size

[JETEATER]

What size carb do you grt when you take a 850 baseplate and put it on a
750

[Squirtin Thunder]

What size carb do you grt when you take a 850 baseplate and put it on a
750
Why would you do that ???
Now are you planning on blending all the transitions or just putting it on ???

[JETEATER]

I had one before but sold it.
I just put one together today blended all the transitions and cut off the
choke horn.
It was i hotrod mag a year or so ago

[SmokinLowriderSS]

Your limiting factor is not going to be the size of the butterfly plates, but the size of the venturi the boosters are in. I'm willing to bet your 750 body with all that work to put 850 plates on it will be a 750 as far as airflow goes.
Also, I'm not too convinced there is anything to be gained by sawing the choke horn off. Look at it's area, and then look at the area of the 2 venturis below it. It's not a restriction to airflow anywhere. Actually, unless you smooth the transitions where the horn casting USED to be really well, you could cause curls (turbulence) in the flow into the primary venturis, actually REDUCING airclow capability. One of the unknown effects of a air filter housing BASE PLATE is it smooths the airflow going into the carb. Carbs actually loose flow by sucking arround their own corners instead off of a smopothly arched plate (from a Holley book I have).

[JETEATER]

I will find out if it works better on friday
I found the write up in Hotrod it turns it in to a 790 cfm

[H2OT TIMES]

Your limiting factor is not going to be the size of the butterfly plates, but the size of the venturi the boosters are in. I'm willing to bet your 750 body with all that work to put 850 plates on it will be a 750 as far as airflow goes.
Also, I'm not too convinced there is anything to be gained by sawing the choke horn off. Look at it's area, and then look at the area of the 2 venturis below it. It's not a restriction to airflow anywhere. Actually, unless you smooth the transitions where the horn casting USED to be really well, you could cause curls (turbulence) in the flow into the primary venturis, actually REDUCING airclow capability. One of the unknown effects of a air filter housing BASE PLATE is it smooths the airflow going into the carb. Carbs actually loose flow by sucking arround their own corners instead off of a smopothly arched plate (from a Holley book I have).
So is this the idea behind a velocity stack????????

[SmokinLowriderSS]

Here's some info I found on velocity stacks. It's cut I pasted, from various parts of the web, but tends to agree.
From a motorcycling forum:
It is called a velocity stack because it is supposed to increase the velocity of the air going into the engine, in theory. The shape of the curve in the stack creates a pressure differential and increases the speed of the air past the curve. Like a wing on an airplane, the wing has a curve on the bottom differnt from the shape of the top of the wing, which creates a pressure differntial between the air on the top of the wing and the air on the bottom, in turn creates lift.
The theory of a velocity stack is based on the venturi principle that air increses in speed as it is constricted. On an intake, it is supposed to do the same thing, but most times the turbulence created by the shape and mounting direction of the stack defeats the intended purpose. On a wing they sometimes put vortex generators on the top of the wing either leading edge or trailing edge, to create littel tornado type spirals which in turn create an even bigger differential between the top and the bottom. That is the theory behing the tornado intake for cars. That cheap little product that you put in the car increases power and fuel economy, so they say.
K&N.com:
Straight cut velocity stacks, for example, pose a unique problem. Exposed to the outside air, velocity stacks experience a phenomena that actually hinders performance at high speed. We are referring to stacks and air horns that protrude through the hood and extend into the air stream so the direction of the air rushing over the car is at a perpendicular angle to the length of the tube.
Air moving rapidly over these stacks create turbulence inside the opening. At high speed, the rushing air tends to create a partial vacuum inside the tube. The condition is counterproductive to air flow. The phenomena also effects open carburetors. The higher the ground speed, the greater the problem. Vacuum created by the engine is trying to coax air into the cylinders and the high speed air flowing over the open end of the stack is causing resistance.
Another motorcycle performance forum:
A velocity stack smooths the flow of air entering the carb and can also provide a stronger "sonic" ram effect. How it works. For those who care, when the intake valve opens a negative pressure wave travels up the intake until it hits the end of the velocity stack. The negative pressure wave reverses when it hits an expanding cone or opening and becomes a positive pressure wave traveling back down the intake towards the valve. If the positive pressure wave is timed to hit the valve just before it closes, then more mixture gets crammed into the engine, and you get a boost in torque. That's why the intake tract length has to be optimized for the engine rpm where you want the boost and also for the amount of intake duration. A velocity stack change the intake track lenght.
Tall = moves the powerband down
Short = moves the powerband up
I have a cool photo in my BBC book of an old FI Can Am motor with 8 injector velocity stacks atop it, 1 per cylinder on an isolation manifold. They were cut to 2 different heights to widen the RPM range of the most power. I'll give them some credit as a tuning aid to help controll carb reversion in single-throat aplications such as motorcycles or isolated runner FI units. Atop a 4-barrell that is atop a manifold, I call them "bling".