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Edelbrock/afb choke horn delete... #2679073
07/19/19 12:21 PM
07/19/19 12:21 PM
Joined: Jan 2003
Posts: 17,801
S.E. Michigan
ZIPPY Offline OP
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ZIPPY  Offline OP
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Seen a few with the choke horn cut off recently....

Is it really worth it?


Rich H.

Esse Quam Videri




Re: Edelbrock/afb choke horn delete... [Re: ZIPPY] #2679090
07/19/19 01:15 PM
07/19/19 01:15 PM
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Taxes & Virus's R-US, NY
Dragula Offline
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Anything that smooths or aids in air flow is worth it in a racing application. Free HP!


'70 Cuda,...605 EFI Hemi Street Car (6.20 best pass, 1.33 60ft)
https://www.youtube.com/watch?v=WYw6RA-k5Bk (6.25 at 108.75mph from inside car)
https://www.youtube.com/watch?v=3zQEb9uxFng (6.25 at 108mph from outside car)
https://www.youtube.com/watch?v=JCvfzsC4NgM (9.9)

'66 Barracuda AWB Stretched nose Blown 440 Car in build stage

'71 Duster Drag Car 400 Low Deck 512 best 6.002 at 115.44mph
https://www.youtube.com/watch?v=Znuo3jMUXTk
Re: Edelbrock/afb choke horn delete... [Re: Dragula] #2679097
07/19/19 01:39 PM
07/19/19 01:39 PM
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NE Ohio
DoubleD Offline
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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

Re: Edelbrock/afb choke horn delete... [Re: DoubleD] #2679099
07/19/19 01:43 PM
07/19/19 01:43 PM
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Wind Gap,Pa.
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Sammy Offline
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Wind Gap,Pa.
Theres no cutting involved.
Just unbolts

Re: Edelbrock/afb choke horn delete... [Re: Sammy] #2679108
07/19/19 02:32 PM
07/19/19 02:32 PM
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usa
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lewtot184 Online content
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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.

Last edited by lewtot184; 07/19/19 06:52 PM.
Re: Edelbrock/afb choke horn delete... [Re: lewtot184] #2679116
07/19/19 02:54 PM
07/19/19 02:54 PM
Joined: Jan 2003
Posts: 2,289
NE Ohio
DoubleD Offline
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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

Re: Edelbrock/afb choke horn delete... [Re: DoubleD] #2679322
07/20/19 08:14 AM
07/20/19 08:14 AM
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nielsville, minn.
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quickd100 Offline
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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.

Re: Edelbrock/afb choke horn delete... [Re: quickd100] #2680377
07/23/19 09:42 AM
07/23/19 09:42 AM
Joined: Jan 2003
Posts: 17,801
S.E. Michigan
ZIPPY Offline OP
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good info, thanks all.


Rich H.

Esse Quam Videri




Re: Edelbrock/afb choke horn delete... [Re: ZIPPY] #2680606
07/23/19 05:29 PM
07/23/19 05:29 PM
Joined: Mar 2009
Posts: 2,457
Sydney,Australia
tex013 Offline
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Zippy ,
I cut mine similar to a picture on Diamond's website .
Never ran them enough to see a definitive result

Tex


New best ET 10.259@129.65 .
New best MPH 130.32
Finally fitted a solid cam,
stepped it up a bit more
3690lbs through the mufflers
New World block 3780lbs 10.278@130.80 . Wowser 10.253@130.24 footbraking from 1500rpm
Power by Tex's Automotive
Re: Edelbrock/afb choke horn delete... [Re: quickd100] #2680632
07/23/19 06:39 PM
07/23/19 06:39 PM
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Aus
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hysteric Offline
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Originally Posted by quickd100
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.


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

Re: Edelbrock/afb choke horn delete... [Re: hysteric] #2680658
07/23/19 07:51 PM
07/23/19 07:51 PM
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Posts: 1,823
Wind Gap,Pa.
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Sammy Offline
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Originally Posted by hysteric
Originally Posted by quickd100
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.


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.

Re: Edelbrock/afb choke horn delete... [Re: Sammy] #2680687
07/23/19 09:06 PM
07/23/19 09:06 PM
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Aus
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hysteric Offline
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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.

Re: Edelbrock/afb choke horn delete... [Re: hysteric] #2680688
07/23/19 09:11 PM
07/23/19 09:11 PM
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Sobieski Wi
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bee1971 Offline
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Sobieski Wi
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






3F1351FA-24E8-4860-896F-3E59C23A91A4.jpeg
Last edited by bee1971; 07/23/19 09:16 PM.

1971 Dodge Charger Superbee
2011 Ram Sport 1500 Quad Cab Deep Water Blue Loaded
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Re: Edelbrock/afb choke horn delete... [Re: hysteric] #2680689
07/23/19 09:15 PM
07/23/19 09:15 PM
Joined: Mar 2006
Posts: 9,791
MI, usa
dvw Offline
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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

Re: Edelbrock/afb choke horn delete... [Re: DoubleD] #2780489
06/01/20 07:23 PM
06/01/20 07:23 PM
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CT
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Originally Posted by DoubleD
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


Who did your carbs?

Bill


1968 Road Runner 383 727 3.91 8 3/4 3520 with driver 11.04 @ 124.26 with 1.67 60’
Done on G70-14 redlines thru factory manifolds New quickest ever 383 build in FAST.
10:1 451” replaced with 14:1 499”.
Re: Edelbrock/afb choke horn delete... [Re: roadrunner2] #2780606
06/02/20 09:53 AM
06/02/20 09:53 AM
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MI, usa
dvw Offline
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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

Re: Edelbrock/afb choke horn delete... [Re: ZIPPY] #2780693
06/02/20 12:55 PM
06/02/20 12:55 PM
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Missouri
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jwb123 Offline
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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.

Re: Edelbrock/afb choke horn delete... [Re: dvw] #2780804
06/02/20 04:31 PM
06/02/20 04:31 PM
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Downtown Roebuck Ont
Twostick Offline
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Originally Posted by dvw
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


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

Re: Edelbrock/afb choke horn delete... [Re: Twostick] #2781632
06/05/20 10:23 AM
06/05/20 10:23 AM
Joined: Jan 2003
Posts: 17,801
S.E. Michigan
ZIPPY Offline OP
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Nice info shared here, thank you for reviving the old thread to whoever did it.


Rich H.

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