Batteries.

Most of the cars in Spec Boxster run an Odyssey Extreme battery. They work great and weigh quite a bit less than a standard full size battery.

Well, they work great until they don't. Everything will be fine and then the battery will be dead as a doornail without any warning or hint of running down. This has happened twice - one time at the track and Brad Roberts had to R/R the battery in 5 mins with me suited up in the car so I could make a race.

The last thing that I need is more stress or something else to worry about at the track. So, now I treat the battery as a standard maintenance item and replace it every 12-18 months (around $150).

http://i1114.photobucket.com/albums/...psbyoclnpy.jpg

http://i1114.photobucket.com/albums/...psjaho2joy.jpg

Parasitic power draw.

I typically don't drive the Boxster very often in between racing events so it can sit for up to 60 days without being driven. I've never used a battery tender and so I have always worried a little that the battery might run down while sitting for that long.

So, this evening I decided to figure out how long the battery should maintain enough charge to start the car.

I started by measuring the parasitic draw on the battery by placing a multimeter in series with the battery negative terminal (disconnect neg battery cable and place the positive probe on the neg battery terminal and the negative probe on the neg battery cable). This will measure the amount of current being drawn by the car. Car should be off with key removed and doors closed and so on - just like it would be if it were parked and locked.

I measured around 2mA and converted this to 0.002 Amps (x1000)

Then I looked up the "C10" capacity of my battery online which was 27Ah (amp hours). C10 means the "10-hour rating". Then I multiplied the 27Ah capacity by 30% to get 8.1Ah. This is how much battery capacity could be used by the car over time and still leave 70% of the battery capacity to ensure that the car will start.

Last, I divided 8.1 Ah of capacity by 0.002A to get 4,050 hours. This is how long it will take the car to draw down 30% of the battery capacity. Then I divided 4,050 hours by 24 hour/day to get 169 days.

Even if I am wrong by a factor of 100% (due to battery capacity variation with temperature, age of battery, poor battery cable resistance, etc), the battery should still start the car even after 84 days (169 divided by 2).

This is consistent with my experience that the car has always started in between events of up to 60 days.

Important Note: I measured 2mA for a Boxster that has been stripped of most electronic components. The only components in the car that might use power are the ECU and immobilizer. Thus, I would expect this value to be much higher for a stock Boxster.

And yes, this is what I do in my spare time after getting home from a 10-hour work day. :)

My God... You lost me at, "I started by measuring the parasitic draw". Just get a Battery Tender and hook her up!!

That's a huge battery for a Spec Box. It weighs over 26lbs, puts weight high up in a bad spot. Most guys in TX & CO run a DEKA ETX14 or ETX12 which can be bought for $60 and weigh 12 or 10lbs respectively.

Do yourself a favor and take this opportunity to save 16lbs of weight and some cash.

Edit: Pull the cutoff switch when you park the car and you never have to worry about a dead battery.

You are correct.

However, because this is still a street legal car and I drive it to events, it needs to start reliably (as in every time) - even after a night in the hotel parking lot at 30F during the winter. Unfortunately, I don't have the luxury of jump starting from the truck that was used to tow the trailer if the Boxster battery doesn't have enough juice.

But your point is a good one and I'll take another look at them...

Street battery and a track battery.

I know storage space is probably a premium when you travel but it's an option.

Mike

The holder for the Odyssey PC925 is different than the smaller deka ETX14. So He have to have both and replace the tray as well.

Tom, with a full electrical system car I'm OK for about 6 week in cold weather then I have to run the car or charge it. I also run the PC925.
Jesse

Useful information about maintaining Odyssey batteries.

Dry Cell Batteries - Jay Leno's Garage

I learned: don't use a BatteryTender, it's not designed for AGM batteries, and will shorten their lives. Use an Odyssey or CTek charger.

Where does one get holders for batteries that will work in my Spec Boxster? Either Odyssey or Deka.

Look on Renline for the PC925. Also look at summit racing

Tom I have used one of these on in my boxster for a good 5 years. If you are able to keep it plugged in on a modern Ctek when not in use, you should get considerably more life and reliability out them. The Ctek will give you a mini battery reconditioning program while the car sits....then again I don't live in the desert!

Tom,

What suspension bushing kit are you going to put it when you get to it?

I'm not sure yet. Need to check the rules and see what my options might be. The suspension refresh will probably happen over Thanksgiving or Christmas so I have a little time get the parts together. I'll post up info when I have it.

Installed an Odyssey PC680 this morning!

Thanks to everyone for all of the advice about batteries. In the near term, I'll pull the battery disconnect after use and carry a portable jump station with me just to be sure.

PC680 (left) and PC925 (right) side by side. Quite a size and weight difference...
http://i1114.photobucket.com/albums/...pszws5bzvj.jpg

I found this mount for the PC680 online for $80. All of the parts are polished to a shiny chrome finish so I gave the top piece a couple of quick coats of black plastic-dip to minimize the bling factor (see pictures below)...
http://i1114.photobucket.com/albums/...psh6sxwkye.jpg

Removed the battery tray and attached the new mount by drilling appropriate holes and bolting from the bottom. The bolts that come with the mounting kit weren't long enough to reach thru both tray and mount. Problem easily solved with a quick run to the hardware store for a pair of longer bolts.
http://i1114.photobucket.com/albums/...psvmqoil9k.jpg

Mounted and ready for install...
http://i1114.photobucket.com/albums/...pseyldkrva.jpg

Here is the final install...
http://i1114.photobucket.com/albums/...psegcuz6o0.jpg

** Weight Update #6 **

Spec Boxster minimum weight with driver and fuel is 2,650 lbs. My goal is to be able to manage the weight of the car by adjusting the fuel load at the start of a race so I am near the min weight at the end of a race (with some margin for error).

At Laguna Seca, the total weight was 2,683 lbs with a 1/4 tank of gas. Subtracting 24 lbs for fuel (6 lbs/gallon x 4 gallons), says that the car/driver weighs 2,658 lbs.

With the battery change (-12 lbs) and a few other items (-5 lbs), the car should be down another 17lbs for a total car/driver weight of 2,641.

For now, I don't plan any more weight reduction until I get a weight check at the next race (POC AutoClub Speedway Sept 10-11).

The PCA rules say: no urethane suspension bushings, all bushings must remain stock.

I found that hold-down here for $80.

There's also the aluminum box style for $26.

Thanks for checking that info! I guess this makes the decision pretty easy.

If one were to install the optimum bushing set ....what would it be? I don't think I can go back to the spongy black bushings in the front end of the 986; nor do I desire race car solids. A urethane kit would be the ticket

Hi guys! Sorry to hijack the thread but who else than a knowledgeable group like you to help me with my little issue. I am the proud owner of a set of cloth GT3 seats for my Boxster (alien ones) and the Velcro on the seat base is worn and would not hold the cushion under the thigh in place. I see that the original Velcro strip is sown on so I am trying to figure out how can I replace it. Maybe some of you have had a similar issue and can help with some advice. Thanks! I can find sticky Velcro but that sticky part prob won't last long in cloth.