What To Do About Carburetors

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I have a edelbrock 1405 (600 cfm) and a 351 cleveland in my car, so what I want to know is what was the original carb on my 71 mach 1 and if what I have on there at this point is appropriate to my engine.

 
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It will work fine. You can run a bigger carb, but as long as you arehappy with the performance, that one will give you easy tunability and decent mileage.
What would be the benefit of a bigger carb, of if i changed it out to a holley, a friend was telling me that a holley is what it would have rolled out to the factory with is that true, o and some thing about the gas pump having to to with the carb to, but did-int understand that part to well.

 

caspianwendell

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they came with several different carbs including motorcraft, and holly and for a standard factory built engine, a 650 or 700 cfm would be more fitting but as Jeff said if it runs good and you like it...don't change it. The benefit of the added cfm is just what it says more cubic feet per minute...this equals more HP and better throttle response off the line. The more fuel and air in the engine and better flow through the exhaust gives you more HP and torque at the wheel.

 
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It would have rolled out of the factory with an Autolite/motorcraftt spreadbore 4300 if it is a 4 BBl

Holleys are different, not necessarily better, but different than edelbrocks.

The fuel pump has nothing to do with the carburetor you use unless you use an aftermarket pump that operates at higher pressures.

The larger Holley would give you the ability to burn more fuel and make more horsepower. It is a balancing act, the bigger the carb, the harder it is to get good throttle response, and good idle. If your engine is otherwise stiock you could handle a 650CFM or maybe a 700 CFM carb, but there isn't enough difference to justify it.

Holleys are great, but they do require more effort to set up and tune. Edelbrocks have metering rods that can be replaced with the carb on the engine, for fine tuning that is much easier, they have no power valves to blow out either. I run a holley, but I have run the Edelbrock (Which BTW is an old Carter AFB design which was used on lots of muscle cars including fords up til 1971.

 

Don65Stang

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I can only add that a smaller bore size in the carb (lower cfm carb) gives better throttle response whereas a larger bore gives more top end hp. You have to truthfully answer the question to yourself how you drive the car. Do you floor it at every green light like at a drag strip with 5000, 6000 or 7000 rpm shift points? If so I recommend a 750 cfm carb.

My shift points are between 3000 & 5000 rpm for my fair weather driver. My highway rpm is 3000 to 3500. A 700 cfm would be more suited for my driving style.

Funny thing is that I drive my all weather driver, a VW golf, with almost the same shift points. It looses it's grunt at 5000 rpm due to intake restrictions and other things. It has great throttle response though.

 
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I have a edelbrock 1405 (600 cfm) and a 351 cleveland in my car, so what I want to know is what was the original carb on my 71 mach 1 and if what I have on there at this point is appropriate to my engine.
Man that's a loaded question, it's kind of liking asking what's the best color for my car. It all depends on how built your engine is and what your looking at doing with it. I ventured there earlier and received tons of well thought out responses based upon past experiences and expectations. Recommendations ranged from 550 to even 800 cfm. My conclusion after listening to everone was I was better off with to little cfm rather than to much. I was torn between getting a 650 or 700 cfm because I just want dependable "spirited" street performance, not interested in racing it. I went with the Edelbrock thunderseries 650 cmf and I'm happy with it. It ran perfectly right out of the box and more responsive than the Autolite 4300D I took off it. The Edelbrock for some reason turned out more heat sensitive than the Autolite so I had to had a heat sink under it.

 
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Hay thanks for the info I think we are looking for the same thing so im just going to go with the 600 it has in it dont think the extra 50 will make that much of a difference, and spend the cash some other place.

 

ramair

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I see your are in Colorado, you need to take elevation into consideration when picking a carb for a engine. The higher up you are, the thinner the air. I have a Holley 600cfm on my 351W in my 73 and it is more than enough here which is around 5200 ft elevation. I also had a 78 F250 that had an all stock 460 and an 600cfm carb. The original Motorcraft was junk and I put on a 600cfm Edelbrock carb. After the carb swap the truck ran like a dream and actually got 14-16 mpg with the Eddy carb. I miss that truck.:(

 
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