Speedmaster heads for SBM
Sure they will fit. But the 2.02" intake valve's and the bigger ports will hurt low end torque. It's been proven that smaller valve's along with good port work will give excellent results. A 318 will have to be spun at a higher rpm's in order to get the full benefit of the larger valve's and ports. I wish that a cylinder head company would offer a cylinder head especially for the 273 / 318, one that has 155 - 165 cc intake runners and 1.880" intake valve's and 1.600" exhaust valve's. Edelbrock has a cylinder head just for the small bore small block Chevy. A cylinder head that has good port velocity. The AFR165 heads for the sbf has 165cc intake runners and they have good port velocity. I believe that if they were to offer a cylinder like that that it would sell well as I've read on here countless times about guy's looking for good heads for their sbm. Sorry about high jacking this thread but I wanted to say what I thought and I'm probably wrong and some may disagree with me and I'm fine with that. Sometimes you have to create a demand.
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.