Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
I have a reference written by the designer, Ryoichi Nakagawa, that I am sure says that the original design was intended for 100 octane fuel, but with the start of the war, the engine had to be modified to run off 92 octane fuel. The low quality of the available oil was another issue. Unfortunately, the document seems to be buried amonst others.
Robert
Hi Shinpachi!Addition...
Homare was began to design even before the war at Pacific started and as it was prolonged in 1942 finished in 1943 Japanese could assume that they could assert their outer defending perimeter. This became doubt only in the end of 1943Sounds like the Japanese assumed that fuel quality would improve over time, and design was started on that basis. They likely assumed that by the time the Homare would be entering service, 100 octane fuel would be available. The reality was not nearly as good.