Intake manifold for turbo applications

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Hello all, this is my first post on this site, so I'll try not to look stupid.
I am currently trying to design a new intake manifold for a turbo 1.6L engine. I have never attempted to this before, but I have a few ideas in mind, and would like some feedback. First, I could use a D-shape pipe for a plenum, and just straight pipe it to the head. My second thought is to use a turbo exhaust manifold, which has even length pipes to each cylinder, and modify it to fit the intake.
The thing I am wondering is why every other turbo car uses a plenum style intake instead of a tube design. I understand that the plenum allows a build up of a pressure, but does it then not take longer to pressure up? If you used a header type intake, would it spool up extreemely then? Would you lose top end power because of a volume issue, or would the better, more even flow of air compensate for this.
Sorry the post is so long, hope that someone has an answer or two for me.

 

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Does anyone have any help for me? Perhaps someone with fluid mechanics knowledge.

 

[ray b]

just an old hot rodder
but the intake is less important on a turbo
as the pressure is a great equalizer and if you want more flow crank up the boost
pipe size and shape goes away with pressure
ext both before and after the turbo is where the gains are to be made
inc the whole ext pipe system you can't go too big there

 

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Thanks for the reply, but why do all of the aftermarket intakes use a large plenum and then use runners of of that? I was reading another post on this site that said that the larger the plenum, the longer the lag, and the shorter the runners, the more torque and less top end you get and vise versa. Just wondering why?