smoothes the flow and prevents rust and heat buildup. jethot is the best. subframes would be my first, i wish i had done this sooner, if stiffens the frame and my ttops no longer leak or fit improperly. maf is a waste, if you are that concerned with maf, remove the screen and the huge wing inside the thing to get almose 100 cfm more flow. bilstein's rock, springs are good, hella headlamps are awesome.