At 10 psi I have logged MAF readings of 57.49 at somewhere near 5400 rpm. According to that chart I am close to 12 psi but only see 10 on my gauge. I don't think I am getting 600 fhp either. I may be getting 500 fhp and 375 rwhp at a guess.

According to Garrett you can calculate your MAF in lb/min from your HP goal.

Wa = HP * A/F * BSFC/60
Wa = Airflow(actual) in lb/min
HP = Horsepower Goal
A/F = Required Air/Fuel Ratio to run safely
BSFC = Brake Specific Fuel Consumption converted from lb/hr to lb/min = .5 to .6 so use .55 = lb/(Hp*hr)

Wa = 600fwhp * 12 * .55/60 = 66 lb/min or 33 lb/min per side

Required manifold pressure to meet your HP Goal.

MAP(req) = Wa*R*(460+ Tm) / VE*N/2*Vd

MAP(req) = Manifold Absolute Pressure in PSIa required to meet HP Target
Wa = Airflow(actual)
R = Gas Constant = 639.6
Tm = Intake Manifold Temperature (*F) say 130*F
VE = Volumetric Efficiency (use 90%)
N = Engine Speed (RPM)
Vd = Engine Displacement (CI) = Litres * 61.02
DeltaP(loss) = pressure loss in intake piping and IC

MAP(req) = 33*639.6*(460+130) / .9*6000/2*186
MAP(req) = 12453012/494100 = 25.20 psia
BOOST = 25.20 - 14.7 psia(Pressure at sea level) = 10.5psia

P2c = MAP(req) + deltaP(loss) = 25.2 + ?? say 2.0 psia = 27.2 psia
P1c = Atmospheric pressure at sea level - P(loss) through air filter and piping to compressor say 0.5 psia
P1c = 14.7 - 0.5 = 14.2 psia

Boost = 27.2 psia - 14.2 psia = 13.0 psia

IIc = Pressure Ratio = P2c/P1c = 27.2/14.2 = 1.92

If you compare that to your compressor maps I think that you might find you need larger turbos. I am a newbee myself but it looks to me like you will need turbos that can flow 33 lb/min at a pressure ratio of 1.92 and stay inside the surge and choke line. The above calculations make several assumptions that may be open for further consideration.

 

So...the T04B "H Trim" turbo should do it then....

 

man I love all this technical discussion Good info guys!

On a side note: I sure hope both of you can make one of our private trackdays this year out in Cali(fontana), I'd love to whoop some of that turbo ***!

 

 

Why go with twins when all you wan't is 600bhp? A single turbo can easily and efficiently flow 66lb/min. Size the exhaust housing right and it won't lag at all. Twice the parts twice the problems when it comes to that power level IMO.

If you must go with twins though, take a look at twin 60-1's. Check out the map on that compared to the T04-H's. I think you'll like the 60-1's better, especially if you're going to up the boost, because I know you will.

 

Why do all the work when someone else has done it for you is my approach.

Good luck on the project.

 

The peak of 33 lb/min at a pressure ratio of 1.92 puts it right in the middle of the 74% island on the T04B H-3 map. I think that is way to close to the surge line. The peak should be closer to or at the choke line which would be 45 lb/min at a pressure ratio of 1.92. It looks to me that anything under 4000 rpm you will be to the left of the surge limit line.

It looks to me like the T04E 57 trim might actually be a better choice. Since the price is right they may be a good place to start. They look to me like they will spool up faster and not get into the surge line quite as much at lower rpms. At 3400 rpm you need 38 lb/min or 19 lb/min per side which appears to be close to the surge limit but still on the correct side of it.

The 60-1 also looks like it would work as well. Both the 60-1 and T04E 57 look a little on the large size to me for a twin turbo application. I am not sure what the real world results would be.

 

I understand.....sort of

Thanks for all of your input guys....especially you Mort !!!

Back to complicated mathmatics.....