This one I saved for last, and for good reason. This is perhaps one of the best modifications that you can do for basically nothing. As you'll see in the dyno below, which is of my Integra LS motor in a 92 Civic hatchback, before and after: I got back almost 10ft-lbs of torque over the entire rev range. 10ft-lbs that was present in the engine when completely cool, but once at operating temperature was no longer available. This is good for about 0.2 seconds in the quarter mile in my particular vehicle - needless to say I'm very pleased with this modification.