Pinch point debate

[T-flow]

Because of the demand "Needed".

You can't just open the pinch(area) and think it's going to pick up. The whole intake track need's to be accounted for. There's lots of thing's that 23 sbc head has that you need to address, floor, ssr, the pinch and short wall(pushrod wall). These all need to work with what's upstream. They have a dual taper intake track. These style heads use the PRP, SSR and valve job to get what is needed, this help's aid the correct speed.

You need to look at the demand needed and min. CSA to reach your goals.

In most cases, I would rather the smaller port (per the application)than one thats too big and lazy. The air pump that can pump the fastest win's! Acceleration, thats what's going to move the car down the track!

[SchmidtMotorWorks]

I think I can explain my point better, it was, if the pinch act like a venturi it can increase the charge average velocity/density at the back of the valve just a few crank degrees before it closes, creating more momentum to the air charge pulse travel against the moving up piston.

Nope, that would be perpetual motion, you can't add density to flow with an upstream restriction.

[T-flow]

I think I can explain my point better, it was, if the pinch act like a venturi it can increase the charge average velocity/density at the back of the valve just a few crank degrees before it closes, creating more momentum to the air charge pulse travel against the moving up piston.

Nope, that would be perpetual motion, you can't add density to flow with an upstream restriction.

Bingo!

[BrazilianZ28Camaro]

I think I can explain my point better, it was, if the pinch act like a venturi it can increase the charge average velocity/density at the back of the valve just a few crank degrees before it closes, creating more momentum to the air charge pulse travel against the moving up piston.

Nope, that would be perpetual motion, you can't add density to flow with an upstream restriction.

Bingo!

T-flow you have a PM .

[gmrocket]

its 3"(bigger area) because at the head/manifold face its not 90deg to the port centerline.

Are you saying straight line?
Or right angle?

i'm saying you cant quote the gasket opening area if the head isnt a square head, like a BBC or olds etc. is it that hard to understand when you slice anything on an angle , the area of that opening/gasket will be larger than if its at 90deg?

[rookie]

My understanding is that the pinch wall can be used to push the bulk of the air on to the active wall and to better help set it up for the turn into the chamber, I have pondered if there would be an advantage to working it in a series of angles like a valve job where the min area of the pinch would be in a straight line with the active wall and the back edge would be sharp to shear the air off in a straight line as opposed to a radius that makes the it want to follow the pinch wall.

[rookie]

its 3"(bigger area) because at the head/manifold face its not 90deg to the port centerline.

Are you saying straight line?
Or right angle?

i'm saying you cant quote the gasket opening area if the head isnt a square head, like a BBC or olds etc. is it that hard to understand when you slice anything on an angle , the area of that opening/gasket will be larger than if its at 90deg?

Don't get bent out of shape, Just trying to clarify so I can better understand.

This sounds like a good reason to develop a more appropriate intake.

[SchmidtMotorWorks]

My understanding is that the pinch wall can be used to push the bulk of the air on to the active wall and to better help set it up for the turn into the chamber, I have pondered if there would be an advantage to working it in a series of angles like a valve job where the min area of the pinch would be in a straight line with the active wall and the back edge would be sharp to shear the air off in a straight line as opposed to a radius that makes the it want to follow the pinch wall.

This is part of why the gen 1 SBC is obsolete.

[rookie]

My understanding is that the pinch wall can be used to push the bulk of the air on to the active wall and to better help set it up for the turn into the chamber, I have pondered if there would be an advantage to working it in a series of angles like a valve job where the min area of the pinch would be in a straight line with the active wall and the back edge would be sharp to shear the air off in a straight line as opposed to a radius that makes the it want to follow the pinch wall.

This is part of why the gen 1 SBC is obsolete.

With the # of new heads and products made for them each year I would say there far from obsolete.

[SchmidtMotorWorks]

My understanding is that the pinch wall can be used to push the bulk of the air on to the active wall and to better help set it up for the turn into the chamber, I have pondered if there would be an advantage to working it in a series of angles like a valve job where the min area of the pinch would be in a straight line with the active wall and the back edge would be sharp to shear the air off in a straight line as opposed to a radius that makes the it want to follow the pinch wall.

This is part of why the gen 1 SBC is obsolete.

With the # of new heads and products made for them each year I would say there far from obsolete.

It depends on what obsolete means to you. In regards to a racing engine competing against other, more modern designs, yes it is obsolete.

There have been some really nice manifolds brought to market in the last 2 years, notice they didn't make a gen 1 SBC version.

[user-9274568]

There are many heads that have the opening the MIN CSA and in my eyes, that is wrong..

You CAN quote the opening because it's part of the intake tract and the secondary choke can be anywhere. Stop thinking in terms of min, and in terms of average airspeed.

The 23º is far from obsolete.

Edelbrock just introduced the SV2 and in most applications I think it's too big.

How many manifolds do you need when your dealing with a velocity limited cylinder head?

[rookie]

There have been some really nice manifolds brought to market in the last 2 years, notice they didn't make a gen 1 SBC version.

Thats true if you exclude the likes of AFR and Nelson Racing.

[rookie]

There are many heads that have the opening the MIN CSA and in my eyes, that is wrong..

You CAN quote the opening because it's part of the intake tract and the secondary choke can be anywhere. Stop thinking in terms of min, and in terms of average airspeed.

The 23º is far from obsolete.

Edelbrock just introduced the SV2 and in most applications I think it's too big.

How many manifolds do you need when your dealing with a velocity limited cylinder head?

I am not thinking of having the opening the min cs just more in line with the remainder of the port for less change in speed.

[Lockwire]

Postby rookie » Sun Mar 31, 2013 9:35 am

( BrazilianZ28Camaro wrote:I'm wondering if the pinch point may act like a venturi to increase the charge density at the back of the valve when the piston is near BDC improving cylinder filling over a longer period

That is what DV has found in his testing. )

Not to be a smart ass but I do not think that is what David wrote in one of his books, I proof read some stuff for him and I think that he said at least in what I read was that you need like I mentioned a runner with a parallel section about 3 time valve dia for 2 valve and about 4 - 5 times valve for 4 valve. From memory, so don't shoot me but, its kinda like Jon said about density. Applies to lots of runners. Stuart.

[rookie]

Postby rookie » Sun Mar 31, 2013 9:35 am

( BrazilianZ28Camaro wrote:I'm wondering if the pinch point may act like a venturi to increase the charge density at the back of the valve when the piston is near BDC improving cylinder filling over a longer period

That is what DV has found in his testing. )

Not to be a smart ass but I do not think that is what David wrote in one of his books, I proof read some stuff for him and I think that he said at least in what I read was that you need like I mentioned a runner with a parallel section about 3 time valve dia for 2 valve and about 4 - 5 times valve for 4 valve. From memory, so don't shoot me but, its kinda like Jon said about density. Applies to lots of runners. Stuart.

Sorry I thought he was referring to a ramming effect like DV has spoke of in the past I believe in his carb and intake book. The book you are referring to is his porting book and I don't know if he writes about it in that.