Compression Ratios on Motorcycles and Octane Requirements > It is conventional wisdom and true that the higher the compression ratio, > the higher the octane rating required to avoid pre-ignition. It is not true > that all engines of the same compression ratio require the same octane > rating. Combustion chamber design of modern engines, especially 4 valve per > cylinder engines, improves the ignition and combustion characteristics > lowering the octane rating requirement. A Good Example of This: Jean's 600 Bandit. With an 11.3 to 1 compression, any of us with a memory of the Detroit big block days might assume that it would require something close to AvGas to run properly. Not so with the head design that Suzuki gave it - it runs perfectly on 87 octane. About the only time that motor will ping is if you slow it down to about 25 mph in 6th gear and crack the throttle wide open and hold it there. The old "rules" just don't necessarily hold true anymore with the well designed multi-valve heads where the shape controls the burn. rpw --- Bob Ward - Motorcyclist - COG #2936 - Bonney Lake, WA