got the turbo PICS NOW>

[Doc Zaius]

Alright... here's my thoughts:



This is the compression map for a GT2056, 55 trim... probably the same or close to what you have. Now, if you're hoping to make 150 HP at the crank, and we assume a few things like air/fuel ratio of 12:1, and fuel consumption (BSFC) of 0.6, then your actual airflow will be about 18 lb/min. Depending on the actual air/fuel ratio or fuel consumption, this could actually be anywhere from about 16 lb/min to 20 lb/min.

Next, to figure out the Manifold Absolute Pressure, we take the airflow value of 18 lb/min, and a few other things:

• gas constant = 639.6
• intake manifold temp = 130 F (assumed)
• volumetric efficiency = 96% (assumed)
• engine speed = 6,400 RPM
• engine displacement = 1,500cc

Plug all that into a equation, and get a MAP of about 24, but could be anywhere from 21.5 to 26.6 or so. Subtract ambient air pressure (14.7 psi), and add a few psi for pressure loss due to piping and air filter restrictions, and you're looking at a pressure ratio of about 1.9 (could be 1.7 to about 2.1).

Whew!

Plotting 18 lb/min and 1.9 pressure ratio on the graph, and you're looking pretty good. Pretty far from the choke line on the right... and just off the biggest efficiency island at full RPM. If we replug in some numbers to find out airflow @ 3,000 RPM with the pressure ratio of 1.9, we get 8.5 lb/min, so just barely inside the surge line on the left.

So these are just the numbers... interpreting them is not my thing. It looks like this turbo would be good for high RPM operation, but might have a bit of lag. I don't know. But good luck... I'll be following this project with much anticipation!!

BTW, all these equations and stuff I learnt came from Garrett's website, and building an Excel spreadsheet to help play around with values.