[Jim2]

Think back to the days of ITBs on carbureted applications, side draft/ down draft webers etc. At partial throttle openings you get a higher inlet charge velocity (down-stream of the butterfly) which gives more mid range torque due to ram effect of the charge, whereas a single throttle body at the end of a plenum sees the entire column of charge in the runner moving very slow when at low and mid power demands.

However, if you look at old aggresive race cars with big power (individual runner style) you will see very large diamerter butterflys, this was not only for accomodating a large choke, but also to diminish the restriction which is caused by the butterfly and shaft at WOT, but then catch 22 comes into play and mid range torque drops off due to the large runner and butterfly dia. The trick equipment used slide plate throttle bodies which eliminated the butterfly and shaft, but kept the throat diameter a bit tighter sustaining a higher inlet charge velocity.

To this day I remain surprised that this concept of an accerlerated charge works because a partially open butterfly seems like an extreame turbulence causing restriction, but it does works.

Get out your credit card and order those TWMs!

Jim

EDIT, I have never heard of a "downside to ITBs" when going turbo. Just a myth like lots of other crap out there.

Now for a myth rant with regards to aspirating the inlet ducting on a turbo application, get out a claculator and compute the inlet side volume using some rough diameters and tubing lengths, and say your intercooler is about 50% volume for the charge core, or heck, just use 100%. Now divide the pumping volume of your turbo engine's displacement and see how many revolutions (cycles) it takes to move one inlet charge volume, then calculate the amount of time it takes to move this inlet volume at say, 3000 rpm. I bet the reults will be 100ths, or perhaps 10ths of seconds, certainly less time than it takes to remove your foot from the gas pedal. end [myth rant]
Jim