MATT - I wouldn't say running higher than 87 octane gas in a working CC is a waste of money. These little Kohlers being air-cooled run hotter that typical water cooled engines, especially when worked hard like mowing tall grass on hot days. And the fact they have simple carbs with unsophisticated fuel curves means they don't enjoy the automatic fuel/air mixture control of today's EFI car engines with O2 & knock monitoring just makes a conservative tune on the engine more critcal.
The flat head combustion chamber in a Kohler is VERY much not suited to suppressing detonation, has very hot spots, so using a higher octane gasoline which resists detonation can prolong engine life. Pinging and detonation are not really the same thing, but the resulting high cylinder pressures result in the same problems, everything from blown head gaskets, crushed ring lands on pistons, broken rings, burned exh. valves & seats, accelerated rod bearing wear, etc. Rev. Bob even had Ken weld up a Kohler head that burned out between the intake & exh. valve years ago. Maybe Ken or Kraig can post the picture but it looked like someone torched a trench across the sealing surface with an acetylene torch.
Gasoline has to go thru chemical reactions in the cylinder before it "burns", and the octane rating is inversely relative to the speed the gas formulation allows those reactions to take place, higher octane number equals slower reactions which means it "burns" slower and won't detonate as readily.
If your tractor just idles around in parades, then yes, 87 octane will suffice, your not building ANY cyl. pressure or heat. But if your mowing foot tall grass on a 90 deg. day things get HOT in a hurry. My Onan burns a gallon/hour mowing, the ten cents/hour extra for a premium non-ethanol blend gas doesn't add up to much by the end of the summer.
I've had MANY conversations with many people about gasoline (I actually prefer diesel engines but....) Wyatt Compton, Don Vogt, Dave Kirk to name a few. Maximum engine efficiency is achieved right at the point of detonation for the fuel being burned. We ALL agree on that fact. But the problem is knowing when we're getting CLOSE to that point of detonation and it's effects on expensive engne parts. That's why I run a higher than 87 octane gas. My local Kwik-Trip sells a 91 octane with no ethanol specifically recommended for air cooled engines. And when I run it in higher output engines like my K321 in my CC 72 I blend in 104 octane leaded race gas.
Here's another good website with gasoline info, I printed the WHOLE thing off several years ago, explains a LOT about what gasoline actually is and does.
http://www.faqs.org/faqs/autos/gasoline-faq/part1/
The links to parts 2 thru 4 are at the bottom.
