What Carburetor for Factory 4-bbl?

And this is maybe a little 'beyond' the original posted question,

but what brand and size carburetor to use can be a loaded question...

imho best for an individual to learn a little about the 'marketing claims' and their shortfalls,

then make an individual informed decision... I focus on Butterfly and Venturi Diameters more that claimed CFM Ratings.

This is the part saved as text from the now defunct other forum, then after that is an image file of the chart Ken Parkman compiled:

Ken_Parkman

Carb flow test

02/09/08 at 22:39:45

For various reasons there seems to be a lot of carburators

around here right now, so I decided to put them

all on the flow bench for comparison.

My flowbench cannot effectively measure a carb cause to do it right

you need to have a bench that will suck the roof off the shop and

has a direct power supply from the generating station.

But what I can do is run the bench wide open and then put on different carbs

and measure the pressure drop, and then I can compare one to another.

I could check an individual barrel, but that takes fixtures

I don't have and can't be bothered making.

As you know there is way more to carbs than flow - a point that

has really been hammered home to me with some dyno and track testing.

Also as you know factory ratings are pretty much meaningless

cause they are marketing more than anything. So this is an effort

to see how much some manufacturers are exagerating. Do not use this

data to say one will make more or less power; it's only for interest.

So here is the list of different carbs and their ranking

flow wise, smallest to largest:

Rank/Carb/part number/rating/comments

1 Edelbrock 1405 600

2 Holley 1850 600 Significantly more flow than Edelbrock 600

3 Q-jet ? ? Secondary air flap has a stop to limit opening

4 Holley 4777-2 650

5 Edelbrock 1407 750 Slightly more than 650 Holley

6 Edelbrock 1813 800 Big improvement over 750 Edelbrock

7 Q-jet ? ? Secondary air flap opened noticably more than above Q-jet

8 Holley 4780 800 Same dimensionally as a 750,

but this carb had a slight TB mismatch.

9 Holley 3310 780 Factory GM original 3310, down leg booster

10 Holley 3310-2 750 Strait booster than above, flows a little better but close

11 Pro-Systems XC ? Built for a mild 327 Chev, noticably more flow than above Holleys

12 Holley 4781 850 No choke plate

13 Holley 80514 1000 Annular booster carb, very small flow difference from 850

14 Pro-Systems XE ? Down leg booster, very significantly more flow than 1000 Holley

A couple of comments:

The Edelbrocks flow significantly less than the same rated Holley

Holley plays games with flow ratings.

Yes a 750 Holley flows more than a Holley 800.

I've heard it before, but this seems to confirm

a 850 holley is a lot bigger than a 950.

Dimensionally the 850 is bigger.

The 850 with no choke and a stubstack was essentially identical

to the annular booster 1000.

Stubstacks noticably improve the flow.

A fancy cnc milled 2" spacer slightly improves the flow.

The Q-jets were flowed with an adapter that slightly restricted the flow,

but calibrating with a holley says the resriction was not much.

I'm going to try to get a few more carbs to add to this list,

including a factory AFB and Motorcraft.

-------------------------

Ken_Parkman

Re: Carb flow test

Reply #6 - 02/10/08 at 17:10:59

Trying to find some stock AMC stuff, just don't have any here!

I hope to score a stock AFB and a 4300 to test, I'll post if it happens.

What Reagam said is important. A high flow carb is no good

if it can't properly atomize fuel at a low delta pressure.

Only take this data as an interesting comparison.

Of course a really good carb is both high flow and

can properly control the mixture at a wide rpm and load range.

A simple flow test cannot tell this.

--------------

Ken_Parkman

Re: Carb flow test

Reply #8 - 02/16/08 at 18:22:16

Those were 2 different stubstacks, both K & N.

One is very old (been through a carb fire)

and has been modified to better fit the 850,

which seems to have a different height air horn

then the stubstack was designed for.

The other is an almost new one made from

a different plastic and fit the 750 very well.

Both noticably improved flow,

but clearly the bigger 850 really liked it, the flow was well up.

The spacer is a really trick cnc milled 4 hole

translating to an open with a nicely faired 'bullet' in the center.

But now that I am carefully looking I find it has slightly small bores

on the 4 hole part. I'm gonna fix that and try again.

