THREE AFBs?

Discussion of the 331-354-392 HEMIs.

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NE57
Posts: 192
Joined: Fri Mar 27, 2009 12:54 pm

THREE AFBs?

Post by NE57 »

I heard mention of using 3 AFBs on a 392. Was this ever a reality? Must look wicked but how well could it/did it run?

Talk about automotive eye candy huh?
DRHEMI
Posts: 15
Joined: Mon Jun 08, 2009 11:30 am

Re: THREE AFBs?

Post by DRHEMI »

Some time back, one of the many Mopar magazines published a photo of a 426 Hemi superstock cross-ram manifold with mounting pads for 4 (Four) AFB carbs. It was from the mid-60s, an engineering exercise, I recall. Must not have tested well, for I don't ever recall seeing any mention of the manifold ever being successfully used.
-Andy Carlson
Ojai CA
mart
Posts: 536
Joined: Tue Mar 22, 2005 2:06 pm

Re: THREE AFBs?

Post by mart »

The only place I've seen three AFBs actually used on an engine was on top of a 6-71 blower. 'Back in the day', circa 1967-68 -69, a neighbor of ours had a 394 Olds-powered '39 Chevy gasser that he experimented with a couple different home-brew carb set-ups on . The first set-up he played with was three 394 Olds Rochester 4GCs on top of the blower and then later, he switched to three Carter AFBs. Holley's wouldn't fit unless they were mounted sideways, but the Rochester 4GCs and Carter AFBs, having their float bowls integral with the carb bodies, are just physically small enough that, butted end to end, so the carb bodies almost touch each other, three of them will just fit on top of a 6-71. I think once he got it sorted out it, both of the 'triple 4-bbl' set-ups worked fairly
well...not to mention, looking absolutely outrageous and cool as hell! :)

mart
=========================================================
NE57
Posts: 192
Joined: Fri Mar 27, 2009 12:54 pm

Re: THREE AFBs?

Post by NE57 »

>absolutely outrageous and cool as hell!

so then...you wouldn't think I'm stupid to maybe give it a try? I've got two 400cfm AFBs so three would be 1200 cfm, a bit much by standard theory but six pack setups have more than that even on just 340CI, which I never did understand. But it'd be much easier to make a 3 carb inline manifold than a 2 carb crossram, which I've given alot of thought to.

Anyone else like to thumbs up or thumbs down the idea of a 'twelve pak'??
mart
Posts: 536
Joined: Tue Mar 22, 2005 2:06 pm

Re: THREE AFBs?

Post by mart »

NE57 wrote:>absolutely outrageous and cool as hell!

so then...you wouldn't think I'm stupid to maybe give it a try? I've got two 400cfm AFBs so three would be 1200 cfm, a bit much by standard theory but six pack setups have more than that even on just 340CI, which I never did understand. But it'd be much easier to make a 3 carb inline manifold than a 2 carb crossram, which I've given alot of thought to.

Anyone else like to thumbs up or thumbs down the idea of a 'twelve pak'??
-------------------------
I think it could made to work quite nicely. Here's why. First, you could run progressive throttle linkage, similar to what is used a lot
of 3-2bbl set-ups - so that at idle, and up until about 3/4 throttle,
the engine would only operate on the center 4-bbl. Additionally too, the secondaries on AFBs are actuated by airflow (and this setting and the amount of airflow required to open them is adjustable) so that most of the time you'd actually only be running on the primary side of the center carb anyway. Beyond 3/4 throttle the primaries of the end two carbs would come come into play, but even then, assuming they were properly adjusted, the secondaries on all three carbs would not open up until the engine actually required more airflow than the three sets of primaries where providing.

mart
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Last edited by mart on Thu Mar 11, 2010 12:57 pm, edited 2 times in total.
timshemi
Posts: 16
Joined: Sat Dec 12, 2009 10:58 am

Re: THREE AFBs?

Post by timshemi »

here is the one drhemi was talking about. pretty neat a 16 pack!
http://www.moparmusclemagazine.com/tech ... index.html
NE57
Posts: 192
Joined: Fri Mar 27, 2009 12:54 pm

Re: THREE AFBs?

Post by NE57 »

Wow that 4x4 is impressive looking. I've been checking into flow rates of AFBs and while certainly still a rookie I'm thinking 400CFM carbs for the street is the ticket rather than 500 and up carbs, in multi carb setups that is.

I found this online...

CFM Venturi Diameter Bore Diameter
primary secondary primary secondary
--------------------------------------------------------
400 1 1/8 1 1/4 1 7/16 1 7/16
500 1 3/16 1 1/4 1 7/16 1 11/16
575 1 1/4 1 9/16 1 9/16 1 11/16
625 1 3/16 1 9/16 1 7/16 1 11/16
750 1 7/16 1 9/16 1 11/16 1 11/16

The 400cfm has the smallest primary venturi. Logic might suggest that this will help signal strength and therfor general throttle response and driveability. I think the trick would be the transitional stages, so that each next set of throttle blades don't suddenly bog the motor. This sounds like a lot of fun..or heartache!
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