Cold air is denser. Meaning your air and fuel mixture is more potent than normal. This is the same principle behind supercharging, turbo charging (especially with intercoolers), Nitrous Oxide injection, etc. You force feed more air into the engine for power or in a way make the air more dense. Some use carbon dioxide to cool the air before entering the engine. Carbon dioxide is very cold. Some use water injection for the same purpose.
A misconception on octane boosters. Octane boosters will increase octane numbers of fuel if you have bought a low octane fuel due to inavailability of high octane. If you have high octane already, the increase would be negligible and unecessary. You are just wasting money. Octane numbers of gas is the level of anti-knock properties of fuel and nothing more. Rule of thumb is just to use the proper fuel for your engine. Using higher octane gas will just make oil companies and additives companies richer. Racing cars, exotic cars use high octane not because its needed for speed. They need high octane because the engines are high compression engines. Using lower octane will result to knock or detonation and the car will not achieve optimum power.
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