what is enrichment?

could someone explain enrichment to gas to me?
thanks

[AlbinoMonkeyRat]

this might help get an idea of it, even though I think it doesn't adequately describe it:
http://www.andial.com/content/930/fuel_enrich.htm

also, know that the fuel injectors spit the air-fuel mixture in at a certain ratio, usually about 50/50 by volume. But when the ratio is altered, performance is changed.
Lean (more air than gas): better mileage, hotter combustion
Rich (more gas than air): worse mileage, more horsepower/torque

And I'm sure somebody can elaborate for better details, definitions, etc.

I hope this helps.

actually the fuel injectors only add fuel. also, the air/fuel ratio is closer to 12:1 on enrichment for power and 15:1 leaned out for best mileage.

^^ what he said, 12:1 is generally enrichment mode, which is usually only entered above 90% TPS And its primary function is not performance, while there is a slight gain, it is to keep the catalyst from overheating. Oh and 14.6:1 is where these cars usually operater, pending, not in enrichment of in some mode due to altitude or temperature.

How much more horsepower can you expect from changing the air to rich?