Holiday Preview Mod

Physics ReadMe

The HPM is a set of four Porsches from the late 60s, the 911 in 2 litre and 2.2 litre form, the 914/6-GT, the 906 "Carrerea 6" and the 910 prototype which was derived from it.

Engines -

All these cars have versions of the 6-cylinder boxer engine originally released in the first 911. The 2 litre 911 has 200 hp and shares this engine with the 914, plus there are 210 hp and 230 hp versions of the 2.2 litre engine in 911s. The 906 is the "customer car" version homologated as a sports car and has 210 hp from it's carburetted DOHC 2 litre engine. The 910 is the 6-cylinder version with 220 hp from the injected version of the engine from the 906. Engine files were based on data charts published in Paul Frere's book "The Racing Porsches".

Chassis -

The A- and B-Series 911 has McPherson strut front suspension and semi-trailing arms at the rear. The 914 is a variant of the same layout. The rF version of the chassis for these cars has an emulation of the strut suspension and a rearrangement of rF-style double-wishbones at the rear to function as the semi-trailing arms. The result is interesting as the overhanging mass of the engine in the 911 translates into a car which has more oversteer than the mid-engined 914, and has slightly slower on-track responses due to the relatively higher inertias. As you would expect, the characteristic strong oversteer is manageable for a skilled driver but one must pay attention. The result is that the slightly lighter and more agile 914 will mix it with the more powerful mid-range 911s.

The 906 and 910 are very similar under the skin. The 910 was derivative of the 906 with smaller wheels, wider tyres, a bit less weight and a bit less drag. Both cars are relatively conventional prototype/sports-racing cars of their era with unequal length double wishbones front and rear. Porsche believed in allowing racing cars cars to stick to the road by enabling reasonable wheel movement. They did this by making suspensions which were somewhat softer than some of their competition - a leaf out of Lotus' book. So these cars are not rock-hard to ride in and respond to subtle steering and throttle input.

These cars should be pleasant to drive with standard rF force-feedback or with the RealFeel plugin enabled. The MaxForceAtSteeringRack= value in the RealFeelPlugin.ini file should be set to negative for the 906 and 910.

Drivetrain -

We found a comprehensive set of actual Porsche ratios for these cars so there are plenty of options avaliable. The default gearing for each car is set for LeMans where the ratios were published for that track, so they are quite long-legged in standard form. For tighter tracks, the final drive ratio may be increased in the garage, which will increase acceleration at lower speeds at the expense of top speed.


I enjoyed developing the physics for these cars. I hope you enjoy driving them as well.

Bristow 
February 2008
