turbos, VE's etc...

[Andris Skulte]

I'm pretty close to putting the turbos onto the Camaro. I do have some
fuel/timing curves for the DFI, but they are all supercharged. How do
you figure out the VE of a turbo engine? I've got dyno and airflow
charts of the camaro when it was naturally aspirated, and figured out a
VE that way, but wouldn't adding a turbo skew the graph instead of just
raising it by the pressure ratio? 

Another question is about the downpipe sizing. I'm running twin T04E
.58AR turbos on a smallblock chevy. I plan on having 450 hp right off
the bat, and eventually up to 700 hp. I've heard different theories on
downpipe design. One was that you should increase the diameter right
after the turbo, to stop the spinning, and then make your 90 degree
turn. Someone mentioned that the spiraling exhasut gasses creat much
more backpressure in a bend than straight flowing gasses. Space is
pretty tight under the hood of the camaro, and the smaller diameter I
can safely (efficiently use) the better. The turbo outlet has a 3"
opening, and I was planning on using 2.25 or 2.5" pipes max. Is this
concept a big deal, or can I just neck it down right outside the turbos?
Thanks for the insights!

Andris

PS-I checked the archives, but there wasn't anything listed for the
exhasut...