Do the AWD 996 help an unbalanced PMI when turning?

 

Good discussion!

Bleu, thanks for the intelligent input. How about a carbon fibre hood?
I believe you can save about 30lbs???? How does this fit into the scheme
of things for track events?

MK

 

Well, there is a couple of questions buried here. First, does AWD hurt the PMI? Second does AWD help or hurt turning?

First, the AWD stuff is heavy, low and forward of the Cg. That increases the PMI which makes the car harder to rotate and hard to stop rotating once it starts. It is low which helps lower the cg which translates into good grip characteristics for chassis dynamics.

Second, AWD (all else being equal) locks the wheels to the engine just like the rear wheels. At 100% grip (e.g. a long sweeper turn on the track) the 2WD car has the front wheels devoting all grip to turning. The AWD car, if you accellerate at 20% grip for acceleration, can only give 80% to turning. Try to accelerate like the GT3 and you will create an understeer condition. Therefore, in laymans terms, the AWD car will tend to understeer more than a RWD car, all else being equal.

 

There are three parts to this one. BLUF: its a good thing but not the absolute best place to lose weight for the track.

First, overall weight loss. The overall wieght loss reduces the denominator in the calculation of how many G's your car can make in a turn. Not significantly (i.e. a small cross wind would easily offset this small of a gain) but it does exist. When you add this up over the entire lap you should see a small improvment in lap times, all else being equal.

Second, it does reduce PMI. Which would tend to make the car slightly more responsive in turn in and to a lesser degree in Mid-turn.

Third, it removes weight from the front tires which we have already noted (though we perhaps haven't directly stated) are already lacking grip in mid turn and tend toward understeer. This wieght loss above the front axle, expands this tendency which would tend to raise lap times.

A very small fourth part, is that you are also lowering your Cg. This improves, as we stated above, you chassis dynamics in that less weight will shift under load.

Overall, changing the hood (as long as it doesn't change the areodynamics at all!) should improve lap times but only very small amount. IMO