Carb Recommendations for a 1974 Big Block please.
Thread Starter
Instructor
Joined: Apr 2001
Posts: 174
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From: Flower Mound TX
Carb Recommendations for a 1974 Big Block please.
I think it is time for a carb change. I would like something with more performance and obviously reliability. Demon Carb??
I have a 1974 Big Block.
Also I do not mind a used or reman if anyone wants to sell one.
Thanks for the help folks!
Texxas
:flag
I have a 1974 Big Block.
Also I do not mind a used or reman if anyone wants to sell one.
Thanks for the help folks!
Texxas
:flag
Team Owner
Joined: Jun 2001
Posts: 43,136
Likes: 155
From: Thomson Georgia
Re: Carb Recommendations for a 1974 Big Block please. (Texxas)
I just put on a Holley 750dp and I love it on my SB..I am sure it would be great on a BB...I have heard Great things about Demons as well
Race Director
Joined: Apr 1999
Posts: 15,133
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From: NM
Re: Carb Recommendations for a 1974 Big Block please. (Texxas)
What is the car being used for? What intake?
A street car with stock intake?... stay with the tried and ture Q-jet.
A race car with high rise aluminum intake?... Then a good Holley as it is more adjustable at the strip.
All depends upon what you want to do with the car.
tom...
A street car with stock intake?... stay with the tried and ture Q-jet.
A race car with high rise aluminum intake?... Then a good Holley as it is more adjustable at the strip.
All depends upon what you want to do with the car.
tom...
Race Director
Joined: Mar 1999
Posts: 10,258
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From: Calif.
Re: Carb Recommendations for a 1974 Big Block please. (Texxas)
Need cubic inches of engine and maximum RPM. Then use the following formulas to get in the ballpark:
STREET CARB:
RPM x displacement / 3456 x .85 (85 percent volumetric efficiency.)
RACE CARB
RPM x displacement / 3456 x 1.1 (110 percent volumetric efficiency.)
Example, a street-driven 454:
5,000 x 454 / 3456 x .85 = 558 CFM (theoretical).
Example, a race-only 454:
8,000 x 454 / 3456 x 1.1 = 1,156 CFM (theoretical).
EDIT: Duh. I forgot something IMPORTANT. You have to split the difference between those two figures above!
Take your 1,156 CFM carb and your 558 CFM carb from above. Subtract 558 CFM from 1,156 CFM and you get 598 CFM. Divide that by two and you get 299 CFM. Now add 299 CFM to 558 CFM (or subtract it from 1,156) and you get 857 CFM.
Therefore I would recommend using an 850 CFM carb for your car. (If it's a 454 like the examples above.)
Sorry about that.
[Modified by The Dude, 12:30 PM 12/19/2001]
STREET CARB:
RPM x displacement / 3456 x .85 (85 percent volumetric efficiency.)
RACE CARB
RPM x displacement / 3456 x 1.1 (110 percent volumetric efficiency.)
Example, a street-driven 454:
5,000 x 454 / 3456 x .85 = 558 CFM (theoretical).
Example, a race-only 454:
8,000 x 454 / 3456 x 1.1 = 1,156 CFM (theoretical).
EDIT: Duh. I forgot something IMPORTANT. You have to split the difference between those two figures above!
Take your 1,156 CFM carb and your 558 CFM carb from above. Subtract 558 CFM from 1,156 CFM and you get 598 CFM. Divide that by two and you get 299 CFM. Now add 299 CFM to 558 CFM (or subtract it from 1,156) and you get 857 CFM.
Therefore I would recommend using an 850 CFM carb for your car. (If it's a 454 like the examples above.)
Sorry about that.
[Modified by The Dude, 12:30 PM 12/19/2001]
Thread Starter
Instructor
Joined: Apr 2001
Posts: 174
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From: Flower Mound TX
Re: Carb Recommendations for a 1974 Big Block please. (Tom73)
The car is being made to be a street driven car with a small mean streak..:). This is my toy.
I am having a TH400 put back in the car as the 700-R4 that came with the car when I bought it three months ago is in need of bigtime work.
I want a solid carb that is good for solid driving and can get up and go when the mood hits..:)
Thoughts??
Texx :flag
I am having a TH400 put back in the car as the 700-R4 that came with the car when I bought it three months ago is in need of bigtime work.
I want a solid carb that is good for solid driving and can get up and go when the mood hits..:)
Thoughts??
Texx :flag
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Safety Car
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From: Clymer PA
Re: Carb Recommendations for a 1974 Big Block please. (Texxas)
Texxas:
Don't go with a 650 :nono: . I would suggest nothing smaller than a 800cfm carburetor....a 750cfm carburetor would be pushing it, but you could get away with it probably. You have to feed those cubic inches!
