Slant Six Forum :: CFM question

I was told the only difference between a 500 cfm and 600 cfm Eldebrock/Carter AFB was the booster size, same throttle bore and venturii. The bigger booster in the 500 would reduce the cfm but make the carb more responsive by giving a stronger signal. I don't have a Carter resource book, can anyone verify the 500 and 600 throttle bores and venturii?

Cecil

I agree on injection being the best thing, but for me, I'm looking for something of my own. I'm aiming for different and original. When the day comes where I am ata car show and the hood is raised, I want people to say - what the &$*#! is that? The , when they ask if it actually runs, I want to be able to start it up and drive home.

I don't know where you measure carb bore. If it is the bottom oopening where the butterfly is, I think it was 1 1/2" to 1 9/16" diameter. Perhaps turning in the mixture needles/screws would make it possible to run all six?

Dennis,

Where do you get a 400cfm carter? Is it off of a 273?

"Still, I think six stock one barrels on a slant six would be WAY too much carburation... I think three one barrels would be the $#!#. Set it up like a tri-power, run around on the center one for excellent throttle response and fabricate some progressive linkage that tips the outboards in at about 1/3 to 1/2 throttle (which you'll want to be able to adjust to your liking)."

Progressive linkage is what I was thinking. I know the 6 carbs is way too much for a slant normally, but I was hoping to lower the input from the 6 carbs so it could work. I'm thinking it would be much smoother running on 3 carbs with less fuel and air, than say a 1 barrel all by itself in the center. It's that whole distribution idea. I guess what I'm trying to say is that I'd like to have 2 cylinders running normally on 1/3 to 1/2 output with a secondary carb kicking in at the 1/3 to 1/2 throttle. The secong carb also running at a lower capacity.

You guys need to think ouside the box...

http://www.memorylaners.homestead.com/3x4intake.html

Author:	Dennis Weaver [ Mon Sep 08, 2003 9:29 am ]
Post subject:
Quote: I was told the only difference between a 500 cfm and 600 cfm Eldebrock/Carter AFB was the booster size, same throttle bore and venturii. The bigger booster in the 500 would reduce the cfm but make the carb more responsive by giving a stronger signal. I don't have a Carter resource book, can anyone verify the 500 and 600 throttle bores and venturii? Cecil I am away from home, and thus, away from my resources at the moment, but that very well does sound correct. I don't own one of the 500CFM carbs, so perhaps I can reference it somewhere. I can tell you that the bores on my 400 AFB are tiny, I believe I checked at one time and they are definitely smaller than the 500, but that's not to say that what you propose regarding the 500/600 is false. The 400 AFB was just a smidgen larger than the 390 holley on the primaries, I believe. "DW"

Author:	Dennis Weaver [ Mon Sep 08, 2003 9:47 am ]
Post subject:	Re: carbs vs injection; carb bore
Quote: I agree on injection being the best thing, but for me, I'm looking for something of my own. I'm aiming for different and original. When the day comes where I am ata car show and the hood is raised, I want people to say - what the &$*#! is that? The , when they ask if it actually runs, I want to be able to start it up and drive home. I don't know where you measure carb bore. If it is the bottom oopening where the butterfly is, I think it was 1 1/2" to 1 9/16" diameter. Perhaps turning in the mixture needles/screws would make it possible to run all six? Hell, run a Predator... I think if you're going to run 6 (barrels) you'd probably ought to go to a carb like a Weber sidedraft or the like. I know diddly-squat about those, but I think they are VV (variable venturi), right? I can tell you that the more venturii you apply to an engine, the more you can throw the common CFM requirement formula out the window, because you are increasing the venturi area at a different ratio than you would if you just kept making the carb bore sizes huge but kept the number of them the same. I have a street/strip 440 with an old purple shaft cam and two "550" Carter AFB's ("1100 CFM") set up to open progressively, and it runs great. The carbs dont even have the usual secondary air door to regulate flow on the secondaries. Still, I think six stock one barrels on a slant six would be WAY too much carburation... I think three one barrels would be the $#!#. Set it up like a tri-power, run around on the center one for excellent throttle response and fabricate some progressive linkage that tips the outboards in at about 1/3 to 1/2 throttle (which you'll want to be able to adjust to your liking). "DW"

Author:	mnecaise [ Mon Sep 08, 2003 2:03 pm ]
Post subject:
Dennis, Where do you get a 400cfm carter? Is it off of a 273?

Author:	mighty mouse 63 [ Mon Sep 08, 2003 2:16 pm ]
Post subject:	Where do I find
Pulled my 400cfm from a 63 corvette (duel quad set-up), believe they were popular during this time with them until the went to the dark side with rochesters. Reason I believe these to be factory is the GM style choke and the various GM part numbers stamped adove the carter numbers....Dave

Author:	kesteb [ Mon Sep 08, 2003 3:34 pm ]
Post subject:
Carter made aftermarket AFBs in 400 (9400), 500 (9500) and 625 (9625) cfm during the early '70s. They worked very well.They could be had in electric or manual choke models. After a few years they dropped the 9400, as nobody was buying them. I had a pair of 500s on a 318 with an Edelbrock dual 4v hi-rise manifold. It ran very well and certainly had the WTF going on. I ran various carb/manfiold choices on this engine and eventually settled for a LD340 and Holley 650 DB as the best performer.

