Decreased percentages of nitro richen the racing engine. It would seem that the engine would be less prone to detonation from the enrichment. However, according to Hutchison Racing Engines, Sacramento, CA, USA, that may not be the case. When you decrease the percentage of nitro increasing the percentage of methanol, the spark advance may need to be retarded. The increased methanol in many setups is less tolerant to spark advance. A reduction in spark advance is often necessary to avoid detonation.