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Direct Link To This Post Topic: Carb info
    Posted: 10-October-2010 at 1:53PM
Carb thread started here for info to be used by all.
 
Here's the start...
 
Took it from this page...
Calulcating CFM

Volumetric Efficiency

Actual Air/Fuel Mixture Intake         = Volumetric Efficiency 
Theoretical Air/Fuel Mixture


Engine/Carburetor Sizing Relationship

The larger the engine, the more air it's capable of "gulping". In math terms, it looks like this:

  Cubic In. Displacement  

X     Maximum RPM   

=  Maximum CFM

2

              1728

An Example:

     289 Cubic Inches     

X         8000 RPM    = 669 CFM 

2

              1728

This is still not the final answer for sizing a carburetor. The volumetric efficiency must be taken ito consideration. 

In our example a 289 @ 8000 RPM can use 669 CFM
however
660 CFM x .90 volumetric efficiency = 602 CFM
669 CFM x .85 volumetric efficiency = 568 CFM

     Our example is based on a Hi-Po 289. Ford installed a 600 CFM Autolite 4100 on this engine. Did Ford engineers know what they were doing? You Bet!
     A standard "A" code or "D" code 289 4 barrel with the factory valve train will not run much above 6000 RPM.
     6000 RPM requires 501 CFM x .85 volumetric efficiency = 426 CFM. Ford installed a 480 CFM carburetor!

Bring on the info you have found.
I have a bunch of sites I have found looking for info on the dirt motor.
 
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Direct Link To This Post Posted: 10-October-2010 at 1:56PM
From the same site... you can see the venturi size casting on the side of the Ford Carb.
 
Carburetor Identification and Location of Engineering Numbers

Above is a picture of an Autolite 1100 for an Automatic Transmission vehicle. The 1100 for a manual transmission vehicle has only one diaphragm.

Above is a picture of a Holley 4 Barrel Carburetor. Please note the three lines of information on the air horn. The first line will be the Ford or GM part number, the second line will be the Holley List number and the third line will be the date code. For info on deciphering Holley date codes see the related FAQ.

 

Above (right) is a picture of the driver's side of an Autolite 4100. Please note the Ford engineering number stamped on the mounting flange (bottom circle). Above the engineering number, in raised characters, is the venturi size in a circular pattern (top circle). Above (left) is a picture of the driver's side of an Autolite 4300. Note that the Ford engineering number is also stamped on the mounting flange.

Above is a picture demonstrating the difference between a long accelerator pump snout and a short accelerator pump snout.

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Direct Link To This Post Posted: 10-October-2010 at 1:58PM

Well the shrunk pic if the one I was referring to. not a good pic.

you can see it on the website.
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Direct Link To This Post Posted: 19-October-2010 at 7:10PM
Originally posted by cowboyupdjcarl cowboyupdjcarl wrote:

Carb thread started here for info to be used by all.
 
Here's the start...
 
Took it from this page...
Calulcating CFM

Volumetric Efficiency

Actual Air/Fuel Mixture Intake         = Volumetric Efficiency 
Theoretical Air/Fuel Mixture


Engine/Carburetor Sizing Relationship

The larger the engine, the more air it's capable of "gulping". In math terms, it looks like this:

  Cubic In. Displacement  

X     Maximum RPM   

=  Maximum CFM

2

              1728

An Example:

     289 Cubic Inches     

X         8000 RPM    = 669 CFM 

2

              1728

This is still not the final answer for sizing a carburetor. The volumetric efficiency must be taken ito consideration. 

In our example a 289 @ 8000 RPM can use 669 CFM
however
660 CFM x .90 volumetric efficiency = 602 CFM
669 CFM x .85 volumetric efficiency = 568 CFM

     Our example is based on a Hi-Po 289. Ford installed a 600 CFM Autolite 4100 on this engine. Did Ford engineers know what they were doing? You Bet!
     A standard "A" code or "D" code 289 4 barrel with the factory valve train will not run much above 6000 RPM.
     6000 RPM requires 501 CFM x .85 volumetric efficiency = 426 CFM. Ford installed a 480 CFM carburetor!

Bring on the info you have found.
I have a bunch of sites I have found looking for info on the dirt motor.
 


That would mean that the 521 I ordered would require (at an assumption of .85 volumetric efficiency) over 700CFM of carb. That would mean that a 750 CFM carb would be the absolute minimum you could stick on the motor.

