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what is the purpose of the single elongated hole on one side of a small block intake manifold carburetor pad and the two round holes on the other side? Why are both sides not the same?
IIRC, the oval hole is for the upper plane , the two holes feed the lower plane.
It has to do with distribution, using the oval in the upper plane gives better distribution because the floor of the manifold on that side is closer to the carb. The two holes on the other side keep the flow going down for longer before they get distributed, so there isn't any "short circuiting".
I am going to suggest that if you measure teh depth of the two holes thru the aluminum, you will find they terminate the same distance above the bottom of that plane, as the bottom of the carb terminates above the top plane (oval hole).
That's for an installation where the 4bbl carb is mounted "sideways" - so to speak. The primaries go through the two small holes; the secondaries through the large oval slot.
Last edited by tuxnharley; 10-27-2016 at 04:10 PM.
That's for an installation where the 4bbl carb is mounted "sideways" - so to speak. The primaries go through the two small holes; the secondaries through the large oval slot.
All of those sexy looking manifolds are chiefly about creating even air/fuel distribution to the cylinders and minimizing perturbations in the airstream....various configurations have been tried with prob some minimal improvement but I can't say if you can feel it in the 'seat of your pants'...
All of those sexy looking manifolds are chiefly about creating even air/fuel distribution to the cylinders and minimizing perturbations in the airstream....various configurations have been tried with prob some minimal improvement but I can't say if you can feel it in the 'seat of your pants'...
PERURBATIONS: 1 : the action of perturbing : the state of being perturbed. 2 : a disturbance of motion, course, arrangement, or state of equilibrium; especially : a disturbance of the regular and usually elliptical course of motion of a celestial body that is produced by some force additional to that which causes its regular motion.
PERURBATIONS: 1 : the action of perturbing : the state of being perturbed. 2 : a disturbance of motion, course, arrangement, or state of equilibrium; especially : a disturbance of the regular and usually elliptical course of motion of a celestial body that is produced by some force additional to that which causes its regular motion.
Morphs into the human equivalent..........otherwise known as a ***t disturber.
PERTURBATIONS: 1 : the action of perturbing : the state of being perturbed. 2 : a disturbance of motion, course, arrangement, or state of equilibrium; especially : a disturbance of the regular and usually elliptical course of motion of a celestial body that is produced by some force additional to that which causes its regular motion.
Sounds like it comes from the same root word as "turbulence"- thus trying to smooth it out............
IIRC, the oval hole is for the upper plane , the two holes feed the lower plane.
It has to do with distribution, using the oval in the upper plane gives better distribution because the floor of the manifold on that side is closer to the carb. The two holes on the other side keep the flow going down for longer before they get distributed, so there isn't any "short circuiting".
I am going to suggest that if you measure teh depth of the two holes thru the aluminum, you will find they terminate the same distance above the bottom of that plane, as the bottom of the carb terminates above the top plane (oval hole).
Doug
An Engineer at Edelbrock in the 80's, Jim McFarland, told me it was thought to even out the volume of the plenum of the high plane with the lower plane. The open volume between the two holes was thought to equal the deeper volume in the lower plenum and even out the throttle response. When he pioneered the singled plane manifolds all the old school copycat fads were tossed out and the manifolds redesigned.
You do not see the same three-hole design practice in newer computer designed manifolds, but that does not rule out achieving equal plenum volumes in the castings.
An Engineer at Edelbrock in the 80's, Jim McFarland, told me it was thought to even out the volume of the plenum of the high plane with the lower plane. The open volume between the two holes was thought to equal the deeper volume in the lower plenum and even out the throttle response..
That thought crossed my mind, but the divider doesn't come close to making up for the different volumes. You still have those two long holes that add extra volume to that side
Looking into and at the bottom.... what is the purpose of the '58' looking ribs...?
Does that have something to do with "atomizing the fuel"?...
That's the surface directly above the heat riser passage, also known as a "hot spot" to aid vaporizing liquid fuel as quickly as possible to get the most even distribution. The ribs offer more hot surface area than if the surface was flat.
There's a lot of complicated physics going on in a carburetor-manifold system. In his book, Dave McClellan said it's a wonder that they work at all. They do as long as the carb is calibrated rich enough to keep the leanest cylinder out of lean misfire, but that costs about an extra five percent fuel compared to port or direct injection with properly matched flow rates.
That's the surface directly above the heat riser passage, also known as a "hot spot" to aid vaporizing liquid fuel as quickly as possible to get the most even distribution. The ribs offer more hot surface area than if the surface was flat.
There's a lot of complicated physics going on in a carburetor-manifold system. In his book, Dave McClellan said it's a wonder that they work at all. They do as long as the carb is calibrated rich enough to keep the leanest cylinder out of lean misfire, but that costs about an extra five percent fuel compared to port or direct injection with properly matched flow rates.
Duke
Yes. I started reading about dual plane manifolds and the handling of induction pulses and stopped after about the third page I think...
That's the surface directly above the heat riser passage, also known as a "hot spot" to aid vaporizing liquid fuel as quickly as possible to get the most even distribution. The ribs offer more hot surface area than if the surface was flat
Duke
Interesting. So the cross over is for more than just aiding in cold start drivabilty. It looks like the high performance and after market manifolds were designed to take advantage of that, where the cruder base model castings did not.
Perhaps that had something to do with aluminum castings vs cast iron?
Why do so many racers block off the cross over if it can aid in better fuel vaporization and even distribution to all cylinders?
10-27-2016, 03:37 PM
Aluminum Intake Curiosity Question
