"I would not jump to that conclusion. There are 8 cfm to be had between the stock exhaust flow of about 114 cfm and the theoretical maximum exhaust flow of 123 cfm with the 35 mm exhaust valve. If the ports were better, that gap should be diminished. 8 cfm is a lot even if it does not seem like much."
That flow is assuming a basically "perfect" port isn't it? Gains in port flow get smaller as you approach the ceiling-but maybe you're right. Either way I made no conclusions. It was just a suggestion. All I can speak from is my own experience having played with a few of them- that experience tells me that the port is different. Better, worse, I don't know. I just know it's different. That's what I see with my own eyes and grind with my own grinder.
Re 405/531 and turbo motors:
Where did you get that info? I'm quite certain b23et and some b230et had "big heads" but I'd call that all just speculation anyways- It's probably Volvo didn't develop the head with any specific ebr in mind- definitely not as a priority anyways.
"In short, I would say that the common 38/46 combination is a little short on the exhaust side. I would go at least 40 on the exhaust."
In the land of people without unlimited funds to spend melting drivetrains, the 38/46 represent a good improvement over stock at a good price. That's why I bought them. Besides, i'm confident they will support lots of power considering what the group a b21's made with stock sized ones.....
Re valves sizes and seats:
I know it's 90mm total diameter w/ siamesed seats... not sure what you can do in a boosted app with existing seats. I'll never bother to find out I don't think. the 46/38 combo is so affordable I'll never be able to justify anything fancier. Being that valveseat installation is beyond the ability of most- I'm sure the machine shop would advise on a per-project basis.
"Or do some more research on the intake to exhaust ratio theory."
It is valuable to me in that it gives an indication as to how the head will affect ebr- which is very important to me. Just part of the system though. the actual flow ratio needs to be measured against the whole system though which is where people misuse it imo. One needs to look at TOTAL intake pressure drop vs TOTAL exhaust side back pressure- from the air filter to the chamber, and then from the chamber to the end of the exhaust system.
"Sort of like turbo cam theory -- supposedly once you get EBR way down you don't really need a "turbo" cam with lots of lift and little overlap -- you can use a naturally aspirated cam with more overlap."
Well, that is a given, not even a "supposedly", because as ebr approaches ratios similar to those experienced in a normally aspirated engine, valve overlap and clyinder filling/scavenging act in a similar way as well. So yeah, definitely a fair assumption.
"I am going 16V next time -- maybe in a year. I have a long way to go still to reach the potential of the 8V motor that I have."
being that the record is well over 500hp, I'd say we all do. I think a guy needs to build one engine and build it right. We have both had failures due to not doing things right. My engine mated to that old m46 was a bad call. IMO your well built bottom and and nice valvetrain deserved proper engine management as you know. I think even relatively unmodified engines should make good numbers if they have the rest of the "support systems" taken care of. I have 80% of what I need to do the new engine and I'm trying to resist coblbing something together. I'm sure I could put something together and have fun with it until it turned itself into an expensive mistake, but good things come to those who wait I guess.