Carb Venturi Size for 470 ci

-
mopowers

mopowers

Well-Known Member
Joined
Feb 15, 2006
Messages
8,534
Reaction score
4,748
Location
West Sacramento, CA
Consider the following engine/drivetrain combo in a 66 Dart:

470 ci B-stroker (10.5:1 SCR)
SFT cam 260-ish* @ .050" and 0.650"
Modern Cyl Head cnc'd Edelbrock RPM heads w/ Victor 383 manifold and 1.5" open spacer
727, 4.10's, and 30" tall tire

The car will be driven a lot on the street and taken out to the 1/4 mi. track as well. Which carburetor venturi/throttle bore size would you go with of these three choices? I've got all three on the shelf so I'll be trying them all when the time comes, but I'm curious which one you guys think would provide the best street and track performance.
  1. 1.375" venturi, 1.75" throttle bore (BIGS "950")
  2. 1.450" venturi, 1.75" throttle bore (Brawler "950")
  3. 1.5625" venturi, 1.75" throttle bore (Holley 4781 "850")
 
mopowers said:
Consider the following engine/drivetrain combo in a 66 Dart:

470 ci B-stroker (10.5:1 SCR)
SFT cam 260-ish* @ .050" and 0.650"
Modern Cyl Head cnc'd Edelbrock RPM heads w/ Victor 383 manifold and 1.5" open spacer
727, 4.10's, and 30" tall tire

The car will be driven a lot on the street and taken out to the 1/4 mi. track as well. Which carburetor venturi/throttle bore size would you go with of these three choices? I've got all three on the shelf so I'll be trying them all when the time comes, but I'm curious which one you guys think would provide the best street and track performance.
  1. 1.375" venturi, 1.75" throttle bore (BIGS "950")
  2. 1.450" venturi, 1.75" throttle bore (Brawler "950")
  3. 1.5625" venturi, 1.75" throttle bore (Holley 4781 "850")
Click to expand...
1.
 
The 1.56 carb would be my choice. It’ll handle more. It’ll also be perfectly streetable if tuned up.
 
I run a proform 950 and it's 99% street use. I've always preffered a holley style carb.

That engine will gladly handle the biggest square bore carb and be very responsive.

Also, unless you don't know how to tune a carb, i'd stick with mech sec.
 
roccodart440 said:
I run a proform 950 and it's 99% street use. I've always preffered a holley style carb.

That engine will gladly handle the biggest square bore carb and be very responsive.

Also, unless you don't know how to tune a carb, i'd stick with mech sec.
Click to expand...

Thank you. Do you know what venturi size your proform 950 has? I'd guess it's identical to the brawler at 1.45"?

And yes, mech secondaries only. I haven't owned a vac secondary carb since high school.

I think it's interesting that people generally refer to carbs by their fake cfm ratings and disregard the venturi and throttle bore sizes for the most part.
 
That cause most don't know that a 950 NAME on a carb, doesn't mean it'll flow 950.
I'm happy with a 4781 on my 440, with a lot less cylinder head than you.
 
mopowers said:
I think it's interesting that people generally refer to carbs by their fake cfm ratings and disregard the venturi and throttle bore sizes for the most part.
Click to expand...
That’s because most people don’t understand this.
They just take what the manufacturer says it is.
Holley say this carb is a 650 because it flows 650, then it’s a 650. The relationship between the sizes is never really understood and nearly never talked about here.

Some members talk about it but have not included any lessons
 
I learned my venturi size lesson with an antique gold claw RS... and the four different sleeve sizes that came with it..... (bought it used from a friend, he included the extra sleeves.)
 
Nice! I wanted to pick one of those up. At the time, it would have been a case of the horse before the cart thing. So, I never got one. Must have been fun screwing around with that thing.
 
rumblefish360 said:
Nice! I wanted to pick one of those up. At the time, it would have been a case of the horse before the cart thing. So, I never got one. Must have been fun screwing around with that thing.
Click to expand...
Funny thing is, I never messed with it, cause I didn't have to. He dialed it in on a roller 408 Ford, I put it on a roller 406 Chevy, and never even pulled the bowls off. Whatever the jetting was, it ran great. (I didn't find out how "big" it was, or what jet, till I rebuilt it cause it sat for a few years. It had the next to the biggest sleeves I had for it, the blue ones)
 
Out of curiosity, I decided to call up Holley (I know - I'm a glutton for punishment) to ask how a '950' flows more cfm than an '850' with a larger venturi with the same throttle bore size as the '950.' He said the 950 flows more because it's about "air speed," not venturi size. My BS meter was starting to sound, but I what do I know.
 
mopowers said:
Out of curiosity, I decided to call up Holley (I know - I'm a glutton for punishment) to ask how a '950' flows more cfm than an '850' with a larger venturi with the same throttle bore size as the '950.' He said the 950 flows more because it's about "air speed," not venturi size. My BS meter was starting to sound, but I what do I know.
Click to expand...

Smaller is bigger, makes perfect sense.. works the same way with beer.. lmfao
 
You must log in or register to reply here.
-

Back
Top