Viggen Turbo to Aero Turbo

     The Viggen and Aero turbos are the same turbos except for the turbine housing. The designation is TD04HL-15T – (5cm2 for the Viggen) or (6cm2 for the Aero). This last number indicates the smallest cross sectional area of the turbine housing. But basically it means a trade off, better spool up for the Viggen turbo but it chokes at the top end. The Aero turbo will produce more horsepower a the top end, sacrificing some spoolup.


     For installation of the Aero Turbo the main difference from the Viggen installation is the shape of the exhaust manifold exit. The stock circle needs to be ported out to an oval. Cutting disks or hand grinders work well but care must be taken not to remove too much material. The flange at the end of the exhaust header is thick, but the walls of the tubes are thin. This means the transition to the oval must be more abrupt than desired. Even so the improvement is obvious, the circle exit is the choking point of the stock manifold. The inside walls are rough and sharp lips disturb the airflow.


     I am not sure of the exact power increase the Aero turbo will provide but I am guessing 10-20 hp at least. I will be dyno’ing soon to know for sure. In the mean time I have done some data logging before and after the upgrade. The graph below shows a 3rd gear run for the Viggen and Aero turbos. Because of time discrepancies the graph cannot be used to compare spool up. The starting times have been changed to better show the pressure differences between both turbos. The run for the 5cm2 turbo was done at 78 F ambient and it was 84 F ambient for the 6cm2 turbo run.


With the Viggen turbo my Saab was producing 270 hp, which is very close to the limit of the stock fuel system. My last dyno showed an air/fuel ratio passing 12:1 near redline. To compensate for the added horsepower from the Aero turbo I’ve added a crushed fuel pressure regulator. The stock regulator is 3.0 bar and the crush regulator is 3.7 bar. This is within the 25 % range of a change in the fuel system that the ECU can handle.

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