Here's a picture of a idealized Exh port. It's like a nozzle and has a very distinct Venturi shape formed at its throat in the bowl. The bowl is very deep and the high exit at the flange makes all the 4 port walls nice and long. With this idealized port once the throat is shaped right other areas after the throat on the way out to the flange are not half as sensitive to change as with the stock short depth Buick exh port, and this is true for both factory iron SB and BB heads other then the stage II heads. Also do not do a gasket matching at the flange , because as it is there is more then enough port area there. Gasket matching will only serve to make for more low rpm flow reversion which will then make the motor come on the Cam later / delay good torque production. If anything you want the outlet from the head to be smaller then the inlet to the header or exh Manifold. I will post more detail and a photo or two later this afternoon EST.
I watched a vid by Dave Vizard last night he was showing the flow path the air takes on the intake side, I’ve never seen it visually, he used dykem or some kind of machinist blue in the air stream, it was fascinating, the air doesn’t go where you think it would.
Here’s the one I watched this morning on port filling and making the port a trapezoid like Stevem mentions. I’m still looking for the other vid, be
Even better then Davids video, go watch the 3 part series ( part 1, 2 and 3 ) by Darin Morgan on YouTube called induction dynamics wet flow.
My head porting guy went to Darin Morgan‘s head porting school, then bought $200,000 in tools and equipment.
Is there any harm (or benefit) in taking this extra chunk of material around the back/intake bowl side of the exhaust guide boss down till it's even with the face of the guide boss?
I’m going to give my amateur opinion: Just trench it. I’m thinking if you remove it you’ll have a wall there so to speak
Just remove half of that 90 degree arc you have highlighted. Do so only on the intake valve bowl side . don’t make it a ditch, just grind it down enough to remove that lip while also leaving a slight transition from that vertical port wall to the top of the guide. your going to need a small ball headed Burr to get that transition right.
I have watched these two and tons of other porting videos on line and what you guys porting away at home without the aid of a flow bench and a pitot probe need to keep in mind which is a big factor is this. In these two video links posted here is that both the SBM head and the SBF head seen / used in these videos have a 18 to a 20 degree valve inclination angle, and your Buick heads have a far shallower valve inclination angle. This means that what you see for porting done in these videos many not only not work as well, but may reduce the amount of stock flow your heads have . To a home porter without a flow bench using your eyes and thinking you know what to grind on and going for a more streamlined form to get more air into ( Intake) or out of ( Exh ) the chamber can really screw you up! Once again let me say again that all the stock Buick iron heads other then the stage II have very shallow valve bowl and not much short turn height for the size of the valve bowl throat used. And let me say again and along these same lines that the factors stated above mean the good or bad changes in air flow levels will take place with far less metal removal then what you are likely to have seen in many porting videos of other heads.
Just to be sure where on the same page here, I am talking in specific about the valve INCLINATION angle, not whatever angles are part of the valve job.
