we have just been making carbon trumpet for our sports sedan and the work needed to get them strong and light is hugh. this is for just trumpets. making it out of carbon for a street car well coast you a $1000 in material at the minumum and this would be with little wasteage. it would take you a couple of weeks at minumum in labour this would be with long days. to make plugs and moulds. lots of sanding and bogging{lol} then spraying and glueing. much easier in aluminium. as to the design, short runners for top end power and longer for midrange. icould work it out if you gave me your combo. if its for forced induction dont worry about bellmouthing the plenum side as its only has gains in normal atmo engine. this is going on a race engine point of view, as it would help a lttle on the street for off boost performace as would longer intake runners. plenum should be double engine capacity. best setup for throttle-body is a staggered setup with a smaller doing the work down low. mick