Forgive the upcoming AJ length post....
Answering the question first, I gave the answer above. How far you want to take it is your (or machinists) call.
Wyrmrider made a good mention about cylinder wall flex. I didn’t think about that comparison.
Now, about un shrouding the valves. Yes, it’s a win win for what ever head your have on top.
And no on what makes a W5 head work best is no different than any other head in general because of not what the head is but how a head responds to the available space around it.
Now just to touch on some science.....
The bigger the bore, the more potential the head can flow. Increasing the stroke also helps this. A cylinder head can only flow so much. When you reach this limitation, power falls off in the upper rpm range. This is dependent of the bore and stroke as well as the overall CID of the engine. What or where this limitation is has been discussed and reasonably solved with knowing the cylinder heads port size. (Cross sectional area) Over all shape and flow abilities are also coupled to this. But to back it up a minute and use the KISS method, the port window is the key.
This is why myself and Yellow Rose like the W2/5 head over the Trick Flow heads. Even though the trick Flow has a 300 cfm rating, it is flowing that much through a smaller window. Let’s take this into our imagination a second and blow proportions out.
Using an analogy from Dave Freiberger, if you have a doorway that’s 36 inches wide, how many people can get through in a minute to fill the concert hall? Now what if you have a door way double the size?
The first smaller door can have people come in jogging at 300 feet per minute, the larger doorway can have people jogging at 280 feet per minute.
Who’s getting in more people through the doorway?
To continue on.....
The cylinder head can only more so much air. There is a limitation. Increasing the size of the gathering hall (the cylinder after the door way) for more people than the doorway can let in, is the same as putting a small doorway in on any hall. (Engine)
If the doors are open for only 1 minute, then the head isn’t big enough. (Head to small) Repeat this process over and over to fill the hall, it’s like filling multiple arenas.
RPM shortens the doorways ability to completely fill the area. This is why you have 318 heads on a 360 making a ton of torque down low and running out of breath up top.
Brett Miller whom had a hand in the new Edelbrock Victor head, engine masters build challenge engine limited the size of the engine to 376 - ish or so cubes as not to have the head run out of breath in a huge cylinder filling with the coupled high RPMs expected from the engine.
What he ended up with was a highly efficient engine at a smaller size. The RPMs were high and power was made all the way to the top of pull with a small duration cam.
The large doorways to fill the arena were always open enough to fill the arena completely. Even though they were open only for a short time.
A much larger engine would run out of breath earlier.
While it’s not a bad thing or way to go about it, you don’t need a huge engine to be combined with high rpm in order to make the head work. You should look to a balance to make it work great. And IMO, that 372 - W2 is an awesome combo you have that I am also working on. I think it is an excellent combo ready for a reasonable sized cam to tear up the tarmac, where ever that may be.
On my up coming W5, it will be a (I hope) huge stroker that peaks early in RPMs for less stress and a foundation for well prepped Victors later.
I do believe the W5 set up combo I’m working on is a 9 second capable mill. A very light Duster will be employed. And it shouldn’t have to turn RPMs like crazy in order to do it.
I hope I explained that well enough.
I have posted my W5 numbers here before on the big and small test size bores. 4.03 vs 4.180 equaled about a 14 cfm difference on the big lift end. What you can wring out of 14 cfm is also a very build dependent thing. Back to the KISS method and math on CFM flow and possible power to ba made is, CFM X’s 2 which equals 28 HP. On a race mill, you can go more by a fair margin. CFM X’s 3 is not unheard of. (42+ hp)
