I am not sure, but I think at least one of the reasons to why this keeps popping up every 10 years is that people forget the simple basics around ignition and flame propagandation. Now, in the older days when Berg senior advokated this his main goal was to increase fuel efficiency, decrease the risk of detonation and keep "as much power as possible" all by keeping it simple. He did it with the knowledge that was available at the time and to an extend his own findings. It is correct that a low compression Semi Hemiéd engine will run "cold" under cruise, but as soon as you start using the power over longer periods of time the cylinder head temperatures will rise, to the point of HOT. There is one simple reason to this. In a SH head you need a lot of timing advance to make the combustion complete before approx 20 degrees ATDC.. Back in the days (and to a certain extend even now) the general means of ignition is a simple 009 distributor. So what he/they did was simply to advance the distributor to some 36-38 degrees BTDC in order to get a reasonably completed burn on cruise. Here´s the problem: 36-38 degrees triming is WAY too much under full load. So in order to compensate for that Berg reduced the CR even further resulting in a "revy" engine with no guts.
Now, even back then they had VW´s own SVDA distributors, but they were just a POS distributor that no one understood or cared about, except maybe Joe Karcey. They never went into exploring the options with them. They just went the simple and in efficient way, because among other things it sold parts.
The reason why SH doesnt work well in "our" engines is that when you need say 36 degrees timing to get a complete burn you ALSO expose the cylinderheads and the pistons for a lot of heat for a relatively long time. Lets do a simple calculation. Lets take 3500 rpms and 36 degrees timing versus a more normal 32 degree under load. That results in the heads and pistons being exposed to 1940 degrees MORE duration to combustion pr minute, or 1,1 Ms per combustion. The next thing is the increased pumping loss which is a direct power and efficiency loss.
One of the Berg brothers is advokating a modernized version of the SH heads. So is Joel Mohr. They do get a fair amount of power out of these engines. Not over the top, but absolutely fair. I was never able to see exactly what they do, but I think I have a pretty good idea though.
On the other hand. If you instead made the chambers as burn efficient as possible, and at the same time made sure that the incoming mix was/is properly atomized, AND of course have a proper relation between intake and exhaust, you can go high compression, BUT! not so high that you have to reduce timing to avoid detonation) use a slightly recurved SVDA distributor or go with one of the simpler 2D programmable distributors like the 123 bluetooth, USB or similar and have the option of advancing the timing and go lean cruise and still have proper timing under load.
This will give you an engine that is equally efficient (if not more) on cruise and will have some umph when you step on the loud pedal, - AND at the same time run cooler under load.
Back in the days VW type 1 bus engines typically had a max timing of 28-29 degrees under load and 36-38 on cruise. The later somewhat revised CT engine which had a very hard life in the T25´s had a slightly different and in fact a tad more efficient combustion chamber. They still had 28-29 under load but a whopping 40 degrees on cruise which worked due to the lean circuit on the carb. (Remember, at lean mixture takes longer time to burn as a stoich mix, just as well as a rich mixture takes longer to burn.
The next thing we can do much better today is spark quality. The wimpy blue Bosch which have sadly become the industry standard simply does not cut it. you need better if you want a proper burn. You want a coil that can handle at least a 0,85 mm plug gap. 1 mm is great. You want a fast and powerfull spark that can get the burn started the moment the spark occurs, not some 4-5 degrees later.
A good cylinderhead with a good "bath tub" chamber along with a decent midrange ignition system can easily be optimized to have peak power at 30 degrees BTDC. The really good heads can go as low as 27-28 degrees. On an optimized 1600 engine the mere optimization of ignition timing from 32 to 28 can easily result in + 3 hp. That is 3 hp LESS pumping loss and some 1,1 - 1,3 Ms LESS combustion exposure to the heads and pistons, meaning a MORE efficient engine.
Now some people will come forward and say "Well my old 30 hp is doing great fuel efficiency and teperature wise, also on the Autobahn. Yes, and the answer to that is simple. Bore, CR and limiting performance with the intake. with the small 77 mm bore and the SH type chamber the burn is so relatively soon completed that it doesnt matter much. The larger the bore the worse the problem.
Look at it from another angle. The Dodge Wildcat, Hellcat etc engines have Hemi heads on a 105 mm bore. It works, and reasonably well by all means. You know why? They have twin plugs, one on each side of the chamber. In a more modern engine with roof shaped chambers which more or less work as a hemi shape there is one simple reason to why it works and works well. That is plug location. The plug is right smack in the middle. What more can you ask.
I could explain it in more details with a more scientific approach, but it would be less understandable for most. But I hope this helps in understanding the subject.
Now someone can translate to German
