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Replacement carb for stock 351C


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Hi,

I have the stock motorcraft 4bbl on my Q-code 72 4 speed. After 45 years of use I want to put a new carb for better drivability. What is the easiest replacement carb with the stock intake. Seems that people like the Holley 4150 with electric choke. I'm looking for ease of install and drivability-it's racing days are over! Thank you

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I have used Holley's Street Avenger carbs in the past, I think the 670 cfm version would fit the bill nicely. They have a lot of features over the base, universal carbs.

 

Stupid question that I should know the answer to: is the OEM Q-code carb a square bore?

Matt

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I have used Holley's Street Avenger carbs in the past, I think the 670 cfm version would fit the bill nicely. They have a lot of features over the base, universal carbs.

 

Stupid question that I should know the answer to: is the OEM Q-code carb a square bore?

 

It's sort of like a mini spread bore-not like a Q-jet or Thermoquad but the secondaries are slightly larger than the primaries and that is why the fitment is so important

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I have used Holley's Street Avenger carbs in the past, I think the 670 cfm version would fit the bill nicely. They have a lot of features over the base, universal carbs.

 

Stupid question that I should know the answer to: is the OEM Q-code carb a square bore?

 

It's sort of like a mini spread bore-not like a Q-jet or Thermoquad but the secondaries are slightly larger than the primaries and that is why the fitment is so important

This adapter may work, I'm not 100% certain. http://www.tdperformance.com/site/?d=108&dt=108&callHandle=productList&start=15&limit=5

 

I feel this is the most bang for the buck right now for a street carb. http://www.summitracing.com/parts/qft-sl-750-vs/overview/

The level of adjustability at that price is impressive. Chuck

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I'm using a 625cfm Street Demon carb. So far, wonderful drivability, and SUPER-EASY, instant tuning . Maybe there's a little more power to be gained with other carbs, but this thing was inexpensive and - did I mention -EASY! Swapped the carb and had it tuned in less than an hour. I did use an Edelbrock 8725 spacer so the butterflies would fully open.

 

However, I can't speak to long term reliability as I've only had it a short time.

 

http://www.demoncarbs.com/1900.asp

1973 Mach 1 Q-code C6 3:50

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I'm using a 625cfm Street Demon carb. So far, wonderful drivability, and SUPER-EASY, instant tuning . Maybe there's a little more power to be gained with other carbs, but this thing was inexpensive and - did I mention -EASY! Swapped the carb and had it tuned in less than an hour. I did use an Edelbrock 8725 spacer so the butterflies would fully open.

 

However, I can't speak to long term reliability as I've only had it a short time.

 

http://www.demoncarbs.com/1900.asp

 

That's the carb I've been looking at. Lots of good reviews. Sent you a PM.

73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

082-hot-rod-power-tour-2017-1970-1970s.jpg

 

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I prefer the most proven and simple carbs around, which are the Holley and Quick Fuels, and the Quick Fuels were designed by Holley engineers.

 

Also, these carbs have easily adjustable secondaries, and you can often increase performance by installing a lighter secondary spring . As far as I know, that Demon does not have adjustable secondaries . If not, you are giving up a huge tuning option.

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I prefer the most proven and simple carbs around, which are the Holley and Quick Fuels, and the Quick Fuels were designed by Holley engineers.

 

Also, these carbs have easily adjustable secondaries, and you can often increase performance by installing a lighter secondary spring . As far as I know, that Demon does not have adjustable secondaries . If not, you are giving up a huge tuning option.

 

Barnett,

I have not gotten that far in investigating these carbs but they are not the old demon carbs, it is a new design with slightly smaller primaries to improve throttle response. I would be curious to hear what you think of these in particular. Here is a link..

 

http://www.demoncarbs.com/Types/Street%20Demon.asp

73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

082-hot-rod-power-tour-2017-1970-1970s.jpg

 

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I prefer the most proven and simple carbs around, which are the Holley and Quick Fuels, and the Quick Fuels were designed by Holley engineers.

 

Also, these carbs have easily adjustable secondaries, and you can often increase performance by installing a lighter secondary spring . As far as I know, that Demon does not have adjustable secondaries . If not, you are giving up a huge tuning option.

 

Barnett,

I have not gotten that far in investigating these carbs but they are not the old demon carbs, it is a new design with slightly smaller primaries to improve throttle response. I would be curious to hear what you think of these in particular. Here is a link..

 

http://www.demoncarbs.com/Types/Street%20Demon.asp

 

I took another look at it and it does have adjustable secondaries . The primary venturis are a hydrid and work similar to an annular which improves throttle response and increases power and therefore increases mileage.

 

The boosters have just as much to do with good throttle response as the small primary venturis, but keep in mind that as soon as you open the secondaries, all the throttle response provided by small primaries is gone.

 

If you got a carb that had annular boosters and throttle plates that were the same size front and back instead of staggered sizes, the throttle response would be similar to the Demon, and any difference would be so small that it would be difficult to notice.

 

What these types of carburetors do on some setups is cause a slight bog or hesitation when the secondaries open which can be hard to tune out . This is due to the huge difference between the size of the very small front venturis vs the massive size of the secondaries.

 

These carbs that have the fuel controlled by needles typically get a little better mileage if they are properly tuned and this type of car that also has annular boosters will get even better mileage.

 

All in all, imo, it's a good carb for a low performance engine that doesn't get driven hard often which is not a bad thing, but it's not the best choice for a high perf engine.

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Thanks for your insite. My H code is currently mostly (i.e. The heads have never been off the car) stock with the exception of long tube headers and a Pertronix 3 ignition.

73 Grande H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

 

- Jason

 

 

082-hot-rod-power-tour-2017-1970-1970s.jpg

 

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I'm running an old 66 Shelby (Holley 715 CFM with central pivot floats and Lemans bowls) vacuum secondary's. It's a great carb but VERY expensive and hard to find. I put a spacer for a Boss 302 with a port for the PCV because as you know the PCV on the 4300D is ported out of the body of the carb. This set up works fine but if I were doing it over today I'd change the manifold and run a modern 600 CFM Holley.

Going fast is fun but life is short so slow down and enjoy the ride :D Frank

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