Batteries and Balance

[B Goode]

I searched the BBS for this, but couldn't find much conclusive -

About 8 years ago when my '73.5 911T was still on the road in spite of my inability to feed it with money, I found a nice cheap solution for replacing the two small but expensive batteries with one longer battery shoved sideways into the cavity beside the fuse panel. With higher cranking amps than the originals, I had no problems with power for the next few years (although I did have to replace my alternator eventually with an updated one with an internal regulator).

Currently, I am in the process of reassembling the front end of the car after an extensive rebuild. I would actually like to keep my one battery soulition for the sake of simplicity and I want to use the other battery cavity for storage. The question is - how much am I giving up in terms of balance? I never noticed much a difference before, but that was with worn out front everything (now replaced).

I won't be putting this car on a track, so I don't expect my handling demands to go beyond the normal (for a Porsche anyway).

[MikeBogue]

I would not think that you would sacrifice handling at all, as long as the overall battery weight is the same, or lowered. While you are going to a one battery system I would suggest that you rewire it to use only the passengers side battery as this will provide a better weight ballence when there is only a driver in the car.

[afterburn 549]

PC 680 is the only ans. 12 lbs and starts dwn to 30 deg.

[Grady Clay]

The original ’65 911 was so light in the front, particularly
with an almost empty gas tank, that the handling wasn’t
what Porsche wanted. Another issue was on bumps, the
suspension had nothing to react against.

Porsche attempted to solve this by adding two 20+# iron
weights inside the front corners of the bumper. I can just
imagine the engineering embarrassment having to add
pig-iron to a Porsche 911 to get it to handle properly.

In the parts manual Porsche refers to these pieces of iron
as “Bumper reinforcement front left” 901.505.911.00 and
as “Bumper reinforcement front right” 901.505.912.00 as
if we should look for some in the rear – Ha. It almost seems
as if the keeper of the part numbers wanted to rub it in by
assigning 911 and 912 part numbers.
"
"
© 1967 Dr. –Ing. h.c. F. Porsche K.G.

With the redesign for the LWB, Porsche used the two
batteries as “reaction mass” for front suspension bump.
This had the effect of increasing the polar moment
about the longitudinal (roll) axis. I can tell the difference
in handling.

One thing to keep in mind: this only works if the twin
batteries are properly clamped down tight with the
original straps.

By ’74, the 911 had gotten so heavy as to negate the
need for the reaction mass. The impact bumpers and
bumper shocks took the place.

Best,
Grady