Final word on battery relocation...?

NoLift911 · 10-10-2004, 11:16 AM

First off I have searched and read many of the threads on this. Never seemed to get a definitive answer on this in terms of better or not for relocation of the weight.

This would be relocating a battery on an 84 Carrera to the smugglers box. I have A/C but I am removing that as well. My battery just bit the dust after 7 years. I have heard good things about the Optima but still not sure which would fit in the box. I have a monster of a battery in there now. I would probably go with the WEVO kit or the Rennline kit.

I also like the idea of a kill switch - this is not a dedicated track car but it is certainly moving in that direction. Mainly for DE events to this point but I am sure it will make it's way to a track car eventually. My hesitation is just that it is basically a garage queen with 30k miles on it and very pristine.

So I am removing some basic things that I rarely use A/C, stereo for some weight savings. These should be substantial as the stereo has a heavy amp and the Rod Birch sub enclosure with 8 inch kickers - this alone is about 30+ lbs. RUF bumpers are next, RS door panels and then a Protomotive turbo kit for a bit more go. I think it should be pretty peppy after this.

So back to the original question - to relocate the battery or not?

-Jeff
nolift911@hotmail.com

buster73 · buster73's Garage

Unless you are serious about track results you won't see a big benefit in daily driving or for DE events. Installing a smaller battery closer to the CG will of course reduce overall weigth, move the balance further back and reduce inertia. Without any other modfications this will not necessarily make you faster as it migth increase understeering in slow corners and make the car more nervous at the limit (though this can be fun on the track).

I just installed two Odyssey batteries in my 73 (original location) after my old batteries died. For track events I can take out one of them, but I don't really expect to see a significant difference. The car is still much faster than the driver.

widebody911 · widebody911's Garage

This is on my list of things to do this winter.

I don't think you're going to see an "oh-my-god-what-a-difference" change, but the combo of a smaller battery and centralizing the weight will make a small contribution. By the same token, this once change isn't going suddenly turn your car into a understeering pig ala M3.

NoLift911 · 10-10-2004, 04:06 PM

Yeah I am not expecting anything dramatic but it all helps and like I said I have a 60lb battery that reads 4.3 volts on my meter.

So if I am going the lighweight battery route I might as well do the full dealio IMO.

-Jeff

Zeke · 10-10-2004, 04:43 PM

Mine is in the smugler's box ala a very similar bracket the Elephant sells and can be purchased thru Pelican. But, the only reason I did that is beacuse I didn't have a decent way to attach a new battery to the boxes and the front pan was too rusty to support a battery. Doing it again, now with a new pan, might lead me to locate the battery at the front for ease of access and proper weight distribution.

Might not make a whole lot of differnce, but the smuggler's is higher. Low is good. If you have to carry a weight, put it as low as possible and if you can help with weight distribution at the same time, do that too.

Formerly Steve Wilkinson · 10-10-2004, 05:35 PM

I did the Rennline-kit relocation with a Bosch kill switch. the basic reason for the kill switch, in my case, was that I'd heard from some knowledgeable people that Optima batteries don't like to sit un-used for long periods of time--couple of weeks, a month. Other posters have said this is ridiculous, they leave their Optima in all winter and it starts the next spring no problem. I dunno. But in any case, I shut the battery off any time I'm not going to be running the car for a week or more, and it's just another cute Porsche-ness, as far as I'm concerned... "Yessir, this is a real complicated car, I've gotta crawl into the trunk and put this key into this socket to energize the electrics...stand back or it might fry your eyes..."

Hey, I'm happy.

Stephan

NoLift911 · 10-10-2004, 06:39 PM

Stephan,

I would like some details on the install you did - I think I will go with the Rennline kit as it has a nice cover and looks cool. What battery did you go with and where did you get your kill switch? What about your cables and wiring did you have to fab up new cables?

I am confused about the kill switch for saving the battery? What exactly are you killing? How does this shut off the battery?

Thanks,

-Jeff

Formerly Steve Wilkinson · 10-10-2004, 08:09 PM

Well, the details will be pretty obvious once you get the Rennline kit. There are a bunch of holes in the aluminum cover to which you can bolt the kill switch from below, which is a standard Bosch item that Pelican carries. When you turn it off, it totally disconnects the battery (via the ground cable) from the car. It has the same effect, essentially, as removing the battery from the car and putting it on the garage floor.

I don't know why--or whether--that makes a big difference, but one Porsche guru (Steve Weiner) who I will follow anywhere told me that it's what you need to do if you run an Optima battery and want it to last.

If he's wrong, that's fine, I'm happy to line up right alongside him in the "wrong" line.

Stephan

Randy Webb · 10-10-2004, 08:18 PM

What exactly are you killing?....

- You are killing all current draws on the battery from the car (such as the clock or an alarm system). The battery will still discharge ("self-discharge) but at a much slower rate. Note - this happens even tho it is not connected because an emf is setup between the + terminal and the - terminal. There are no doubt chemical changes as well in storage. It is best to just use a maintainer.

Elombard · 10-11-2004, 04:46 AM

SO in terms of weight distribution what did we decide. No Big deal either way? All things equal leave it in the front?

