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Discussion Starter #1
69 Fastback with a 4 spd toploader & 9" rear.

1968 289 block with the 302 stamp

bored 60 over (yes it's still doing good)


1965 heads C5AE 65. milled 1/8th

Compcam # 31-226-3, Grind # 280H
Valve lift 512

Intake Holley Street Dominator 12152 single plane
Holley 3310-6 dual feed 750 vac sec.

I want to change induction to a Edelbrock F4B dual plane and a holley 650 Vac sec.

Prior induction I think is too big and a waste.

What carb & intake would be best.
Thanks to all in advance.
John
 

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I have a late model 5.0 and run a 570cfm street avenger, works fantastic.
 

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69 Fastback with a 4 spd toploader & 9" rear.

1968 289 block with the 302 stamp

bored 60 over (yes it's still doing good)


1965 heads C5AE 65. milled 1/8th

Compcam # 31-226-3, Grind # 280H
Valve lift 512

Intake Holley Street Dominator 12152 single plane
Holley 3310-6 dual feed 750 vac sec.

I want to change induction to a Edelbrock F4B dual plane and a holley 650 Vac sec.

Prior induction I think is too big and a waste.

What carb & intake would be best.
Thanks to all in advance.
John
Actually, something in the 600 CFM range that has been custom tuned to get an AFR of 14.5 @ idle and 13, or so, at WOT. The operative word is "custom" tuned. This being stated, use a vac gauge to tune your new carb. The dual plane for a street warrior is an excellent choice. My junk in one of it's previous builds, ran a 600 Eddy and made 348 RWHP. It was tuned for the engine's configuration.
Happy Motoring!
 

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Discussion Starter #4
Thank you for your replys!
So far it looks like a dual plane and a 600cfm.
Any other suggestions
 

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Discussion Starter #5
In regards to the 600cfm.
What model Holley # would fit. I would like to get a used one and rebuild it. I wonder if it will fit on top of the Edelbrock F4B intake???

I also see the edelbrock performer might be a good choice and it should mate to the F4B Intake.
I appreciate your response.
 

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750 cfm carb is too much for that motor. 600-650cfm is much better. With a 4 speed you could probably get away with a double pumper if it's set up properly. But a vacuum secondary carb would be more user friendly for most people. I prefer Holley carbs for a variety of reasons, but nothing wrong with Edelbrock carbs. Edelbrock carbs are based on the old Carter AFB design.
 

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The F4B is a great intake BUT the carb pad is so small it has trouble sealing to a lot of carbs. Run a phenolic spacer if you have the clearance. Otherwise get the 3/8" thick Edelbrock spacer part #9266 ($20 from Summit). Basically a thick gasket.
 

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67 coupe, 69 Sportsroof, 86 hatchback
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Personally I'd drop on back to around 500cfm. An autolite 4100 480cfm is a dead-on perfect match for a 302 if you want to go retro. An Edelbrock 500cfm is nice (I'm running one). People are always putting too big of a carburetor on street driven cars. One that is more properly sized makes a car a lot more fun to drive with the snappier low-end throttle response.
 

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Personally I'd drop on back to around 500cfm. An autolite 4100 480cfm is a dead-on perfect match for a 302 if you want to go retro. An Edelbrock 500cfm is nice (I'm running one). People are always putting too big of a carburetor on street driven cars. One that is more properly sized makes a car a lot more fun to drive with the snappier low-end throttle response.
+1, bigger is not better when it comes to carbs. A carb is designed and optimized for a particular air flow.

Think of it as wearing a pair of shorts in a track meet. Too tight and it constricts the blood and other things like your junk. Too loose, like some of todays long baggy shorts, and they are dragging around your ankles as you try to sprint down the track with one hand holding them up. If you were bigger (breathing more air) you would fill them out better. Same thing with a carb.

Dave (I'm a runner...could not resist the analogy.)
 

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Personally I'd drop on back to around 500cfm.

For a stock motor I'd say you're right on the mark. But he's running a decent mild cam with some compression and a 4 speed. I'm guess he's moving a bit more air than a stock motor.
 

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OK. Let's assume a redline of 6500 (being generous). An engine like most of us build will be at 85% volumetric efficiency or so. Run it through any number of free online calculators out there and you come up with 483cfm. Everbody uses the same basic calculator, even Holley. This isn't just me talking here, it's a formula based on physics.
If you assume full race 100% VE, then 568 cfm. The dynos tend to say the vast majority of "race" built n/a old school V8's actually are normally between 90-5% VE. An older bone stocker might be more like around 75%.
 

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I prefer Holley carbs for a variety of reasons, but nothing wrong with Edelbrock carbs. Edelbrock carbs are based on the old Carter AFB design.
? The basic Holley as we know it came out in what, 57? The AFB in the early 60's. The Edelbrock has annular boosters that offer better signal strength and atomizes the fuel better although at a penalty at WOT with more restriction. It also has an easily adjustable cruise circuit. I don't see anything wrong with the "old" Carter AFB design. It looks to me that the Carter /Edelbrock is a newer design of the two.

Nothing wrong with a Holley and there's nothing wrong with an Edelbrock.
 

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Heads were milled down 1/8"? Did your intake require milling to get the ports to match up?
 

