PROFESSIONAL MOTORSPORT
SIMULATION SOFTWARE
Limited capacity causes test for overall performance
In the original GrandAm, there were different type of engines competing with each other. Pontiac, Ford, BMW, Lexus and the Porsche. 2 valve V8's competing with 4 valve V8's. The exceptional engine was the flat 6 Porsche out of the 996 RSR.
Due to the small capacity compared to the V8's, it ran unrestricted. Although certain details are not known, this engine configuration provides an interesting opportunity to test the engine simulation, because we know it was a competitive engine at that time and we know the power output of the rival engines.
Bore x Stroke:
Compression ratio:
Mechanical Losses:
102 x 76.4 [mm] (6 Cylinder)
13.5 : 1
0.8 [Bar]
Intake Valves:
Exhaust Valves:
2 x 40 [mm]
2 x 35 [mm]
Inlet Camshaft :
Exhaust Camshaft :
266 [mm] (@ 1 [mm] lift)
248 [mm] (@ 1 [mm] lift)
Intake runner:
Primary exhaust:
300 x 50 [mm]
500 x 44 [mm]
Rival engines delivered 520 [Hp], but wider powerband
Rival engine produced between 510 and 520 [Hp], albeit with a wider powerband. So if the Porsche produced the power as shown above, it would certainly be competitive.
Add the low centre of gravity of the engine and one can understand that this engine was an interesting option. It was an engine which caused a lot of policing, because it was so different. Looking at the 'possible' power output, one could understand why.
Good test for the poppet valve resistance model
In order to fill the (large) cylinders at high revs, the duration of the camshafts need to be long.
This means that at low revs, there is a lot of back flow over the intakes valves into the intake manifold, strongly reducing the fill rate as can be seen in the figure.