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.

Is it common for carbs to be off much from their advertised cfm?

Neat testing,Brad! You are thinking outside of the bun again! But come on....Put the damn thing together already!!

I did this for myself, not for Moparts, but am still a bit surprised by the lack of any related comments.

Is the lack of response to this post (despite over 1000 hits) due to the what seems to be a continuing trend on this forum that "tech is boring", or because all of about four people on this board thought this data was even worth discussing?

I did find it interesting!

Well its easy to be interested. That is why so many views. Its harder to understand what is being done. Myself included. When I see flow data it is usually cylinder heads.

Brad,
thanks for the post/info.i guess it does show that you can only compare carbs based on their specifications,venturi/throttle size,not what the manufacturer calls them

Tex

I too find it interesting, and appreciate the info, but don't know what to make of it either.

I've wondered about the 1.56/1.60 venturi 4150 carbs, and the flow restriction contribution from the throttle shaft and throttle plate. Ideally, the only restriction would the venturi and booster. So, I would find it interesting to see the same tests without the shafts/plates. Not sure what the value of that would be either.

I was looking all over the web for this info, it was right here the whole time.
Thanks BradH for doing this test!

Same here.

When I made my flow bench I used a 4150 pattern to mount my bore adapter to. So I have just flowed carbs all 4 bbls all at once.

One day Im on the phone with Eddie Miller, he is telling me he is putting 2 90mm throttle bodies on his tunnel ram. Says they flow 1100 cfm each. Im like BS, no way. Hold on, I have a 90 here. Throw it on my bench. 1086. Wow. Ok

On the phone with Thumper, i ask him what a particular carb I have is supposed to flow, he said he thinks 1200. I throw it on the bench and it reads 1168 or something. Ok

You just tested a bunch on the dyno which seems to be a much better indicator of what might work best unless to much data has you scratching your head from that test session

When I flow a carb, I test all barrels individually, then add the numbers together.

4bbl carbs are rated at 1.5"hg test pressure, which is like 20.4"h2o.
I could probably pull 20.4" of pressure flowing 2bbls at a time for most 4150 carbs, but I'd have to make a different fixture to do it that way.

I very rarely flow test carbs anymore.
Pick the size you feel you need....... Then most of the power is in the metering.

To that point:


Of the carbs we ran on Brads motor, only one had the metering off far enough where we couldn't make pulls without fear of doing some damage.
Of the other carbs tested, the one with the smallest venturi(and least flow) made as much power as any of the others.
It was doing a better job of mixing the fuel.

I wish someone would build a billet carb base that has a built in shear plate bottoms...maybe you could test a shear plate vs a regular carb bottom?

Just caught this thread.
Ever considered flow a couple of TQ’s?

i really like those carbs, and that would be of interest to me as well.

Sorry folks, but this is really old data... 5 years. I won't be doing any carb flow bench testing in the foreseeable future, nor do I have a spreadbore test fixture for a TQ.

It would be interesting to know what the actual flow is of the different aftermarket main bodies available. That would be some great data.........

If you want what I would consider even close to "accurate" flow data from carbs, they really should be flowed with all barrels at the same time, at full capacity(1.5"hg).
And that means you need a big honkin flow bench.

And even better yet....... Wet flow tested.

The Super Flow carb testing fixture is pretty similar to what Brad used, only it comes with a 4 hole spacer.
The spacer has a small hole in the center of it to locate it on the pin in the plate.
Then you just rotate it around to test all 4 holes.

The hole in the plate is 1.750, but the holes in the supplied spacer are only 1.687, which is fine if you're testing carbs that don't have a 1.750 throttle bore.

I found a spacer with 1.750 bores to use on the big carbs, and drilled the hole to locate it on the pin.

I also made one to use with 4500 series carbs.

found this on the www http://www.ryanbrownracing.com/Bill_Jones_Page_4.html

I just threw one on my bench and it said 820cfm

Ray, could you pull 20.4" with flowing all barrels?

IDK. Im sorry but I have no idea.

I just threw my 1050 dominator that had the boosters changed to skirted boosters for e85 and it says it flows 1000.

Well, i just tried a 600cfm performer and it says 670cfm.

My method is probably not accurate but I would think comparable for me checking different carbs

You don't know what the test pressure is?

Edit:
Okay, I looked at the site where you got your electronics from.
The picture of the display box isn't all that clear.

Is one of the options for the display 20.4"?
If not, are you using one of the other depressions and converting the numbers to 20.4"?

Thanks. What model number & primary size?

Thanks as well sixpac ! same question as rob.

Guys, I really dont think the way Im doing this is accurate. Im just throwing it on the bench with it converting at 28".

The TQ I have is 9379s. Pri 1.370

Edit: fast68 is schooling me on flowing carbs. My numbers are not accurate and he is making me depressed. lol