Hi ernesto,
The work a little like a slide trombone in that their length can be varied according to the needs of the engine throughout the rev range. Very basically, you will see an improvement in torque and horsepower at low revs if they are longer. At high revs the best torque and horsepower are produced with shorter inlet trumpet.
If you want you know more on an enthusiasts technical level there is a wicked site called AutoZine, check out the link below to their technical school below:
http://autozine.kyul.net/technical_scho ... _index.htm
If anyone else knows of any other good technical sights that can give you more depth and detail could they please post them?