Just scored a couple of Demons, a good prepped dyno 750 holley,

and a stock AFB. Hope to have a Motorcraft

and a few more Holleys tomorrow. Will post info

-------------

Ken_Parkman

Re: Carb flow test

Reply #14 - 04/28/08 at 02:32:16

I FINALLY managed to score some stock AMC carbs

and get all the data together. I've had 29 carbs

accross the flow bench and it is an interesting exercise.

I've learned carb flow numbers are a game.

Do not assume a carb is bigger because it it rated higher.

The highest flow 750 carb was 150 cfm better the lowest flow 750.

A surprise is the stock Motorcraft 4300.

I scored a OWA4-S, and it's surprisingly good flow wise.

It looks crappy, but flows a tiny bit better

(not enough to give a number)

than a Demon 625 or an Edelbrock 600, both of which are pretty much the same.

A Holly 600 is about 40 cfm better than the BG and the Ed.

The stock AMC AFB (tested # 4664) is about 40 cfm less

than the sam BG and Ed Carbs. The Ed 600 is an AFB and is basically

the same carb as the stock AFB. It has the same bore's and venturi's,

but the Ed has 1/2 throttle shafts and a little aerodynamic fairing

to account for the 40 more cfm.

The 4350 Motorcraft is the same as the stock AFB.

I scaled the carbs on a 0-100 scale, and here are the small carbs

Edelbrock 750 (1407) - 71

Holley 700 (4778) - 71

Holley 650 (4777) - 69

Rochester Q-jet (xxxx) - 67 (small one)

Holley 600 (1850) - 65

Motorcraft 4300 (xxxx) - 61 (OWA4-S)

Barry Grant 625 (xxxx) - 61 (Road Demon)

Edelbrock 600 (1405) - 61

Carter AFB (4664) - 57

Motorcraft (4350) - 57

---------------

(4) MORE POSTS ON PAGE 2 -> BUT NOT ON WAYBACK MACHINE !

-------------------

-> ( 14 ) POSTS REPLIES ON PAGE 1 - SAVED HERE ALL post BY KEN PARKMAN

( 4 ) MORE POSTS ON PAGE 2 -> BUT CARP! I CAN'T FIND!

NOT ON WAYBACK MACHINE !

-> Today, Wed, Feb 20, 2019

-> post on Billd Forum to Ken Parkman asking for missing text

-----------------

crap ! PAGE 2 WAS not SAVED BY WAYBACK MACHINE !

And this is the image, hope it is legible, have yet to take time to type it up:

Edited by PHAT69AMX - Feb/13/2020 at 9:59pm

Link to a Short YouTube Burnout Video

It you just want a new bolt on carburetor that works - the Summit Brand Crabs people say are good.

They are just a rebranded Holley design from the 80's, and are low cost.

If you are ok with rebuilding and tuning a carb, get a used holley list 1850 for $50 off MarketPlace.

Getting pieces and parts and 'input', ha, for the 1850 Holley will be easy.

All also available for the MotorCraft AutoLite but less readily, maybe more costly,

a new float for that is high dollar from what I understand, and the Dual Inlet Needle set-up

can be tricky to get correctly set-up, some web sources show blocking off the 2nd Inlet Needle.

For the Spacer, finding stock will be less than easy.

Aftermarket carbs most likely will already have the needed hose connections

that were in the stock spacer since the stock MotoCraft AutoLite lacked them.

Square Flange 4-hole Carb Spacer of a material, brand, height, of your choice,

some folks even make them out of wood at home.

Link to a Short YouTube Burnout Video

Author	Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic
Ken_Parkman Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1814	Post Options Post Reply Quote Ken_Parkman Report Post Thanks(1) Quote Reply Posted: Feb/13/2020 at 9:17pm
	OK by me. Probably a really good idea, cause I read my chart wrong. And maybe you should not believe me! Sorry about that. The 4300 is actually bigger than a 600 Edelbrock, my mistake was reading the line with a stub stack. But they are very very close, along with the 625 BG. The 600 Holley 1850 is noticeably bigger though than all 3 of those. I've decided carb flow numbers are a bit of a marketing game - tracked a huge variation in 750 carbs, even within the same manufacturer. Edited by Ken_Parkman - Feb/13/2020 at 9:27pm

