I recently disassembled a 91AC engine. When I removed the intake valve, I found four holes drilled in the top of the intake port that go through to the crankcase under the intake valve spring. Since I have never seen this on any other engine, I was wondering why they did it.
Thanks
Bill

They are using the pressure inside the valve cover to push additional fuel charge into the cylinder.

An then, on the overlap cycle, the valve train gets lubricated. Great idea.
Another reason why it is so important that there are no air leaks.
Are there any technical specifications available for these engines other than what is published in the owner guide?
Thanks
Bill

Not really. I think YS wants everyone to just be amazed by just how much soup these engines make, and even though there are those that are interested in the technical side of it, they are pretty close minded about discussing anything.