turbos, VE's etc...

[Clive Apps Techno-Logicals 416 510 0020]

> 
> 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? 


yes it will skew it
also you will have  higer pumping losses at higer boost levels because
of the ability to flow in a port becoming restricted by desinty of the
air

if you have an estimated curve for the stock engine
and multiply this by the PR you will be close, but you want to richen up
slightly at the higer RPMs to prevent meltage

boost comes as a squared function of impeller speed
so the cruve will skew higher at the higher RPMs 
also since higer RPMs also mean more airflow it is closer to a cube function

so for ex>:
you have stock engine makes 10" vac 2000 rpm   8" 3000 6" 4000 4" 5000 2" 6000
you add a turbo and get these numbers 8" 2000  4" 3000 +4 4000 +12" 5000 +24" 6k
so you have increased airflow by 
6% 2000 13% 3000 33% 4000 53% 5000 80% 6000
so you need to add fuel to compensate for the extra air

Note: this does not take into account any expansion caused by heating
if your air temp jumps 150^ you will be actually reducing the numbers above
by * .74 to get the air mass

so you would add
4.5%, 10.5%, 24.5% 39.2% 59.2%  which would be approx = to the power increase
ie at 6000 RPM 24" =12lb boost = + 60% power
almost like real world results

you may want to go a little richer to protect parts and make a little more power
12.5-13:1 A/F is close to max power point
also allows margins to prevent meltage of parts
 
> 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!


you wont make 700 HP on 2.5" pipes
you should stay with the 3"
keep them straight for as long as possible
you can put a grille type diffuser befroe the bend to reduce the spiralling
something with 1cm boxes about 1cm deep would work OK and not cost too much 
airflow, maybe you can find a stainless grill from a florescent light fixture
it will have to be sianless of ceramic if you want it to live in the temps
involved

Clive