Port Mismatch

[GM-DR]

SBC Drag Racing Engine---RPM Band 5300-7300 +-/ Ported OEM heads=port entrance 1.18x1.95---Ported Victor JR =port exit 1.22x1.95---How much Is that .020 mismatch on the two sides costing me ? Best Performance to date 11.31/116 MPH @ 3400#s ( Upgrading to Better Heads or Camshaft is NOT legal or possible) Thanks For Your Input

[Newold1]

Little to nothing. In a port on that SBC head that .020" per isn't even as deep as the boundary air layer flow against the wall. If its together no need to port match that and even if it is not you won't see any appreciable power difference in my experiences.

[MadBill]

I've read a number of references that said 0.020" misalignment is functionally identical to 0.000".

[steve cowan]

On one of my speedtalk CD
Phil martin says they oversize the intake 50-100 thou on purpose in nascar back in the day (circa 1990s)
He mentioned boundary layer but didn't go into detail,
The question I ask does the boundary layer still exist when the valve opening and closing 60 times a second??

[GM-DR]

Thanks for the answers !!!!! --it appears that everyone here has drawn the same conclusion---I now feel better installing this

[Newold1]

If air is moving over a surface there will be a boundary layer.

[steve cowan]

If air is moving over a surface there will be a boundary layer.

Yes I hear what you are saying, I have thought in the past that turbulent air with fuel in and out of suspension might make the mixture stick to the port walls.
Now I am not sure so I am going back to reaserch department to read up on laminar and turbulent flow, boundary layers and port wall finishes for different applications

[MadBill]

It's been authoritatively stated in previous S/T threads (DV's among others) that due to its velocity, engine airflow is always turbulent.

[steve cowan]

It's been authoritatively stated in previous S/T threads (DV's among others) that due to its velocity, engine airflow is always turbulent.

agreed Bill,
just read 64 pages on port wall finish-now i am tired

[Stan Weiss]

Since the BBC Rectangle port intakes will work fine on Oval port heads i don't think you have anything to worry about.

Stan

[David Redszus]

A port with laminar air flow will exhibit streamlines that are parallel to the port wall. The streamlines will move faster down the center than at the wall. At some small distance from the wall the flow will become zero and is defined as the boundary layer.

The Reynolds number consists of: port diameter * air velocity * air density / air viscosity. The Reynolds number will define the transition from laminar to turbulent air flow. Assuming that port diameter, air density and air viscosity do not change (a false assumption), the Reynolds number will become a function of air velocity.

As air velocity increases, the streamlines break up into filaments that become turbulent and strike the port wall eliminating the boundary layer. This turbulent condition usually exists whenever inlet air is flowing with the valve open. The turbulent condition increases the friction factor and the air becomes sensitive to wall surface texture.

A change in pipe diameter, either increasing or decreasing, will reduce air flow. The flow reduction is defined by K, the resistance factor. The K factor adds a specific equivalent length to the system and causes a drop in pressure, which reduces flow.
Small changes in pipe diameter can be ignored as being insignificant. For example, a 5% difference in diameter would add 0.008, (10% = 0.030, 15% = 0.06), to overall length.

While pipe step changes may have little effect on air flow, the same cannot be said for fuel rivlets attached to wall surfaces.
Fuel vapor will behave differently than dry air, due to changes in density, viscosity and velocity.

[GRTfast]

If air is moving over a surface there will be a boundary layer.

Yep. I was going to say this, but you did first!

[David Redszus]

If air is moving over a surface there will be a boundary layer.

If that is true, then what is the difference between laminar flow and turbulent flow?
Both are moving but both do not exhibit similar boundary layers.

[digger]

If air is moving over a surface there will be a boundary layer.

If that is true, then what is the difference between laminar flow and turbulent flow?
Both are moving but both do not exhibit similar boundary layers.

[BOOT]

In my opinion sometimes it's simply a step of larger intake into smaller head helps stop fuel from running down the runner at lower demand rpm.