OK, Russell, with all those cricket sounds you hear, I'll bite.
Understand I'm not a student of engine rebuilding and have none of the knowledge of some of our experts here, not in any order, such as Dr. Benz (Dan Caron); JA17 (Joe Alexander) or Stickandrudderman (Colin Ferns). But I suspect that any of those sources, along with others such as [once again] Mike Elias of Metric Motors in California, Gernold Nisius of SL Tech in Maine along with a host of others in UK and Germany might be able to open a dialog with you to answer your questions.
Years ago we had a hyped up 1966 Austin Mini Cooper S that had quite a few engine modifications. The prior owners neglected one essential item in the valve train: the rocker arms. Despite changing the camshaft, pistons, etc. he had left the original pressed steel rockers and once we got that engine tuned to optimal with proper carburetors, we started breaking these rocker arms. At that time, BMC did make upgrade kits for this A series 1275 engine, and we bought a set of forged rocker arms and problem solved. The bottom line on this is that, I believe, the entire valve train works together as a system. If you change one thing, you may need to change everything and "make it all match" In the case of the old Cooper, the goal was more HP and higher RPM. This was achieved...but it took some broken rocker arms to figure it all out, along with removing the leaky Weber 42DCOE and replacing it with 2 x 1.5" SU Carbs ex-MGB. These were pre internet days and there was a lot of trial and error. Tuning the SUs required a large set of needles and doing ¼ mile acceleration runs on a stretch of deserted highway.
You asked about "better steel" which infers that the OEM steel and valve springs are somehow inferior? I personally have not heard of (which doesn't mean a lot other than I've had my ears here for 20+ years) anyone trying to modify the valve train or head; usually they are trying to get it "back to right" which may require new valves, new springs, decking the head and other machine shop work. When my own engine was rebuilt by Metric 20 years ago, they found a small crack that needed welding.
In the case of our old Cooper, and also in the case of many American cars/engines, people are trying to get more HP and often greater RPM out of the engine without the engine self-destructing. In our Pagoda case, almost laughably, many people are trying to LOWER the RPMs, not raise them. At highway speeds in my Pagoda, I'm often turning a head numbing and deafening 4,000 RPM. Those with an overdrive 5 speed laugh at me as they turn 2,700 or so at the same speed. I try to keep mine to 4K on the highway. When all else is OK (i.e. my exhaust system isn't falling off!) my Pagoda has repeatedly cruised at 3500-4000 RPM all day as I've driven to events over the past 20 years.
I have not directly answered your question. But I hope one of the following happens:
1. I have a lot of information wrong, and those mentioned or other experts will come and correct my information and in the same response, answer yours.
2. I have a lot of information right, or directionally so, and those same experts will also weigh in here and again, in the process, answer your question(s).
3. I've given you some additional resources to try and contact directly.
In the spirit of these forums, do indeed report back with any findings you discover! Good luck!
