Milling of a 810 casing W-2 head
Dang! This is an awesome thread.
I was really debating about using cast iron 80's technology open chamber heads....
That W2 head is MILES ahead of any, and I mean ANY 23 degree GM stuff. The only GM 23 degree stuff it won't outrun is the raised runner stuff and that's what the W5 was for. With work, that's a pretty bad assed head on its own, it just takes a ton of work and quite a bit of welding to get it where it's happy.
BTW, I forgot to mention that when flowing on a bench, you have nothing in the hole. When the head is on the engine, and you are at the two most critical times in the power making cycle, the opening of the intake valve, and then what is called the overlap triangle, the piston is making up the bottom of the combustion chamber.
Anything you can do to get the flow happy at that time, you'll make more power. If you just think about what that looks like in your mind, you can develop a picture about why a later opening intake cycle with a quicker lobe can make more power, idle better and cleaner and have more low end power without a loss in top end power.
The last thing you want is to open that intake valve any earlier than you have to for your RPM range. For one thing, the piston is right there, in the way. And as the piston is moving around TDC and you open the valve earlier than needed and you'll have the piston pushing the intake charge right back up the port.
Here is another example of why Rod to stroke ratio is important, especially in induction limited combinations. IMO, a higher rod/stroke ratio can always use a quicker lobe, because the piston is hanging around TDC longer. That means what is ok for a lobe for a lower rod/stroke ratio may be not as good as it could be for a higher r/s ratio. That's because the overlap triangle looks different when overlaid with the motion of the piston. That's why cam timing that moves the intake opening and exhaust closing around to get the LSA wider to "correct" what is thought to be an idle issue can be a bad thing for power.
I like to see a very leaky overlap triangle rather that a triangle that looks more like a cam lobe than a triangle.
All this stuff matters if you want to get the most for your dollar. It doesn't cost any extra to sort this stuff out while you are building your combination. It gets expensive when you have to fix it after you've already settles on the hard parts.
It all matters.