Wow!
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Direct Link To This Post Posted: 27-October-2010 at 5:53PM
I ran my numbers through it...
 
347 cu in/2 = 173.5
 
6000 rpm/1728 = 3.472
 
173.5 x 3.472 =  602.39 CFM
 
602.39 cfm x .90 efficiency = 542 CFM
 
so it looks like a good 600CFM carb is the way to go!
MAYBE a 650 jetted way down to stay clean and lean!?
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Direct Link To This Post Posted: 28-October-2010 at 3:31AM
Everything I have read in the last many years always told me to run a 600cfm carb on any 302 based motor. I bought my brothers 700cfm double pumper but am deciding to stick with my 600 universal instead. The only way I know of to get away with a bigger cfm and/or a dp carb it to use a stick behind it and you will be ok. I used a 650dp on my 85 GT that was stock with only the outside bolt ons and .030 off the heads and that thing flew. I tried a 650dp on my built .060 over 302 in my Ranchero and it was a dog until I went back to the 600 universal. Just my expierence with the bigger vs smaller carb. Wink
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Direct Link To This Post Posted: 29-October-2010 at 6:40AM
Originally posted by cowboyupdjcarl cowboyupdjcarl wrote:

I ran my numbers through it...
so it looks like a good 600CFM carb is the way to go!
MAYBE a 650 jetted way down to stay clean and lean!?
 
common misconception, a larger than needed venturi will realize reduced airspeed for a given engine rpm or poor 'carb signal', resulting in a lean A/F mixture
 
oversized carbs usually require more jet to maintain correct AFR, increased duration / overlap cams contribute to poor carb signal
 
a slightly oversized carb will show performance improvements in the mid>high rpm power ranges, sacraficing low end response. how much sacrafice vs how much gain is the balancing act. linkage ratios and venturi sizes(squarebore vs spreadbore) can also be used to negate low end losses, a spreadbore 750 with a late acting secondary linkage can maintain or improve stock low end driveability over a much smaller overall cfm squarebore carb with larger primaries Wink
 
as mentioned above, the rest of the combo plays a role too. tall highway gears and stock torque converters don't play well with oversized carbs. manual trans, high stall converters and low gears are much more forgiving to big primary venturis


Edited by Rockatansky - 29-October-2010 at 6:47AM
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Direct Link To This Post Posted: 29-October-2010 at 1:47PM
I was thinking a 650 with LATE coming on secondaries cam or a STIFF spring to make sure the secondaries only come on when I REALLY want them to!
 
Plenty of volume in the primary to run all over the country with the secondaries there ONLY when I NEED/WANT them!
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Direct Link To This Post Posted: 29-October-2010 at 2:12PM
maybe a vacuum secondary with a Quickfuel adjustable housing to get your opening point where you want it
 
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Direct Link To This Post Posted: 29-October-2010 at 2:44PM
Love the above part! May have to look into that. I also forgot to mention with the vehicles I listed above the 85 GT was a stick with 3.42 gears and the Ranchero was a 2K stall C-4 with 4.11 gears. The Ranchero motor was a Mexican 302 that was .060 over decked .030 and had GT40P heads milled .030. I had a Comp 262H with .498 lift. As stated I started with a 650DP mech. sec., Weiand Xcellerator single plane, and 1.7 ratio roller rockers. This combo fell off at 5500 rpm for some crazy reason. I couldnt spin any higher or it would just suck. The first thing I changed was the rockers back to stock 1.6 and it made an improvement. I then switched to the 600 vac. sec. and found an even better improvement. The last and biggest improvement I have ever made in my life was swapping the single plane Weiand for a Performer RPM air gap intake. That was the best part as I now had strong power all the way up to 6500 rpm! Yeah that really woke the truck up. Combo is a key part to making power.
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Direct Link To This Post Posted: 09-December-2010 at 7:17AM
Carb question.
 
What is the linkage on the side of the carb for an AOD tranny?
Is it the same linkage already on the car for the kickdown rod?
SAME or DIFFERENT?
 
I have a line on a Ford/Holley 600cfm 4bbl that came off an AUTO tranny truck but the guy does not know if it was from an AOD, C6, C4, etc...
 
