adverse handling
 

I am probably going to backdate an impact bumper car to pre impact style, and use fibreglass parts in the process

If I replace the bonnet and front bumpers plus rear bumpers in fibrglass, what does it do to the weight balance and the handling

I could change the engine lid too if this would help the weight distribution

just wondered
thanks

Keep in mind that you're backdating just as you said. So the handling won't be any worse then a long-hood car using the same sway bars and T-bars. To put it differently, it will most likely make your car feel more stiffly sprung. If there is any change you will most likely be able to tune it out just by changing to the same sway bars and or T-bars used in the earlier cars. Keep in mind that a lot of guys like a stiffer ride.

I also would expect that with the weight disappearing from the extremes of the car, that it will rotate a little better as a result of the reduction in the polor (polar?) moment. Kind of like a figure skater pulling her arms in while she is spinning.

Just calculate the wt. distribution twice - with the original parts and the ones you want to use.

Then calculate the "torque effect" on rotation by multiplying the wt. change times the distance from the center of gravity (CG). The CG is approx. behind the driver. Someone (Bill V.) thinks it is about in the same place for the earlier cars as for the 996. That's a reasonable assumption. There is a pic somewhere of the 996 with a triangle under it indicating the CG.

Bottom line - don't worry about the change.

Even though the short hood, impact bumpered cars are a few hundred pounds heavier, the torsion bar sizes didn't change very much. The rears went from 24.1 to 25 mm in '86 and the fronts stayed the same at 18.8 mm.

Thus, as you lose weight the ride will become a tad stiffer, about the same as an early 911 with stock suspension; which is to say, not firm enough for spirited driving. You'll probably want larger torsion bars sooner or later.

There are plenty of threads in the archives as to suggested sizes depending on your end use.

Hope this helps,
Sherwood