As always, thank you for taking the time to give your perspective. I recognize the speed over the apex is way to fast, but so far enlarging the pinch has only made it faster. In my experience increasing the height of the pinch doesn't help much, it's more width that is needed. I have another port in this same head with a relocated pushrod pinch. I'll spend some more time on that one.
That has been my objective as well. It only takes a few thousandths bump at high speed to create problems.
Look up pittsburgracer's Speedmaster head threads. He showed how he was tubing the common wall head bolt hole and the pushrod hole so he could grind right up to it.
On the factory CNC head that I bought last year, I felt the bowl and throat were too large for a 265-270 cfm port. The pinch can handle that much flow with a little cleanup.
Solve it? No. Still a lot of area needed at the apex and a short side to seriously re-work, especially if you are feeding a stroker motor.
This thread, mentioned in post 14 and picture in post 329.
My statement is based on 1 SM factory CNC head that I purchased last year on Black Friday. In my opinion (which could be wrong), that one head had a throat that was way to large at 93% and a port volume that was a little too large for the 265-270 cfm that it flowed. It had a 2.02 valve. To get the throat to a more reasonable 90-90.5%, a 2.08 valve would need to be used. My guess is that a good 2.08 valve job on that head would get the flow into the 280s with little other work. That should put the port velocity into a little better range as well. I do not know if all SM CNC heads had the same specs as mine.
Harland Sharp and Hughes both have offset rockers. B3 Racing Engines is a great source for valvetrain solutions.
Yes, I discovered that ~32years ago, the valve changes from peripheral flow control to an airfoil/aerodynamic wing during the lift cycle...the critical point is different head-to-head, and will change in the same head depending on what You do to it. The valve is partially blocking excess negative pressure from dis-orienting the established directional flow. It's aerodynamics outside-in, but less predictable, & more complicated. Thx again for documenting Your testing.
Isn't the small block Edelbrock Victor designed for using a big block rocker arm?
That would seem like it would be the easy button to an offset rocker, but I'm not familiar with how far the stands or mounts would need to move in order to utilize the BBM rocker system.
Here is the note from the instruction sheet in the Edelbrock Victor Small block head, part number 61729. It says "big Block Mopar Wedge" and specifies minimum of .150" intake offset. if these keep showing up in stock maybe we will start to see more guys using them. I wish I had the funds to try them.
Are you going to have to fabricate some adapter plates to fit the manifold to the heads? Are there issues with the manifold width? I know the bore spacings are slightly different.
EXACTLY... that's why I buy the SM heads bare, I dont want to try to fix there "cnc" job which is essentially a digitized copy of of not great porting job. Only my opinion, I'm not a pro head porter
Respectively, you should start your own thread. This particular thread is about the speedmaster SBM head, and it's not helpful to muddy it up with a completely different head and engine combination
Just taking a little time to read through this and think about it. Let's discuss this. I think things like this are key to making a port and chamber better.
This is the part I really want to discuss. It's my way of thinking that the valve is partially blocking POSITIVE pressure from re-directing the flow. That's what flow separation is. The flow separates from the short side and low velocity (higher pressure) air from inside the chamber pushes up against the high velocity (and low pressure) air stream, choking off part of the flow. Right at the valve seat on the SS air is actually traveling up the port in the opposite direction.
