also, I have an idea or two from some stuff I've read that makes me think using a fixture that bolts directly to the deck of the flow bench isn't the best way to test. Instead, locating the fixture on top of a cylinder head adapter of adequate bore size (looks like my 4.375" bore adapter is about right) to give the carb something more akin to an intake manifold plenum to discharge into before dropping into the flow bench's "black hole" is supposed to be better for pressure recovery characteristics.

Let me throw you a curve on how some of the NHRA class racers have flow tested there heads, intake manifolds and carbs. Bolt the head to the bench, bolt the intake to the the head and cover most of the other intake ports( figure out which other intake valves are open and how much there opened compared to the port your flowing off of for your tests and restrict that port window that much ) and then bolt the carb. on the intake. Do more than one port on both sides and go from there

FWIW, I have started to piece together a carb flow-test fixture. "440 Jim" has fabbed a part for it that should pretty much complete the assembly once it arrives.

I have a few different 4150-type carbs to try and am hoping the #s make some sense, despite the tests being run on a low-capacity bench. My baseline carb is a basic 4781 Holley 850 DP w/o a choke plate; I'll test some other stuff after seeing what sort of #s and consistency I get trying out the 850.

Fixture completed... now just need some time to throw some carbs on the bench and see what they do.

Brad,
i look forward to the results.especially as i may step up my carb when the new heads,for me, go on my 440

Tex

Post some pictures of the complete setup.

Although I have taken some pics, I haven't downloaded them from the digi-cam, yet. In the mean time, here's some data from what I've tested:

Carb ------------------------------------------------------------ (TM) --Dry Flow -- Calc'd Wet

Holley 3310-2 with choke ----------------------------------- (A) ----- 796.6 ----- 732.9
Holley 3310-2 with choke ----------------------------------- (B) ----- 811.6 ----- 746.7

Quick Fuel “950” 1.45 v body on Demon RS baseplate -(C) ----- 964.4 ----- 887.2
Quick Fuel “950” 1.45 v body on Demon RS baseplate -(D) ----- 963.0 ----- 886.0

BG (Gold Claw / Demon RS) 1.425 venturi sleeve ------ (C) ----- 960.4 ----- 883.6
BG (Gold Claw / Demon RS) 1.425 venturi sleeve ------ (D) ----- 958.1 ----- 881.5

BG (Gold Claw / Demon RS) 1.500 venturi sleeve ------ (C) ----- 982.9 ----- 904.3
BG (Gold Claw / Demon RS) 1.500 venturi sleeve ------ (D) ---- 1001.3 ----- 921.2

BG (Gold Claw / Demon RS) 1.562 venturi sleeve ------ (C) ----- 994.1 ----- 914.6
BG (Gold Claw / Demon RS) 1.562 venturi sleeve ------ (D) ---- 1012.0 ----- 931.0


Test Methods (TM):
1. Method “A” means this test was of a single primary bore AND then a single secondary bore with the results being added together and the sum multiplied x 2 for a Total Dry Flow #
2. Method “B” means this test was of both primary bores AND then both secondary bores with the results being added together for a Total Dry Flow #
3. Method “C” means this test was of a single bore (either primary OR secondary since the venturi have symmetrical entries) and multiplied the result x 4 for a Total Dry Flow #
4. Method “D” means this test was of either both primary OR both secondary bores (all venturi have symmetrical entries) and multiplied the result x 2 for a Total Dry Flow #

Other comments:
A. Not sure about the discrepancy between why the “A” and “B” results for the Holley 3310-2 varied as much as they did. The primary bore(s) results were virtually identical with both methods; all the variation was experienced during the tests of the secondary bores. I've read where some carbs when testing multiple venturi at the same time show better results than trying to combine the results of the individual venturi... this seems to be an example of that.

B. Test Methods “B” and “D” required lowering the test pressure significantly due to the small capacity of my SF-110. However, trying to test the two highest-flowing combinations using Method “D” required dropping the test pressure so low that I believe that lower pressure introduced a level of inaccuracy not experienced with the other tests.

C. The Calc'd Wet Flow results are simply the Total Dry Flow #s x .92 to subtract some flow for a theoretical 12.5:1 A/F ratio. I have no idea how close this comes to the reality of actually wet-flowing a carb, but it's something of an industry standard. I also suspect that – if it's an "in the ballpark" correction value – that .92 adjustment probably doesn't work for something like an annular booster which has different atomization characteristics that “use” more of the available airflow.

D. The Total Dry Flow #s posted include a 2% temperature correction (reduction) factor on my flow bench for intake results. If you want the “raw” Dry Flow #s, take my Total Dry Flow # and divide by .98 to get the pre-correction #. Example: 982.9 + .98 = 1003.0

E. The Demon RS 1.75” baseplate used for testing the Quick Fuel main body and the various BG (Gold Claw / Demon RS) venturi combinations has slabbed throttle shafts which are supposed to be worth 20 +/- cfm over standard “round” throttle shafts used by most Holley carbs, Proform carbs, Mighty Demon, etc. Quick Fuel uses a similar slabbed throttle shaft with their Q-Series and Race Q carbs.

F. I have no idea how BG came up w/ the wet flow #s they published when the Gold / Silver Claws came out (see the #s I listed in an earlier post on this thread). I know my test equipment is freakin' primitive, and maybe not having a "big gun" flow bench is skewing the peak #s lower for the larger venturi combinations, but...

Great post.

As I read it,
Method A & C blocked off 3 of 4 venturii
Method B & D blocked off 2 of 4 venturii

What were the typical test pressure drops?

When would it be important to flow a carburetor? I don't mean to sound ignorant. I'm just trying to understand the purpose.

Here I am think there was some dark hidden secret.
Like matching 2 carbs for a 2 x 4 tunnel ram.