Hello, I heard about that the demon carbs are a Little bit smaler as the holley´s .
So my question is :
Is a 750 Demon a good carb for a stock 351 C with doae closed chamber heads ?
Thanks
Peter
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From what I understand, the 650 should be good for 400 HP applications. 750 may be a bit too much....
why do you have one?
why do you have one?
Before replacing the OEM carb and manifold I researched replacement carbs. I was told by several knowledgeable people that the Demons were flow rated somewhat differently than the Holly they were patterned after. A 650 Demon flowed comparable to a 750 rated Holly. Matched to an Edelbrock Performer I opted for the 650 Speed Demon with vac sec. & electric choke. After many years I am very satisfied when the performance and reliability.
Holley’s measurement technique is well known; they test their model 4150 four barrel carburetors dry at a depression of 1.5 inches of mercury. Information regarding the measurement technique of other manufacturers is often not stated. The Holley “clone” carburetors manufactured by Quick Fuel Technology (QFT) and Demon Carburetors employ the same depression as Holley, however Demon Carburetors chose to measure their carburetors wet in their earlier years, although that practice seemed to have been abandoned at some point.
Since all carburetor manufacturers do not use the same criteria as Holley for determining their carburetors air flow capabilities comparison of carburetors manufactured by different manufacturers can be imprecise. When I am in doubt of a rating I compare the diameter of the throttle blades and the inside diameter of the venturi throats of the carbs I am comparing.
The Q code and R code versions of the 351C were equipped from the factory with a 750 cfm Motorcraft model 4300D spread bore carburetor. I have found over the years that a carburetor rated 735/750/780 cfm (dry flowed at 1.5" Hg depression) to be an excellent street carb for the 351C with 4V heads and a dual plane intake manifold. This is a 4 barrel carburetor with 1-11/16" throttle blades and 1-3/8" venturi throats. This size is a bit of a compromise, a 650 cfm carb would be the best low rpm carb, an 850 cfm carb is a better high rpm carb. The 750 allows the engine to rev higher and faster than a 650 without hurting drivability, but its not quite as good at high rpm as an 850. The bigger carburetors will allow the engine to operate at higher volumetric efficiency because for any given amount of air flow the intake manifold vacuum shall be less.
The whole reasoning behind a dual plane intake manifold is increasing mid-rpm power. However, a 650 cfm carb mounted on a single plane Edelbrock Torker manifold is a good street induction system too.
Selecting a carburetor equipped with annular booster venturis is worth your consideration too. They improve venturi signal at low rpm and atomize the fuel better. They accomplish the same thing as the small primaries of a spread bore carburetor (i.e. improve low rpm drivability) plus they allow the engine to make more power throughout the engine's operating range.
Since all carburetor manufacturers do not use the same criteria as Holley for determining their carburetors air flow capabilities comparison of carburetors manufactured by different manufacturers can be imprecise. When I am in doubt of a rating I compare the diameter of the throttle blades and the inside diameter of the venturi throats of the carbs I am comparing.
The Q code and R code versions of the 351C were equipped from the factory with a 750 cfm Motorcraft model 4300D spread bore carburetor. I have found over the years that a carburetor rated 735/750/780 cfm (dry flowed at 1.5" Hg depression) to be an excellent street carb for the 351C with 4V heads and a dual plane intake manifold. This is a 4 barrel carburetor with 1-11/16" throttle blades and 1-3/8" venturi throats. This size is a bit of a compromise, a 650 cfm carb would be the best low rpm carb, an 850 cfm carb is a better high rpm carb. The 750 allows the engine to rev higher and faster than a 650 without hurting drivability, but its not quite as good at high rpm as an 850. The bigger carburetors will allow the engine to operate at higher volumetric efficiency because for any given amount of air flow the intake manifold vacuum shall be less.
The whole reasoning behind a dual plane intake manifold is increasing mid-rpm power. However, a 650 cfm carb mounted on a single plane Edelbrock Torker manifold is a good street induction system too.
Selecting a carburetor equipped with annular booster venturis is worth your consideration too. They improve venturi signal at low rpm and atomize the fuel better. They accomplish the same thing as the small primaries of a spread bore carburetor (i.e. improve low rpm drivability) plus they allow the engine to make more power throughout the engine's operating range.
Thanks for helping me. When I look to the Hall manifold and the 48ida Webers so every carb looks verry small for me.
Some people say that they run a 1050 carb on the 351C
with standart Boss heads.
Can this be true?
When a carb is to big, what does the engine do than?
Only a to high co2 Level wich can not droped down at idle rpm?
Are the 48ida Webers a good solution for the engine?
If yes : do I realy get more HP with the Webers?
Or is the system only for the optical view?
Thanks a lot
Some people say that they run a 1050 carb on the 351C
with standart Boss heads.
Can this be true?
When a carb is to big, what does the engine do than?
Only a to high co2 Level wich can not droped down at idle rpm?
Are the 48ida Webers a good solution for the engine?
If yes : do I realy get more HP with the Webers?
Or is the system only for the optical view?
Thanks a lot
I believe that MOST Weber users would freely admit that the "look" of the Webers is NOT worth the cost nor the myriad of idiosyncrasies associated with the Webers.
Difficult to improve upon the HP & reliabilities of a properly jetted & tuned Modern 4 barrel carburetor...Mark
Difficult to improve upon the HP & reliabilities of a properly jetted & tuned Modern 4 barrel carburetor...Mark