Speedmaster heads for SBM
100% untrue horseshit. You are repeating why you’ve heard, not what you know.
You do know about rules of thumb don’t you? There are many of them and they are used for quick and dirty calculations that don’t require a bunch of math.
Let me give you one.
For in-line wedge heads, you want the intake valve to be 50-52% of bore diameter. That means with a 3.910 bore, you SHOULD be using (at a minimum) a 1.955 and a maximum of 2.0332 valve diameter.
You can do the math and figure out that most factory junk doesn’t follow that rule. and I’ve seen guys argue that same worn out velocity bullshit that always comes up. and it’s WRONG.
The reason the OEM’s don’t follow that rule isn’t because a smaller valve/port has more velocity (if you have ever ported heads and intakes and worked with a flow bench you could test this for yourself) but like everything else, the valve size decision is based on money. Scrilla. Cabbage. Whatever you want to call it. The decision is mostly financially driven.
Just like why the small block Chrysler has a what? 1.68ish valve spring installed height. Because a shorter spring costs less MONEY. Which means you can what? You use a shorter valve. And a shorter valve costs LESS MONEY.
I hate to break it to you but most of the decisions on the architecture and geometry of these engines is financially and NOT performance driven.
In high school I build a 318 for a guy from another school. It went together with a Strip Dominator, Hooker 5204 headers, a DC 284/.484 cam and 360 heads. Yes, I gave up compression to get port and valve size.
The guy made far more than the cost of the engines going out and taking money from big block guys and dullards.
Could we have used 2.02 heads? Yes? Why didn’t we? COST. We were in high school. We didn’t want to blow our wad on these things. We had girlfriends (expensive), we had beer to buy and other things to do. So we saved the money.
So the small valve, small port LIE needs to go away.
Again, if you had a flow bench you could test all this. You’d learn right quick that porting heads and intakes is nothing more than velocity management. You can have too much velocity and I see it quite often.
I PM’d Dan and wrote a few messages to him. I figured a few videos from Richard Hold we would clear a few things up as well as create more questions. I specifically sent him to the Fire section where Richard runs through displacement sizes of 320, 331, (IIRC) 347 & (IIRC) 393 with near stock cams to small street cams to pretty healthy cams that can be a real bruiser on the street for sure
During all of the testing, he runs through many heads from many companies in various size cc runners and such. It’s very informative and can be eye opening if not overwhelming to a new guy, so slow digestion of this should be done. Just a few videos at a time to view and think about.
It’s funny because nothing is in stone. The variations are darn nearly infinite. Certainly head spinning.
When I watch these videos, I try and play a little guessing game in my head as quick as I can before he shows the results of the run. While I have to state I’m not the most accurate by far, I’m not really surprised (being in the ball park of the combo) but often certainly do pick something up.
I told Dan to watch a few at a time and think about it.
I suggest the same for everyone else no matter how seasoned you think or actual are.
The take away from everything Richard does on the heads should help anyone in their next head choice. For me, even before I seen Richard’s channel or the vine masters is, well, Freiburger says exactly what I say, “Get the best cylinder head you can afford!”
For me, it was the TF-190’s on my wife’s 11-1 360cid with a hydraulic roller cam. I’ll end this with lift the valve as high and as much as the head flows good and maybe a tad more since it’ll see that value twice. It’s not always needed but you’re taking the max advantage you can on the head this way and why not?