Seems like if Steve Weiner and Chuck like it I will get in the wrong line with them as well!!

304065 · 10-11-2004, 04:54 AM

In terms of weight distribution, relocating to the smugglers box does make a difference.

However, that difference is not meaningful for street driving, and may actually make things worse, e.g., for the street you probably WANT a little higher polar moment of inertia. Also, going from a 60 lb battery at CG + 36" that's 12" to the left of the centerline (I don't know the actual station) to a 30 pound battery at CG +15 WILL have an effect on corner balance, which would have to be reset.

Hey, if it blows your hair back and looks cool, I say go for it, but from a performance standpoint it's about #100 on my list of must-do's.

Bill Verburg · Bill Verburg's Garage

There is fair reduction in the polar moment of the car, if not the actual total weight. The reduction in polar moment will contribute to better response to yaw and pitch, the car will rotate more quickly and repond to pavement irregularty more quickly.

NoLift911 · 10-11-2004, 05:48 AM

What type of battery are we talking about for the smugglers box? Do I need additional cable for the rewire?

-Jeff

Zeke · 10-11-2004, 06:24 AM

Quote:

Originally posted by Bill Verburg
There is fair reduction in the polar moment of the car, if not the actual total weight. The reduction in polar moment will contribute to better response to yaw and pitch, the car will rotate more quickly and repond to pavement irregularty more quickly.

I don't doubt your wisdom, but if we're gonna split hairs, I'll cite something from my chasis setup and handling book. The 911 has a higher polar moment that can't be changed much due the rear engine configuration. The 914 has a low PM. The 914 doesn't give too much notice before spinning and spins like a top. Of course, the 911 is somewhat the opposite. By keeping some weight low and to the front, it helps balance the effect.

Sure, the front steering might feel a tad more responsive, but the back end can't reciprocate. This might very well be the basis of the car's inherent tendency to understeer. Why exacerbate the problem? Now, if my car had front bumper weights, I would remove them in the interest of overall weight reduction. If I can move necessary weight around, I will do it to the maximun overall benefit.

Note: I use an Odessy style 20 something lb. battery and it's located in the bottom of the smiuggler's (maybe 2 " below the Rennline position). It uses a shorter battery cable than if mounted in front. So, there are pros and cons to each position.

Just a couple cents worth of theory............. Of course the subject is a lot more complicated than I present.

Tyson Schmidt · 10-11-2004, 07:04 AM

Polar moment aside, I like the fact that it moves the battery from the driver's side to the passenger's side.

Bill Verburg · Bill Verburg's Garage

Quote:

but if we're gonna split hairs

Not splitting hairs at all, the battery relocation will be on the same order of magnitude as f/g bumpers. I haven't relocated my battery but there was a very noticable improvement in both pitch and yaw response when I did the bumpers.

The back end doesn't need to recipricate it more or less follows the fronts lead. The front needs to start any rotation of the chassis in either the xy or xz plane(assuming the car is going forward on its wheels).

You are right that weight reduction to the rear will be less noticable/effective than weight reduction at the front and that weight reduction high is better than weight reduction low. This latter is one of the reasons lt wt tails are noticably nicer than stock ones and why race cars don't have sunroofs.

One of the biggest differences between the long hood and short is the weight of the bumpers, this makes a very noticable impact on the so called nimbleness of the chassis is question, another term for low polar moment.

On the earliest 911s the factory used iron weights located in the extreme front corners of the front bumpers to increase the polar moment of the cars, it was felt by the factory engineers that the increased polar moment would make the car more catchable by nonprofessional drivers. This of course worked but was later dropped when other methods w/ fewer undesirable side effects were found

These other methods included alignment specs, shocks, wheel/tires and wheelbase increases.

911SCfanatic · 911SCfanatic's Garage

Quote:

Polar moment aside, I like the fact that it moves the battery from the driver's side to the passenger's side.

That is a good point. Wouldn't be a bad idea to start counteracting my weight.

NoLift911 · 10-11-2004, 11:24 AM

Thanks for all of the replies - I think I will go the WEVO kit route since it is FG instead of aluminum with a minimal weight savings there. I think I am going with the Westco Miata battery as it is lightweight and seems to have enough CCA for my application.

Prolly add a kill switch too for good measure "while I am in there"...

Thanks for the replies.

-Jeff

MuffinMan · 10-11-2004, 11:46 AM

I posted my installation of the Rennline kit a few months ago. I used an Odyssey battery (~15.4lbs) instead of the heavier Optima battery they suggest in their kit.

MuffinMan · 10-11-2004, 11:52 AM

Quote:

Originally posted by nolift911
Thanks for all of the replies - I think I will go the WEVO kit route since it is FG instead of aluminum with a minimal weight savings there.

The weight of the aluminum materials in the Rennline kit is almost nothing. It weighs maybe a pound or two, so take that into account when making your decision. Both kits have their pros & cons, and I bought mine at the Hershey swap since I loved the way it looked in the demo car. I have never seen a WEVO kit in-person, so I cannot accurately compare & contrast.

The Odyssey battery is powerful enough to start the 3.6 with high-torque starter, but it definitely isn't as strong as the Optima it replaced.