Battery upgrade or not?

[Sacto S]

Is the original ('67 911S) battery/electrical system strong enough to keep up with the demands of H4's, MSD system, stereo, etc.? I have been told that it would be a good idea to go ahead and "upgrade" to a larger more modern battery. Is this necessary? I'm not thrilled about the idea of removing the old battery tray or modifying the original battery area. Is there anything I can do with my old smaller battery and system that would assist with the demands made by the added systems?

[Eric911S]

Hello: I would install a Oddesy battery. They are small in size but have lots of amps. They also won't spill since they are a dry cell type battery. I have used the 950 cranking amp one for years and am going to try the smaller I believe it is a 650 amp one on an AC'd car. These batteries work great for the track as well. They also work in Boxsters that are used for the track. Thanks Eric

[911pcars]

"They are small in size but have lots of amps."

The Odyssey battery is indeed light, but the cranking power of lightweight batteries is usually commensurate with their weight. Which is not to say the Odyssey isn't a good choice. If the ambient temperatures are fairly mild and the amperage requirements of factory and aftermarket accessories aren't too heavy, lightweight batteries should be fine.

The main objective of the battery is to crank the engine and to power accessories when the engine is OFF. When the engine is running, the alternator is the main source for electrical power and to recharge the battery. If the electrical load from add-on accessories exceeds the capacity of the current alternator, a higher rated alternator is probably in order.

I believe the early alternators have a charging capacity of around 65 amps. Does the sum of your accessories exceed this? With the exception of an audio power amp with unknown power specs, IMHO, the accessories you have shouldn't require any alternator or battery upgrades.

Sherwood

[Eric911S]

Hello: I forgot to mention that the early 911's to about 68 or so have a 35 amp alternator and the later ones are 55 amp. If you have the 35 amp alternator and want/need a larger 55 amp I have some rebuilt and will trade for the 35 amp. I live in a climate with no cold weather and no big radios in my cars so the small alternators work fine. The early Bosch alternators have a tag that tells you the amps of the unit. The Odyssey battery worked on a 3.2 911 engine with 11:1 compression in 40 degree weather, if that helps any. Thanks Eric

[Sacto S]

I just had the original alternator rebuilt. I failed to note the output at the time. Doh! I'll get in there and check it out.

Thanks!

Joe

[304065]

If you want an upgrade, get the sonnenschien as detailed in the below thread.

http://forums.pelicanparts.com/showt...ht=swb+battery

An Optima that doesn't fit is not an upgrade, it's a fire hazard.

The alternators are NOT interchangeable between years, they have different thicknesses that will require a different fan shroud. The voltage regulators are also different, you should not use a Bosch with a Marchal and vice versa because the excitation voltage is different.

If you must have more power the best option is the AASE alternator which is rated for 95 amps:

http://www.aasesales.com/alternators.html

Obviously this will require significant upgrades to much of your original wiring, in particular the cable between alternator and starter and the biggie between starter and the battery. Putting 1330 watts through a wire designed for 490 is asking for a fire.

If it were me, I would do a "load analysis" consisting of the following:

MSD at 7000 rpm. . . 7 amps * 14v = 98 watts
130W high beam H4 x 2 = 260W
25W x 4 RMS stereo = 100W

and so on . . . the above totals about 458 watts, doesn't include heat losses in the wires and high resistances in the 40 year old wiring, but it's using 93% of the electrical capacity of the car, which means that you're draining the battery as fast as the old alternator can fill it up, and you do NOT want that old alternator dancing as fast as it can. Something to think about when considering adding a bunch of heavy electrical accessories.

[NeunElf]

My 1965 911 has 100 Watt H4s (not that I use high beams much), an antique Permatune and a Blaupunk Frankfurt (not much output power, but it can't be very efficient, either). It does quite well on an ordinary Interstate 22NF battery.

If you're using power faster than your alternator can replace it, you will eventually draw the battery down, whether you have an Interstate, an Optima, or any other realistic battery.

The high tech batteries have a number of advantages, but they do not create electricity.

[Eric911S]

Hello: Bosch made two different amp alternators that will fit in the same early fan housing. How do I know? I have both Bosch type of alternators and they fit in the same housing. You don't want a 95 amp alternator on your little 2.0 engine. It takes power to run those big alternators. Also I'm not saying Optima it is the Odyssey battery. I would check to see what amp alternator you have then go from there. You could start the car up and turn everything on and check to see if you are getting full voltage or not. If that doesn't work just run the car and have fun. Thanks Eric

[jonnyw]

I had great luck removing my dual batteries and getting an Sealed Oddyssey battery. I put it in the smugglers box.

The original system was not quite as bright for me until I converted to a single battery. I have the same setup as you do. MSD H4's etc.

It even starts better with 1 battery in the cold weather.

Jon