SAE40 Engine Oil (55Gal. Price: $300.00) 40WT. API-CF (Low Ash Content) oil that far exceeds the 1% ash content with a content of 0.78%.
Detroit engines have very specific requirements for engine oil:
1) use only SAE40 oil, no multigrade. If you're in an extreme northern climate you might use SAE30 in the cold of winter, but it's better to use a block heater to help keep the oil warm and use SAE40.
2) the oil must have a sulfated ash content of 1.0% or less, the more less the better. Any oil 1.0% or above does not meet the engine oil specs.