Increasing carb cfm

I’m limited in my class to a single Edelbrock 800 cfm carb. What are my options to get more flow?

Thanks.

Bill

Bill I read an article once on reducing the OD of the (2) horizontle booster legs & reducing the dia of the choke shaft & as far as removeing it, John the carb guru at "the carburetor shop" says its better to keep it installed as it straightens the air flow & is very beneficial. Another tidbit was to use another gasket under the booster cluster to raise it for more airflow & shortening the vertical boosters. Can you enlarge the venturis bore(s) & booster nozzles, their ID? EDIT I heard that that round black plastic airhorn piece that I think Holley sells helps straighten the airflow & is good. I would give John a call & he only takes calls on Mon/Tues, I dont have his # handy but you can Google it. He's the man on this stuff

All internal mods are good. Carb must look stock on the outside.

Thanks for your input.

All internal mods are good?

How much money do you want to spend?
Boring the body oversize and installing larger throttle discs is 90 years old TIKO.

Are you limited on the intake type and mods? How about the camshaft limits Many ways to trick a motor into making more power, carb spacers, single plane intake, making the plenum bigger and so on

I've seen ore than a few modified ones running in N/SS. To be honest they haven't shown much improvement. The AFB style can use a stub stack. But we've tried one modified to fit and AVS and went slower. You can do the usual stuff. Thin the boosters (seen them break off). Streamline the throttle shafts.
Doug

I have to use the factory cast iron intake. Internal mods are allowed and have been done. No spacers allowed. Using a custom solid flat tappet now, switching to a roller this off season. 👍🏽

Bill

That’s kinda where I’m at now. Maybe Edelbrock will make a 1000 cfm carb someday. 🤔

I think trying to increase cfm is irrelevant. increasing venturii area may help. thinning the boosters may delay main circuit discharge. you really need to think about what 800cfm is, what it will feed, and keep in mind that cfm ratings in real world applications don't mean that much. the carb is rated at 800cfm at 1.5"hg pressure drop. attach a vacuum gauge to the carb or manifold the next time you make a pass and see if your any where near 1.5"hg at WOT, then make an informed decision about what to do next.

Talk to Damon Kuhn, see what he can do.

http://www.diamondbackengines.com/index.php/our-carburetors

I picked up a couple of tenths.

John Kaase: "that's not a spacer, it's a base gasket".
The difference? He's important.
I think anything thick enough to matter will be detected.

Just based on laws of physics: we radius the bottom of the manifold's plunge into the plenum (I did very "directional" work inside my 383/343 HP 2 X 4 factory manifold based on the direction and proximity of the ports being supplied). I'm tempted to radius the carburetor exit below the base where it's not accurately placed on the manifold, or hanging above a machine cut. Taken many apart to feel a 1/16" ledge in places. In general, any surface interruption is a trip wire, and air stumbles and slows down as it goes past.
Care to share any info/pictures of your manifold interior??

Haven't inspected your carb, the main venturis are the intersection of 2 angles. Is their transition sharp or radiused? A small radius will improve flow, but try to avoid moving the "vena contracta" (smallest point) which is located about 1/32" above the booster discharge. Both ends can be enlarged at the same angle (steep on top, shallower below) making a smaller triangle with the same angles to increase venturi ID but it's Impossible to get in there. Easier to bore them out (yes, take the whole thing part) and make an insert. Much, much time for small gain.

Any re-shaping of the air horn, even intuitive blending the sharp edges, makes me very nervous: the factory calibration of air bleeds, blah is based on what happens there, and more CFM may upset the transition. Vizard has warned about this (but not specifically the Edelbrock IIRC).

As a point of reference, a bigger cube motor than the OP’s, that ran in the same series built to a much higher level(no disrespect, just is it what it is), that made what I’d estimate is roughly 100hp more........ only used 730cfm@6100.

If you want to know “how much” ET is left on the table with a carb, from either a calibration or capacity standpoint, borrow something like a Holley 850 or 950 from someone and see what kind of improvement there is.

On another build for that same series, also bigger cubes....... there was basically zero difference on the dyno between a Holley 750dp with the choke removed vs an Eddy 800.
That motor used 720cfm @6500

Motors of this type, in legal trim.......are going to be down about 100hp+, compared to what you’d see out of a comparable bracket build would make.

That being said, we tried a correct 383 avs on one of the motors compared to the Eddy 800, and it was down about 30hp.

I should’ve just called you.
Also I’m going for that 383 record next year. 👍🏽

383........ or “383”?

I think the “383” record is around 11.50....... and there was def more left in that combo if he’d have stuck with it.

“383”. That’s the one.

a correct 383 avs

Rated 480 CFM, same for the 340, 580 for the 440, IIRC

Dale Cubic at CFM carbs probably knows as much as anyone about these units.
Doug

120mph is 6-pack territory in a B-body...How much did the dart weigh with Jim in it?

I don’t know what one of those weighs, but I don’t think his had any major lightening done to it, plus it had the added weight of the roll bar.
It’s still an all iron big block with ex manifolds and full ex system, steel wheels, etc.
His is a bucket seat car...... originally a 4 speed.
I actually think it went 122-ish with the stick.

The fastest of the 6bbls went either 129 or 130, and that was at 3900lbs.
Number two was 127 iirc.