It's a pretty broad brush to paint with. Depends on the ports design. You can have a port that works excellent and then open up that pinch as big as you can and watch it lose all of its low lift velocity which is airflow...as with a magnum head.
If it didn't matter in that head they would have had the 308 pushrod holes and not that smaller Magnum pinch. People need to be more specific. Specifics come with understanding. You can lead somebody into making a big hole and believing that it's all about making big holes. The Magnum head is 150 CC's and it's hard to get it much bigger than 160 to 165cc. That's why this **** gets confusing because you'll have people tell you this.. tell you that ...and then tell you it's about the quality of air at the same time... not necessarily the amount of air. .. then show you a bunch of power on a Dyno with a head that falls off and doesn't have that great a quality of air. One gathers that while important..its not as important as some say it is. Not to veer off ..but Eric weingartner did a video where he turns the test pressure way up and gets the port to go turbulent sooner expressing its simulation to a running engine .... not quite. Now that leads a lot of people to believe that if you don't run an absolutely High test pressure 28-40" the entire time testing that you will not have accurate info... and while that might be partially true...neither is flowbench to begin with.
Go watch the video with the camera inside the intake manifold where the pulses are yanking back and forth ...that's not a steady flow depression is it.
All of this stuff is somewhat speculatory but it's what we use to try and measure what we're doing. So saying this or that doesn't matter and attaching nothing of specifics to it isn't very helpful.
Thanks for mentioning my thread..
It seems internet forums has just as short of a memory as an old magazine 40 years ago..
No matter how much work you put into it. Few actually do any research to summarily answer their own questions.
As far as Weingartner's experiment, (something I/we tried 30 yrs ago) I/we concluded this seemingly anomalous occurrence was a function of the radius inlet being used on the head while testing.
The following is NOT intended to poke anyone's eye!
I remember a huge internet blow-up over this several years ago. That is: formed clay, or a fixed radius for testing. I remember one individual who even bragged of spending hours getting the clay shaped 'just right'.
I'll cut to the chase. PUT THE DAG GUM MANIFOLD ON IT.
There comes a time, after thousands of flow tests, we realize we are kidding ourselves if we leave the intake manifold out of the equation.
To support your statement, in reference to pushrod pinch... I did a set of 308 castings for a Super Stock application with a 1.88 valve. It flowed 258cfm. This is without exceeding the 162cc rule the NHRA for the application.
A year later, I did another set, only with a 2.02(big valve 340). Still with the port cc limit of 162.
While the low lift numbers were better, due to the increased seat area, the total flow numbers were the same.
BTW the same fixed entry was used for both heads.
A curious thing happened. I simply placed my hand flat under the bottom of the entry and the flow shot up to 265 cfm.
If not for this curious and maybe even frivolous move, we might not have changed manifolds.
In the end, the clay shapers out there kinda got it right, but to what end?
Again, put the manifold on it, unless you're only interested in half of the answer.
