I'm sure he already knows what he's doing (he IS a 60* turbo pioneer after all... ) But I found this article and found it rather informative (especially the math and formulas).
http://www.autospeed.com/cms/article.html?&A=0122
The plenum should be about 80% of the displacement of the engine.....WTF was GM thinking when they made our intakes???!!!

 

In maximum boost they say:
The plenum volume should be a function of engine displacement-in general 50-70%.
On a side note it also says that the plenum should be several times the size of a cylinder.
I have herd of some plenums being the size of the engine or more.
This is strange, How build and mod SBC V-8 cylinder heads says that Al heads are best for turbo but Iron heads make more power. I'll keep my iron heads.

 

What was GM thinking? That they needed to design an intake for the V6's that would fit a variety of vehicle applications- maximum horsepower wasn't the goat!

 

Eric's got it right, as far as GM's thinking. They were looking for maximum torque, and they did it!

That was a good little article... 80% plenum? That's a bit on the high side for me

 

Well as far as my motor goes, it's not even 10% the displacement. They used that intake because it fit under the hood (it's only used on F-body cars FYI ). It had nothing to do with power delivery, or generating max torque. Intake design doesn't have that big an effect on turbo applications (unless you're losing boost after the TB).

 

Just FYI: The intake on the F-Body 2.8L and 3.1L V6 engines is most commonly found under an F-Body hood, however, I've seen it on a few other GM cars. I'm pretty sure the Fieros used a version with just a different angle on the throttle-body neck, and I've seen this intake design on some front-wheel drive GM cars at the local wrecking yard. I think it was a 2.8L Cavalier perhaps, I can't remember for sure...

 

Not the same though, lol. The lower runners are different lengths, the plenums are shaped differently, even the throttle body designs are different. I have a few FWD 2.8L intakes at the shop, as well as an upper manifold for a Fiero. The design used on the RWD F-body is F-body only. The FWD motors, while of the same displacement, were quite different from our RWD counterparts.

 

The fiero uses the same lower and middle plenum with a different upper. The middle is how ever turned around backwards. The arrow that should point towards the front of the motor must be turned toward the back.