WILL it work on the AOD?
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Direct Link To This Post Posted: 09-December-2010 at 7:21AM
i wonder if the kickdown helps a lot, it was never hooked up on mine
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Direct Link To This Post Posted: 09-December-2010 at 7:35AM
well, the standard Holley warning is that AOD is not compatible, so i'm gonna go with different. Lokar makes both a kickdown and an AOD linkage bracket, i've read that one of them works better for the other but i don't remember which way that is
 
KDP-20C4HT     Polished Hi-Tech Ford C-4 Kickdown Kit
KDP-20C6HT     Polished Hi-Tech Ford C-6 Kickdown Kit
KDP-2FMXHT    Polished Hi-Tech Ford FMX Kickdown Kit
KDP-2AODHT    Polished Hi-Tech Ford AOD Kickdown Kit

i don't like that Lokar calls the AOD a kickdown, it's throttle pressure
 
yes ilyes, the kickdown makes a BIG difference in driveability


Edited by Rockatansky - 09-December-2010 at 7:45AM
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Direct Link To This Post Posted: 10-December-2010 at 2:56PM
Here is the page showing the 2BBL venturi size compares to the CFM flow.
 
 
 
Venturi size
CFM
Flange
1.01

240

1.02
245
1.08
287
1.14
300
1.21
350
1.23
351
1.33
424
 
So check it out.
 
Ford used the 1.08 on almost everything!
a 1.23 was one they used on the 351 in a truck.
seen 1.14 on 302 truck motors
1.21 on the 351 cars like the Torinos
the 1.33 which is the holy grail of Ford 2BBL carbs was what they put on the 429 2BBL cars.
 
So do the math...
 
347 cu in/2 = 173.5
6000 rpm/1728 = 3.472
173.5 x 3.472 =  602.39 CFM
602.39 cfm x .90 efficiency = 542 CFM
NO Ford 2BBLs are enough to run it right!
 
302 cu in/2 = 151
6000 rpm/1728 = 3.472
151 x 3.472 =  524 CFM
524 cfm x .90 efficiency = 471.6 CFM
524 cfm x .80 efficiency = 419.2 CFM
 
So HOW does Ford see 287CFM as a good fit for a ANY 302!?
Even if I used a 1.23 carb from a truck 351 it is still WAY UNDER CARBED!!!
 
So in order to make a Ford anysize run efficient with power you HAVE to run a small 4BBL or a Holley 500cfm 2BBL. Rochester makes a 500cfm 2bbl they used on big GM products IF you can find one of them!
 
 
 


Edited by cowboyupdjcarl - 10-December-2010 at 3:09PM
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Direct Link To This Post Posted: 10-December-2010 at 3:12PM
I don't think Ford intended your stock motor to be run at 6000 rpm. Not that is cannot do 6000 rpm, but their intention was to make a really "driveable" car, and sacrifice performance. 
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Direct Link To This Post Posted: 10-December-2010 at 3:33PM
LOST THE POST!
 
Well let's see IF Ford figure it at 2500 for optimal efficiency at highway speed...
 
302 cu in/2 = 151
2500 rpm/1728 = 1.447
151 x 1.447 =  218.5 CFM
218.5 cfm x .90 efficiency = 196.65 CFM
218.5 cfm x .80 efficiency = 174.8 CFM
 
 
well I guess that about figures it out!
1.08 Venturi is 287 CFM
 
302 cu in/2 = 151
4500 rpm/1728 = 2.604
151 x 2.604 =  393.23 CFM
393.23 cfm x .90 efficiency = 353.9 CFM
393.23 cfm x .80 efficiency = 314.6 CFM
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Direct Link To This Post Posted: 10-December-2010 at 3:34PM
So either Ford was saying 4000rpm was max or the engine was running 70% efficiency.
 
THAT IS SAD!
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Direct Link To This Post Posted: 10-December-2010 at 3:54PM
More inducement for performance minded folks to buy 4V cars and get additional options (hence more $$$ per car sale)?
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Direct Link To This Post Posted: 10-December-2010 at 9:02PM
4bbls and 2bbls are not rated by the same measure,
to make it even worse, each manufacturer uses their own standard
 
 


Edited by Rockatansky - 10-December-2010 at 9:07PM
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Direct Link To This Post Posted: 24-December-2010 at 2:00PM
What do y'all think about a Holley 450CFM 4bbl or Edelbrock 500cfm 4bbl carb?
 
Why do I ask?
Looking at the 2bbl numbers...
302 cu in/2 = 151
6000 rpm/1728 = 3.472
151 x 3.472 =  524 CFM
524 cfm x .90 efficiency = 471.6 CFM
524 cfm x .80 efficiency = 419.2 CFM
 
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