Don't go with a 650 :nono: . I would suggest nothing smaller than a 800cfm carburetor....a 750cfm carburetor would be pushing it, but you could get away with it probably. You have to feed those cubic inches!
Race Director
Joined: Nov 2000
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From: Waterloo ontario Canada
Re: Carb Recommendations for a 1974 Big Block please. (bence13_33)
I agree with Bence. A 650 is too small and a 750 is minimum. I personally like the 850 double pumpers. Unless set up carefully they tend to be a bit harder on gas. I would go with a Demon 850 double pumper. The demon has screw in air bleeds. I would also drill the throttle plates to allow more adjustablility of the idle screws. I am on my 4th 850 and every one has had to have the throttles drilled, I have never owned a demon or worked on them. I have heard there is a number of problems with them but compared to my personal experience with Holley I would give them a try. I stick to holley because I know them and can fit them.
Burning Brakes
Joined: Feb 2001
Posts: 929
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From: Marietta GA
Re: Carb Recommendations for a 1974 Big Block please. (SteveG75)
Do you need a spreadbore or squarebore? I don't think Demon or Holley makes a spreadbore bigger than 650 or so with a double pump, but I could be wrong. I have a Holley 4011 800 CFM spreadbore DP and it worked great on my 427 until I rebuilt the motor and couldn't dial it in. I am going to a 795 cfm Q-Jet but have not decided as to whether or not I am going to sell the Holley.
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Carb Recommendations for a 1974 Big Block please. (norvalwilhelm)
Why didn't you just go with a performance rebuild on the 700? If your not a real racer 3.90 rear gears and a 700 are hard to beat.
Drifting
Joined: Jul 2001
Posts: 1,418
Likes: 1
Re: Carb Recommendations for a 1974 Big Block please. (Texxas)
"The car is being made to be a street driven car with a small mean streak... This is my toy"
Texxas,
A carb alone is not going to help.It is a start but you need a total package.You still have not told us what intake you have so I assume it is stock and you have stock internals.Cams manifolds and headers is what wakes BB's up
Why don't you turn that small mean streak into a large one? A little extra work but not that much extra cash compared to the results.
Texxas,
A carb alone is not going to help.It is a start but you need a total package.You still have not told us what intake you have so I assume it is stock and you have stock internals.Cams manifolds and headers is what wakes BB's up
Why don't you turn that small mean streak into a large one? A little extra work but not that much extra cash compared to the results.
Thread Starter
Instructor
Joined: Apr 2001
Posts: 174
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From: Flower Mound TX
Re: Carb Recommendations for a 1974 Big Block please. (mountainmotor)
This my first car project and am wide open to ideas and "extra work". :)
The cam, intake, exhaust etc is stock and the engine has a fresh rebuild. Automatic tranny.
Thoughts on upgrades without a lot of cash..??
Texx
:flag
The cam, intake, exhaust etc is stock and the engine has a fresh rebuild. Automatic tranny.
Thoughts on upgrades without a lot of cash..??
Texx
:flag
Drifting
Joined: Jul 2001
Posts: 1,418
Likes: 1
Re: Carb Recommendations for a 1974 Big Block please. (Texxas)
"Thoughts on upgrades without a lot of cash..??"
Oh yeah there is! More than one way to skin a cat!
Ran out of time for today but do you know or can you find out what valve springs you have or what might have been done to the heads like guides cut down ect?
I nite and day difference in performance is in the makes here.
Oh yeah there is! More than one way to skin a cat!
Ran out of time for today but do you know or can you find out what valve springs you have or what might have been done to the heads like guides cut down ect?
I nite and day difference in performance is in the makes here.
Race Director
Joined: Jun 2000
Posts: 10,036
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From: FL
Re: Carb Recommendations for a 1974 Big Block please. (mountainmotor)
Automatic transmission. You are going to be a lot happier with a vac secondary vice a double pumper.
I would not be expecting any radical gains i HP or driveability by swapping carbs. The gain mostly comes from someone who knows how to tune one type vice another (i.e. Q-Jet versus Holley).
Personally, I like the Q-Jet. 795 cfm, mechanical secondaries with the air valve that opens on demand. I know people that run 12 sec street/strip cars with a Q-jet.
I would not be expecting any radical gains i HP or driveability by swapping carbs. The gain mostly comes from someone who knows how to tune one type vice another (i.e. Q-Jet versus Holley).
Personally, I like the Q-Jet. 795 cfm, mechanical secondaries with the air valve that opens on demand. I know people that run 12 sec street/strip cars with a Q-jet.
