Reformer-enhanced alcohol engine system. The engine system includes a spark-ignited alcohol engine having a compression ratio in the range of 13-15 and includes a turbocharger or supercharger operatively connected to the engine to provide a pressure boost of at least about 2.5 times atmospheric pressure to cylinders of the engine. A source of alcohol is provided for injection into the engine. A reformer is provided including a low-temperature reforming catalyst in a heat transfer relation with exhaust gas from the engine and arranged to receive alcohol from the alcohol source for reforming the alcohol into a hydrogen-rich gas. Means are provided for injecting the hydrogen-rich gas into the engine and a knock sensor detects knock in the engine. A fuel management control unit is provided which is responsive to the knock sensor to apportion the ratio of alcohol injected into the engine to hydrogen-rich gas injected into the engine. The engine of the invention can provide a 15-25% efficiency gain in a methanol-fueled spark ignition engine relative to a diesel engine in a typical drive cycle.