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.