Carb for 429 SCJ

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1971 Ford Mustang Mach 1, 429 Super Cobra Jet, 4.11, Detroit Locker
When I put together my 1971 Mach 1, 429 SCJ, I used a Holley 750 CFM rather than the factory original Holley 780--could not find one. 

Has anyone with a 429 SCJ had success (consistency, dependable, long-lasting) with any other carb, one equal to the Holley 780? 

Thanks. 

Mach 1 1971 429 SCJ.jpg

 
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1971 J Code Mach 1
1972 H Code Mach 1
Tim-

First off, your car is beautiful!

What are you looking for out primarily, performance, driveability?

Generally a vacuum secondary carb will drive more smoothly but a mechanical secondary will probably make more power. A smaller carb will have better throttle response and transition while increasing the cfm will make more power in the upper rpms. 

How stock is your engine? If you are more interested in performance then I think a larger carb than the stock 780 is probably a better choice especially if you still have drag pack gears. 

I am partial to Holley-style carbs, but that’s just because I’ve more experience with them, but I’m far from an expert tuner. I found a nice used 950 HP locally and sent it off to Pro Systems to have it setup to my particular combination. I haven’t put many miles on my car with it but it seems to work pretty well. My 460 is an old crate engine, 10.5:1, FRPP SCJ heads, Stealth intake, large-ish hydraulic cam, headers and 3.91’s out back.

 
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1971 Mustang Mach 1 M code 351 4 speed
That 750 CFM vacuum carb should work perfectly on your 429 SCJ. That carb looks like a 0-3310. The only major difference between it and the factory 780 would be that the 780 used a rear metering block instead of the metering plate that is used on the carb you currently have. Holley sells a metering plate kit for the back if you want to change that. There is no reason why your 429 should not run as well with that 750 as it did with the OEM 780. The 30 CFM difference should not be enough to make much if any difference. Are you having any issues with how the car runs with that 750? If it is not running well, it probably just needs some adjustment.

 
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One thing that I recall from my days of doing Holley carbs is that the 750 and the 780 carbs were basically the same. If you look at the specs, the venturii diameters and the throttle blade diameters are identical, so they should flow exactly the same, but they are rated differently. The difference in the CFM rating is due to the boosters. The 750 CFM carbs use the straight boosters and the 780 CFM, like the 0-4628, uses the down leg booster. The straight booster is a little more restrictive and that is where you loose the 30 CFM. The first 0-3310 carbs were rated at 780 CFM as they used the down leg booster, they later changed to the straight leg booster and dropped the rating to 750 CFM. Here are some specs you can look at:

https://documents.holley.com/techlibrary_carb_numerical_listing.pdf

 
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Joined
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1971 Ford Mustang Mach 1, 429 Super Cobra Jet, 4.11, Detroit Locker
One thing that I recall from my days of doing Holley carbs is that the 750 and the 780 carbs were basically the same. If you look at the specs, the venturii diameters and the throttle blade diameters are identical, so they should flow exactly the same, but they are rated differently. The difference in the CFM rating is due to the boosters. The 750 CFM carbs use the straight boosters and the 780 CFM, like the 0-4628, uses the down leg booster. The straight booster is a little more restrictive and that is where you loose the 30 CFM. The first 0-3310 carbs were rated at 780 CFM as they used the down leg booster, they later changed to the straight leg booster and dropped the rating to 750 CFM. Here are some specs you can look at:

https://documents.holley.com/techlibrary_carb_numerical_listing.pdf
Hey Matt:

Thank you for your posts in reply to my carb question. They were helpful.

You have pretty much settled the issue in my mind regarding the Holley 750. 

It's what I needed to hear.

Many thanks, Tim

 

Rusty Relic

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New Zealand
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71 mach 1 SCJ
69 mach 1
67 convertible
When I put together my 1971 Mach 1, 429 SCJ, I used a Holley 750 CFM rather than the factory original Holley 780--could not find one.

Has anyone with a 429 SCJ had success (consistency, dependable, long-lasting) with any other carb, one equal to the Holley 780?

Thanks.

View attachment 56514
Hi Ponypastor
I have just fitted a 750 Holley and definitely no issues with performance.One hint ,Reverse the fuel bowl feed pipe and bring your fuel line around the back of the carb. SCJ.jpg I did this because the original 780 had the fuel feed on the drivers side and using a 750 with fuel feed on passengers side has issues with fuel line routing past the top radiator hose.
 

Rusty Relic

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69 mach 1
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Be carful with the heat. If you are getting vapor lock in the hotter weather then you may have to re route to the front. I tried it that way and had problems.
Thanks John , I will keep an eye on that but so far so good down here in New Zealand(y)
 
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Hi Ponypastor
I have just fitted a 750 Holley and definitely no issues with performance.One hint ,Reverse the fuel bowl feed pipe and bring your fuel line around the back of the carb. View attachment 62734 I did this because the original 780 had the fuel feed on the drivers side and using a 750 with fuel feed on passengers side has issues with fuel line routing past the top radiator hose.
I used stock fuel pump, cut stock stainless line, added an Earls fuel filter and bent up some stainless tubing to clean it up.
 

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JJU9507

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corona ca
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1971 mach 1 auto, 507 bbf, alum heads ect.
Hi Ponypastor
I have just fitted a 750 Holley and definitely no issues with performance.One hint ,Reverse the fuel bowl feed pipe and bring your fuel line around the back of the carb. View attachment 62734 I did this because the original 780 had the fuel feed on the drivers side and using a 750 with fuel feed on passengers side has issues with fuel line routing past the top radiator hose.
I WANT those valve covers!! Are they blue thunder?
 
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