PHAT69AMX Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926	Post Options Post Reply Quote PHAT69AMX Report Post Thanks(0) Quote Reply Posted: Feb/13/2020 at 9:49pm
	And this is maybe a little 'beyond' the original posted question, but what brand and size carburetor to use can be a loaded question... imho best for an individual to learn a little about the 'marketing claims' and their shortfalls, then make an individual informed decision... I focus on Butterfly and Venturi Diameters more that claimed CFM Ratings. This is the part saved as text from the now defunct other forum, then after that is an image file of the chart Ken Parkman compiled: Ken_Parkman Carb flow test 02/09/08 at 22:39:45 For various reasons there seems to be a lot of carburators around here right now, so I decided to put them all on the flow bench for comparison. My flowbench cannot effectively measure a carb cause to do it right you need to have a bench that will suck the roof off the shop and has a direct power supply from the generating station. But what I can do is run the bench wide open and then put on different carbs and measure the pressure drop, and then I can compare one to another. I could check an individual barrel, but that takes fixtures I don't have and can't be bothered making. As you know there is way more to carbs than flow - a point that has really been hammered home to me with some dyno and track testing. Also as you know factory ratings are pretty much meaningless cause they are marketing more than anything. So this is an effort to see how much some manufacturers are exagerating. Do not use this data to say one will make more or less power; it's only for interest. So here is the list of different carbs and their ranking flow wise, smallest to largest: Rank/Carb/part number/rating/comments 1 Edelbrock 1405 600 2 Holley 1850 600 Significantly more flow than Edelbrock 600 3 Q-jet ? ? Secondary air flap has a stop to limit opening 4 Holley 4777-2 650 5 Edelbrock 1407 750 Slightly more than 650 Holley 6 Edelbrock 1813 800 Big improvement over 750 Edelbrock 7 Q-jet ? ? Secondary air flap opened noticably more than above Q-jet 8 Holley 4780 800 Same dimensionally as a 750, but this carb had a slight TB mismatch. 9 Holley 3310 780 Factory GM original 3310, down leg booster 10 Holley 3310-2 750 Strait booster than above, flows a little better but close 11 Pro-Systems XC ? Built for a mild 327 Chev, noticably more flow than above Holleys 12 Holley 4781 850 No choke plate 13 Holley 80514 1000 Annular booster carb, very small flow difference from 850 14 Pro-Systems XE ? Down leg booster, very significantly more flow than 1000 Holley A couple of comments: The Edelbrocks flow significantly less than the same rated Holley Holley plays games with flow ratings. Yes a 750 Holley flows more than a Holley 800. I've heard it before, but this seems to confirm a 850 holley is a lot bigger than a 950. Dimensionally the 850 is bigger. The 850 with no choke and a stubstack was essentially identical to the annular booster 1000. Stubstacks noticably improve the flow. A fancy cnc milled 2" spacer slightly improves the flow. The Q-jets were flowed with an adapter that slightly restricted the flow, but calibrating with a holley says the resriction was not much. I'm going to try to get a few more carbs to add to this list, including a factory AFB and Motorcraft. ------------------------- Ken_Parkman Re: Carb flow test Reply #6 - 02/10/08 at 17:10:59 Trying to find some stock AMC stuff, just don't have any here! I hope to score a stock AFB and a 4300 to test, I'll post if it happens. What Reagam said is important. A high flow carb is no good if it can't properly atomize fuel at a low delta pressure. Only take this data as an interesting comparison. Of course a really good carb is both high flow and can properly control the mixture at a wide rpm and load range. A simple flow test cannot tell this. -------------- Ken_Parkman Re: Carb flow test Reply #8 - 02/16/08 at 18:22:16 Those were 2 different stubstacks, both K & N. One is very old (been through a carb fire) and has been modified to better fit the 850, which seems to have a different height air horn then the stubstack was designed for. The other is an almost new one made from a different plastic and fit the 750 very well. Both noticably improved flow, but clearly the bigger 850 really liked it, the flow was well up. The spacer is a really trick cnc milled 4 hole translating to an open with a nicely faired 'bullet' in the center. But now that I am carefully looking I find it has slightly small bores on the 4 hole part. I'm gonna fix that and try again. Just scored a couple of Demons, a good prepped dyno 750 holley, and a stock AFB. Hope to have a Motorcraft and a few more Holleys tomorrow. Will post info ------------- Ken_Parkman Re: Carb flow test Reply #14 - 04/28/08 at 02:32:16 I FINALLY managed to score some stock AMC carbs and get all the data together. I've had 29 carbs accross the flow bench and it is an interesting exercise. I've learned carb flow numbers are a game. Do not assume a carb is bigger because it it rated higher. The highest flow 750 carb was 150 cfm better the lowest flow 750. A surprise is the stock Motorcraft 4300. I scored a OWA4-S, and it's surprisingly good flow wise. It looks crappy, but flows a tiny bit better (not enough to give a number) than a Demon 625 or an Edelbrock 600, both of which are pretty much the same. A Holly 600 is about 40 cfm better than the BG and the Ed. The stock AMC AFB (tested # 4664) is about 40 cfm less than the sam BG and Ed Carbs. The Ed 600 is an AFB and is basically the same carb as the stock AFB. It has the same bore's and venturi's, but the Ed has 1/2 throttle shafts and a little aerodynamic fairing to account for the 40 more cfm. The 4350 Motorcraft is the same as the stock AFB. I scaled the carbs on a 0-100 scale, and here are the small carbs Edelbrock 750 (1407) - 71 Holley 700 (4778) - 71 Holley 650 (4777) - 69 Rochester Q-jet (xxxx) - 67 (small one) Holley 600 (1850) - 65 Motorcraft 4300 (xxxx) - 61 (OWA4-S) Barry Grant 625 (xxxx) - 61 (Road Demon) Edelbrock 600 (1405) - 61 Carter AFB (4664) - 57 Motorcraft (4350) - 57 --------------- (4) MORE POSTS ON PAGE 2 -> BUT NOT ON WAYBACK MACHINE ! ------------------- -> ( 14 ) POSTS REPLIES ON PAGE 1 - SAVED HERE ALL post BY KEN PARKMAN ( 4 ) MORE POSTS ON PAGE 2 -> BUT CARP! I CAN'T FIND! NOT ON WAYBACK MACHINE ! -> Today, Wed, Feb 20, 2019 -> post on Billd Forum to Ken Parkman asking for missing text ----------------- crap ! PAGE 2 WAS not SAVED BY WAYBACK MACHINE ! And this is the image, hope it is legible, have yet to take time to type it up: Edited by PHAT69AMX - Feb/13/2020 at 9:59pm
	Link to a Short YouTube Burnout Video