Slant Six Forum https://www.slantsix.org/forum/

CFM question https://www.slantsix.org/forum/viewtopic.php?t=6820	Page 2 of 3

Author:	Dennis Weaver [ Tue Sep 09, 2003 12:42 am ]
Post subject:
Quote: Dennis, Where do you get a 400cfm carter? Is it off of a 273? Short answer: yes See related posts: http://www.slantsix.org/forum/viewtopic ... highlight= Mine is 4294S, originally for a '67 273 stick-shift. Here are some other numbers to try: 4295S 4304S 4305S 4119S 4120S 4121S 4122S "DW"

Author:	mnecaise [ Tue Sep 09, 2003 5:08 am ]
Post subject:
Now I know. Mwahahaha

Author:	Slanted73 [ Tue Sep 09, 2003 9:43 am ]
Post subject:	Re: Dennis - tri-power and progressive linkage
"Still, I think six stock one barrels on a slant six would be WAY too much carburation... I think three one barrels would be the $#!#. Set it up like a tri-power, run around on the center one for excellent throttle response and fabricate some progressive linkage that tips the outboards in at about 1/3 to 1/2 throttle (which you'll want to be able to adjust to your liking)." Progressive linkage is what I was thinking. I know the 6 carbs is way too much for a slant normally, but I was hoping to lower the input from the 6 carbs so it could work. I'm thinking it would be much smoother running on 3 carbs with less fuel and air, than say a 1 barrel all by itself in the center. It's that whole distribution idea. I guess what I'm trying to say is that I'd like to have 2 cylinders running normally on 1/3 to 1/2 output with a secondary carb kicking in at the 1/3 to 1/2 throttle. The secong carb also running at a lower capacity.

Author:	kesteb [ Tue Sep 09, 2003 1:04 pm ]
Post subject:
You guys need to think ouside the box... http://www.memorylaners.homestead.com/3x4intake.html

Author:	Dennis Weaver [ Tue Sep 09, 2003 1:22 pm ]
Post subject:
Quote: You guys need to think ouside the box... http://www.memorylaners.homestead.com/3x4intake.html Myself, I've never even seen "the box" up close... Maybe that's because I run when I see it coming... "DW" P. S. - Looking "sick" and running well do not alwez go hand-in-hand...

Author:	Charrlie_S [ Tue Sep 09, 2003 1:24 pm ]
Post subject:
I think that setup belongs to Larry Page, president of the Florida Inliners chapter. PS Slant Cecil and I are members.

Author:	Guest [ Tue Sep 09, 2003 2:29 pm ]
Post subject:
"An afterthought... Since you seem to like "gang" carburetion, what about a bunch of real tiny carbs from a non-automotive application? That'd be different fer sure.... Anyone have any ideas?" At a recent Mini club meet, I saw a 4 cyl mini (the original) with 4 very small carbs, almost looked too small to be motorcycle carbs. The guy said it ran 'smooth and fast'. I seem to recall the 6-packs only have the choke mech. on the middle carb. Makes things easier I reckon.

Author:	Slanted73 [ Wed Sep 10, 2003 8:43 pm ]
Post subject:	the gangs all here
I looked at the pick of the tri carb set up. That is what I started out initially. The reason I changed my design was the length of runners. To keep it under the hood, means either curving up and having short runners, or running the carbs over towards the driver side fender. I didn't want the carbs that far left. I guess I figured if it was going to stick above the hood, why not have the six pack look? I suppose it could still be cool with three carbs.

Author:	mustangsix [ Fri Sep 12, 2003 9:00 pm ]
Post subject:
We were having the same sort of discussion at FordSix.com. In my opinion, CFM alone is not always a good way to figure carburetion because it depends on so many factors. You cannot ignore # of cylinders, manifold configuration, or engine layout. For example, what is the cfm requirement for a single cylinder, 4-cycle, 225 cube engine, with 90% VE, running at 1 rpm? It's 213 cfm. Now why is it so different than a 225 six cylinder engine of the same displacement? Time. Thought the displacement is the same and the engine is only running a 1rpm, it needs the entire displacement all at once. By dividing the requirement and averaging it in a manifold over six cylinders you come up with a fairly low CFM requirement because you can spread the requirement out over time. But if you were to take six stock 1bbl carbs and mount one on each cylinder, you would probably be in the ballpark for carb capacity. This is because each cylinder only uses that capacity intermittently, not contiuously, so cubic feet per MINUTE takes on a different meaning. Though each cylinder has a small requirement over a minute's time at any given rpm, it is only inhaling air one large gulp at a time during small periods during that minute. This is why a triple 45DCOE setup might have a capacity of 1250 cfm, but works pretty well on a small 225 cube engine when set up with individual runners. Mount that much carburetion on an open plenum feeding all the cylinders, and you would have a dog. The same effect is noted when you look at other systems like Proline's dual carb manifold. Two webers might look like over capacity, but though each of those carbs is feeding fewer cylinders, they do so more intermittently over time. The logic might be hard to follow, but it is borne out in other designs like dual plane V8 manifolds. And as someone mentioned earlier, it's all apples and oranges when you look at the depression that the carb was rated at.

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