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Free online carb cfm calculators are worth what you pay for them. What depression are these calculators set for? What happens when the depression changes; do you need more cfm? Do you really want to run a carb that only flows what you absolutely need? The idea behind making power is less restriction. Obviously there has to be a compromise here but the venturi size and booster design is what is really important.
 

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What depression are these calculators set for?
I presume you mean compression? Compression has nother to do with CFM. Compression takes place after the CFM are in the cylinder and the intake valve is closed.

The carb works because a low pressure inside the carb pulls fuel into the moving air stream. You have to remember that the operation of a carb is a total compromise. If you ran one RPM and the same load all the time, you could get a perfect setup in terms of air to fule ratio. The carb is sized to give you the best overall performance over the full speed range. You start playing with the carb size (pressure drop going thru the carb) now you have to adjust the jets to get a compromise on the air to fuel ratio and you move away from the best overall performance.

Why is there an idle circuit? It's another compromise to getting a carb where it will work over a wide range of speeds or more specific term...CFMs.

Also, why do you think all the CFM calculators are the same...it's because it's a very basic calculation.

In the end it's what ever works for you. However, I'm with Gypsy on this one.

Dave
 

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I presume you mean compression? Compression has nother to do with CFM. Compression takes place after the CFM are in the cylinder and the intake valve is closed.

The carb works because a low pressure inside the carb pulls fuel into the moving air stream. You have to remember that the operation of a carb is a total compromise. If you ran one RPM and the same load all the time, you could get a perfect setup in terms of air to fule ratio. The carb is sized to give you the best overall performance over the full speed range. You start playing with the carb size (pressure drop going thru the carb) now you have to adjust the jets to get a compromise on the air to fuel ratio and you move away from the best overall performance.

Why is there an idle circuit? It's another compromise to getting a carb where it will work over a wide range of speeds or more specific term...CFMs.

Also, why do you think all the CFM calculators are the same...it's because it's a very basic calculation.

In the end it's what ever works for you. However, I'm with Gypsy on this one.

Dave
Not compression, depression. Depression is basically another way of saying vacuum. Carb CFM are measured at a specific depression . 2V carbs are usually rated at a higher depression then a 4V carb. If you used the same 2V test method f on a 4V, it would have a higher CFM rating.
 

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Nothing wrong with a Holley and there's nothing wrong with an Edelbrock.

Hence my statement that Edelbrock carbs are fine. Many of the younger crowd are not aware of the origins of the Edelbrock carb and that was why I mentioned where it came from. I had a Carter AFB on a 65 Polara with a 383. Great running carb and was a snap to rebuild.
 

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I presume you mean compression? Compression has nother to do with CFM. Compression takes place after the CFM are in the cylinder and the intake valve is closed.

The carb works because a low pressure inside the carb pulls fuel into the moving air stream. You have to remember that the operation of a carb is a total compromise. If you ran one RPM and the same load all the time, you could get a perfect setup in terms of air to fule ratio. The carb is sized to give you the best overall performance over the full speed range. You start playing with the carb size (pressure drop going thru the carb) now you have to adjust the jets to get a compromise on the air to fuel ratio and you move away from the best overall performance.

Why is there an idle circuit? It's another compromise to getting a carb where it will work over a wide range of speeds or more specific term...CFMs.

Also, why do you think all the CFM calculators are the same...it's because it's a very basic calculation.

In the end it's what ever works for you. However, I'm with Gypsy on this one.

Dave
No, I meant depression. I'm pretty sure I know what compression is.
 

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I just wanted to throw this out there. Last years Engine Masters Champion was John Kaase with a 403 cubic inch Cleveland stroker motor. The engine made 677hp at 6,400 rpms. The engine was topped with not one, but two 1250 cfm Holley Dominators. Thats 2500 cfm of airflow through the carburetors. If you use the traditional carb cfm calculator and figure for 100% volumetric efficiency, the calculator says the engine only needs 816 cfm of airflow. Does that mean that he should have only put a Holley 850 double pumper on the engine??? I understand that 99% of people on this forum dont have an engine built anything like this engine here but the principles remain the same. You want to lower the restriction of airflow through the engine to make it more efficient. Once again its the venturi size that is important to keeping an engine streetable when talking about carburetor selection. This is why carburetors like the Holley HP series are so popular. You get increased airflow over other carbs that have the same size venturi's due to the lack of restriction at the air inlet into the carb with the removal of the choke horn and shape of the air inlet.
 

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Somebody asking about racing engines in this thread? I must have missed that. On the street you want airflow velocity and good fuel atomization, particularly at low RPM's. This makes for a street car that is reasonably economical, very responsive, and a blast to drive all around (within usual legal limits).
Now if the cops make a habit of waiting for you to leave the house on weekends because you like to "warm up" your tires on the way to the dragstrip you have a whole different set of requirements and are probably posting in the wrong section of the forum. And whatever is on that car has zero to do with what the original poster is asking. He's already of the fairly informed opinion that what his engine has is overkill for his purposes though it probably would be great for the strip.
I met one of the Holley support techs when I lived outside of Bowling Green years ago. In the conversation he mentioned how sick he was of tech calls from people with very ill behaved carbs because they bought an oversized "race" carburetor for their relatively mild street car. He had to keep telling people, "It doesn't work right because you BOUGHT THE WRONG ONE!" He was a bit stressed out and obviously venting and yelling at customers was not allowed if he wanted to keep his job. Poor guy. Knew a heck of a lot about carbs though.
 
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