javelinjason Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: May/20/2010 Location: Bangor, PA Status: Offline Points: 91	Post Options Post Reply Quote javelinjason Report Post Thanks(0) Quote Reply Posted: Feb/14/2020 at 7:45am
	This is all far and above my original question, but it has turned out to be a great discussion! If this were more of a performance build, I'm sure we would have went with a different CFM rated carburetor. Maybe for the next one!
	-1972 Javelin SST -1973 Javelin -1973 Javelin AMX PC

PHAT69AMX Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926	Post Options Post Reply Quote PHAT69AMX Report Post Thanks(0) Quote Reply Posted: Feb/14/2020 at 2:13pm
	It you just want a new bolt on carburetor that works - the Summit Brand Crabs people say are good. They are just a rebranded Holley design from the 80's, and are low cost. If you are ok with rebuilding and tuning a carb, get a used holley list 1850 for $50 off MarketPlace. Getting pieces and parts and 'input', ha, for the 1850 Holley will be easy. All also available for the MotorCraft AutoLite but less readily, maybe more costly, a new float for that is high dollar from what I understand, and the Dual Inlet Needle set-up can be tricky to get correctly set-up, some web sources show blocking off the 2nd Inlet Needle. For the Spacer, finding stock will be less than easy. Aftermarket carbs most likely will already have the needed hose connections that were in the stock spacer since the stock MotoCraft AutoLite lacked them. Square Flange 4-hole Carb Spacer of a material, brand, height, of your choice, some folks even make them out of wood at home.
	Link to a Short YouTube Burnout Video