Car enthusiasts are often more eager to improve gas mileage and keep maintenance costs low than to maximize performance hence choosing for the economy which
is quite natural. That means most cars are born with the equivalent of a stuffy nose. Below are the ways to increase horsepower

1. Upgrade to a free-flow aftermarket air filter.
* Buy a free-flow air filter that best fits your car.
* Open hood. Locate the air filter housing. which is the long pipe connecting the engine to a
square, plastic box.... READ MORE AT http://carz4mod.blogspot.com

remove all rubbish inside ur car...
driver keep fit...
dont fetch anyone else...
remove air conditioning system...
remove power steering system...

all the above is quite cost efficient, improve ur car horsepower and improve ur gas mileage...

Get the fat chick next to you out from your passenger seat.Put one thin beatiful ah lian next to you.That's called weight reduction.Pick up increases, mood also increase.hehe.
On a serious note just turn off your air con for night driving.feel a whee bit more power and no extra cost.