[billwot]

Originally Posted by Tcoat

You have a total misunderstanding of something. There is no "rule" that they "must be able" to run on 87.
The manual does not say 91 minimum for "liability" reasons.
These are very high compression engines and need the knock resistance provided by higher octane fuel. This is not a matter of opinion or speculation but an engineering fact.
There are many older high compression engines that if you try to run 87 through them they will destroy themselves is no time since they do not have the ability to detect knock and adjust for it.
Being "able" to run on it and should be run on it are not the same thing.


You still have not provided the requested proof that there is a rule that engines must be designed to run on 87.