|
|
BMW was smart in that they placed the battery on E30 performance models in the trunk, instead of in the engine compartment. Why was this smart? Because the stock battery weighs over 40 lbs and the last thing our cars need is another 40 lbs up front. However, due to the fact that the trunk still has to be a useful place to put stuff (on a car sold to the general populace) BMW had to tuck it into a recess near the very back of the car. This is fine from a standpoint of static weight distribution, as it shifts more weight to the rear wheels, which is apparent if the car is sitting on corner weighting scales. But having this much weight hung way out past the rear wheels has a negative effect on the "dynamic" weight distribution (i.e. the polar moment of inertia). Unfortunately this effect will never show up on the scales, it is only apparent to the driver on the track. |
| I recently discovered a partial solution to this problem in the form of a smaller and lighter Interstate . battery. It is still of lead/acid design, it is not a gell-cell like the Optima brand. But Interstate makes a kit to adapt the BMW vent tube to its batteries. The smaller battery is 8.75" long, vs. the stock BMW battery which is 10.75" long. |
The part number for the smaller Interstate battery is:
p/n MT-47 -B1 The battery cost me $100. It weighs 31.0 lbs compared to 42.5 lbs for the stock battery. weight saved = 11.5 lbs This might not seem like a lot of weight in an absolute sense, but one has to consider that it is being removed from one of the corners of the car. This is always advantageous to handling. The factory battery tray needed a new hole drilled in order that the smaller Interstate battery could still be secured with the original clamp. This was easily achieved as is shown in the photo. |
This is the Interstate vent kit which allows their batteries to function with the BMW factory vent tube. Note that this smaller battery provides less cranking amps than the standard battery (in this case 590 CCA "cold cranking amps" and 740 CA "cranking amps"). It is therefore not recommended for people drawing a lot of electrical current in their M3's (big stereos etc.) It will also be less able to turn over the engine in cold weather. Here in Southern California that is not a problem. Keep the limitations of a smaller battery in mind if considering a swap of this kind. There's no free lunch - right? |
|
|