W2 valve size recommendations
If it was me (most people are thankful they aren’t me) I would spend some time looking at the exhaust side very close. I haven’t done it yet because I haven’t had the time, but I will when I get the chance. Anyway, I think a 1.600 valve is too big for that port. I’m pretty sure (just from doing a bunch of this stuff but this is still a working theory) that a 1.550 exhaust valve can be used with 45* seat with a bowl of 87-88% and still fit most of the radius under the 45. I have for a long time now stopped doing much work to the exhaust port, because it’s about air speed and shape, and not about cross section like the intake side.
You can keep grinding on the exhaust port and it will flow more on the bench. You can keep adding valve size to the exhaust and it will flow more. Hell, there was a time when every BBC I did got a 1.94 exhaust valve! That’s HUGE. Way too big and it’s a power killer. At last check (it’s hard to keep up with some of this stuff, people don’t tell you everything because it costs so much to learn, people flat lie) Pro Stock is only using a 1.800 exhaust valve.
I believe if you run a 50* seat you can fit a 1.500 exhaust in there. I haven’t proofed that yet, but I think I can, with a 95-96% bowl, still get the radius under the 50 and get a nice top cut on there. IMO, the smallest exhaust valve you can fit with your choice of valve job is the best thing you can do for the exhaust side. Minimal change of cross section, very limited port enlargement (the less the better). That’s my thoughts on W2 exhaust sizing. It’s a very good port (even in 2020 it still humbles many exhaust ports of today) so do the least amount of valve and keep the port as small as you possible can. Air speed is your friend here. Clean, quiet air speed and don’t worry about what the flow bench says for a number.
The intake side is different. While the W2 port is big, it was developed for small displacement engines (especially by today’s displacement sizes) it won’t support a valve as big as most guys want to use. The bigger the valve, the bigger the cross section to feed it. I’ve run 2.100 intake valves in the W2 and W5 because they will fit. But never again unless I’m porting for maximum cross section, which on a W2 is rectangle and that’s a massive amount of grinding. And that sucks buttermilk. And the W5 is intentionally small, but at least it’s not cast iron.
If you are going to use a 45* seat, I’d use a 2.08 valve and blend it off under the bottom cut. If it’s a early casting, I had a 45* cutter that I only used on low port angle, shallow valve angle ports (18* or less) with 4 angles that always out powered everything else. Today or tomorrow I have to go by the shop and I’ll get the cutter number and post it in case anyone cares.
If you are up for using a 50* seat on the intake, I’d stay with a 2.055 valve. The 50* is so far ahead of the 45 stuff it’s really not even a thought for me to do a 50 on anything I can. The shape of the 50 is so much better than the 45 it’s not even in the same league as the 50. For years everyone wrote about shape, shape shape and not size, and yet many of them are still using a 45, which doesn’t have the shape of a 50. And shape is what it’s all about.
If you are going to stick with a 45, I’d still consider the 2.055 because as big as the W2 port is, it’s hard to feed a valve much bigger than that on a stock W2 port. That’s why you see the port break over at .550-.600 lift. The port can support all that valve area. Bowl to seat approach is another reason for break over, but you live with that.
As displacement/RPM goes up, cross section needs to get bigger. Then it’s a real bugger to get enough port to feed the RPM. And then you run out of intake manifold.
A fully ported W2 with a 2.100 valve and a tunnel ram struggled to make power at 8500 on 340 inches. More cam would move the power curve up, but the car was slower, because it lost in the gear change.
Just my random thoughts.
