ORIGINAL: foxy42
Engines are for tracks. They are usually either top end (for sweeping tracks) or bottom end (for short technical tracks). To a degree you can alter an engine's characteristics by using a pipe that induces the opposite effect of the engines natural powerband, though this can be risky, sometimes annihilating the power band of the engine completely. It's best to stick to combinations that are known to work. Example, you can have a v-spec (a top end motor) and put a low end pipe on it order to give it more punch, however, this does not always turn out to be the effect, you can easily ruin top and botom by doing this. It's often better to match an engine with it's pipe, a low end engine and a low end pipe. Generally speaking, though this is not a hard rule, the more ports, the more top end, the less ports, the more torquey, so basically, you need to know where you are going to race, and choose an appropriate engine for the track. My S5 was cheaper than your v-spec, but I'll rape you round my local short technical track.
I agreee with this.
Its usually better to get a pipe to match the engine, then alter the gearing as you are playing to the strengths of the engine.
For example if you have a torquey engine, get a pipe to enhance that feature of the engine then gear it taller. The car will then have more speed but you will only lose uncontrollable low end power.
Of course the other way can work but the negine will never be performing as well as it could.