Edelbrock/afb choke horn delete...

Seen a few with the choke horn cut off recently....

Is it really worth it?

Anything that smooths or aids in air flow is worth it in a racing application. Free HP!

AFB's are a funny carb when trying to mill the air horns off as they do not respond like a Holley will. Unless you have hood clearance issues I would not do it - you will find no real gain and if not done correctly it can cause a fall off on performance. The air bleeds on the AFB are extremely sensitive to disruption of air flow. We typically remove the choke completely for racing and lighten the air door weight a little and then change the jets, rods and springs to tune it in. We have several sets of milled and un-milled AFB and AVS and they will perform pretty much equal - but hood clearance is the key with an AFB as you need about three inches as a minimum or they can really get strange in the fuel curve. And the K&N stub stack for AFB's will absolutely cause problems.. You can clean - up all the casting marks and smooth them out and then polish the boosters that helps with air flow

Theres no cutting involved.
Just unbolts

I've played with a bunch of the AFB re-pops these past few years. I really don't think air flow is as big a problem as fuel supply. chasing air flow is part of the holley culture (and these carters are a different animal vs holley), but what good is a bunch of air if there's not enough gasoline?

when I say "fuel supply" i'm not referencing jet or metering rod size. it's the internal fuel passages, emulsion tubes, and booster discharge tubes. seems like they have been down sized from the original old carter carbs and the internal machining isn't as nice. I don't think the new stuff will flow the fuel that the old stuff will. I do think because these carbs are "fuel" challenged lends to my belief that they run better in pairs than singlely. running in pairs reduces the fuel flow burden drastically per carb. both my cars use carter types. one is single carb the other dual. I know from working with the single carb setup (stock 375hp 440) the factory avs has larger passages, emulsion and discharge tubes and performs better than a 1407 edelbrock. there shouldn't be a major difference between the two if air flow mattered. the 1407 won't drive if jetted the same as a stock '67 440 carb which has the same throttle bore and venturii as the 1407. throw a lot of jet at the 1407 and it will drive ok, burn decent at cruise, but won't perform with the avs. so what's the real difference? air flow is about the same; got to be internals, and I don't mean jets.

Fuel never seems to be an issue for us as of late - with big CI engines we normally have to jet them down 1 or two steps both primary and secondary from stock - a good fuel pump and dual feed with the big needle and seats seems to solve the fuel flow issue -along with running the floats a little higher. I prefer the 800's on my 572 it was a huge difference on the Dyno. We do have one set of heavily modified that flow around 1000 CFM each - I have not tried them yet but they show promise

I agree with Double D. The newer Eddie's don't have large enough passages to flow enough flow to match high air flow demands. When you have to jet down like that the carb is to small for the application.
I did some carb testing on the dyno a while back using a 11.8-1 426 wedge. I started with a 600 Eddy, I had to jet DOWN many sizes as it was Dead rich. Once I got it to 12.5-13.0 a/f and made a couple pulls you could tell the motor was struggling. Best pull with the 600 was 444hp and 386.1ftlbs. I installed a 750 Eddy and only had to drop one or two jet sizes and it made 463.8hp and 508.5 ftlbs. Going to a 850 double pumper the jetting was spot on.

good info, thanks all.

Zippy ,
I cut mine similar to a picture on Diamond's website .
Never ran them enough to see a definitive result

Tex

There are a few issues with the Edelbrock/Federal Mogul AFBs. The restriction in the secondary booster's is discussed here:

Edelbrock 1407 booster discussion Speed Talk

Also the original 750 AFB Carter carbs have a different length booster which places it correctly just below the vena contracta. Edelbrock and Federal Mogul use the 625 carter booster in the 750 which is too short and delays the onset of primary booster flow.

The older Carters have a better sized and placed emulsion package. Easiest thing to do would be to find an old 750 carter and place the boosters in your Edelbrock carb.

Hope this helps

Hysteric

You are exactly correct.
I did back to back dyno pulls with old Carter Competition 750 AFBs vs. The new 800 Edelbrock AFB and the new Edelbrock outperformed the old 750 Carter by over 26 HP.
I'm going to switch secondary boosters next to see how much more I can pick up.
The dyno was with 2 AFBs on a inline Indy Tunnel ram.

I swapped from a modded top plate 750 Edelbrock AFB to an 800 AVS and picked up 2 tenths in the 1/4 on a mild 360.

This - 800 AVS 2

Man this carb is awesome so far

Going to pull off the choke plate and linkage this weekend - Never used it or need it

383/432 Stroker

75cc E Street Heads
Comp XE 275HL

I run a pair of nearly stock 750 Eddy's. No choke plate, dual inlet. Car has been tested with 800 Eddy's and Pro System 750 Holley's as well. Currently it has K&N stub stacks to smooth the air entrance (still testing). The difference between all of them? I haven't seen .05 in ET. This on a motor that has run a best of 150mph@3350lbs
Doug

Who did your carbs?

Bill

Been trying the stub stacks almost an entire season. I did add bowl vent tubes. My theory was that the air flow wentover the stock vent holes dropping bowl pressure. For sure they have a better shape than just cutting off the choke horn. It helped in the early part of the run. 660 mph gained close to 1mph.
Doug

I race NSS, and the main reason I cut the choke horns off is to get more clearance on the front carb to the top of the scoop. I like to run the close to original scoop, not the over sized ones, and if you don't have the three inches clearance, my car will slow down.

I set my carb on the flow bench and started cutting and checking things, I got about 5 CFM by cutting off the choke horns, my bench would only pull them to 10 inches of water, and then I just converted to 20 inches, which I think is close to the 3 inches of mercury the carbs are rated at. my 750's flowed 670cfm on the bench at 20 inches. I do know that if you cut too much off the horn, you get a lot of turbulence around the top of the venturi's. So I just cut and kept checking with a wand with a string until I had a decent nonturblent flow into the venturi's. That wound up being about 1/4 inch taller than the ring where the air cleaner would sit.

I think the biggest improvement on my carbs was to use the velocity probe on my bench and solder a carb jet to a brass tube, and measure the flow or pull on the venturi, both primary and secondary, then swap clusters and/or polish them until they are all balanced as close as you can get them. I also pressed on a thin aluminum sleeve to extend the front venturi deeper into the body, like the older boosters were. My results were Front venturi’s flow tested at 10 inches, 194 to 198 feet per second on velocity manometer
Longer sleeves added to improve flow, improved to 220-229 feet per second velocity.

I got to run the car this weekend and the O2's showed a lot more steady AFR during the run than the other carbs I have used. And the engine made more power than I could reliably hook. Got it to run a 6.15 @ 112 mph spinning the tires with only a 1.40, 60 foot. in the 1/8 mile. On an easier run when I stalled at less rpm, it pulled a 1.33, 60 foot. So today I ordered some different rear springs, to loosen it up a little.

My machinist uses those on his 2.5 liter hydroplane engines that run 500 Holley 2 barrels. He plays with the profile on the flow bench to max it out.

It makes a statistically significant difference on the dyno.

Kevin

Nice info shared here, thank you for reviving the old thread to whoever did it.