That's one of those "it depends" kinda deals.
Cooling the air is always good. Cooler air is denser and puts more in the engine.
Are you cooling the fuel to avoid vapor lock? Then good deal.
Are you cooling the fuel to get more in the engine? A bigger jet will do that.
Are you trying to cure a detonation problem. Good deal.
Make more horsepower? Heating the fuel might do that. Honda experimented with heating the fuel on their F1 engine.
The hotter more energetic the molecules the faster they burn. The fuel has to be heated to vaporize and combine with the air molecules.
Too cool and the burn rate slows and it's still burning when the exhaust valve opens.
