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'Smugglers-Box"...transfer the battery into it?

I believe placing this significant amount of weight within the wheel base would be a good mod as far as making a better handling car.


Has anyone seen a kit or done a DYI job of transferring the battery into the smugglers-box? Of course this is not an option to anyone who has A/C.

Thanks for any input(s).


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Old 10-03-2010, 09:07 PM
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I have A/C, but I am taking it out to make the car lighter. I was thinking the same thing. It would be an easy move and a good idea. If you feel like doing it yourself, a car audio place would have all the wiring needs to do the electrical and I'd suggest using a red top battery. they're smaller/lighter and sealed.
Old 10-04-2010, 04:33 AM
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Rennline Battery Relocation Kit - 925 - Porsche-Rennline, Inc.

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Old 10-04-2010, 04:50 AM
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I never really got this!

First why put it higher in the chassis where it is going to move the center of gravity and front roll center higher? This is why we lower a car.

Second, on a car with 50% more weight over the rear (and especially a 930) why would we want to move weight any more toward the rear of the car?

Seems a better place unless there is something in the way like a fuel cell, oil tank, spare or such would be as far forward, to the right, and low as possible.

I would look to the rear of the car first for weight reduction. Exhaust, euro bumper struts, rubber bumperets delete or euro's, rear seat backs, RS carpet kit, rear under carpet pads delete, fiber lid and or tail...
Old 10-04-2010, 07:34 AM
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Quote:
Originally Posted by 911st View Post
I never really got this!

First why put it higher in the chassis where it is going to move the center of gravity and front roll center higher? This is why we lower a car.

Second, on a car with 50% more weight over the rear (and especially a 930) why would we want to move weight any more toward the rear of the car?

Seems a better place unless there is something in the way like a fuel cell, oil tank, spare or such would be as far forward, to the right, and low as possible.

I would look to the rear of the car first for weight reduction. Exhaust, euro bumper struts, rubber bumperets delete or euro's, rear seat backs, RS carpet kit, rear under carpet pads delete, fiber lid and or tail...
Think about what Porsche does when they produce or make a mid-engine car...that large chunk of mass is inside the wheel base, unlike our 911 beasts which rest on top and behind the wheel base.

The closer you can take ALL mass from either end of the car, and move it inside the wheel base, the better it will ultimately handle. I remember filling my car up with heavy oak firewood from Canada(yes I know it's a bit crazy), and driving it down to So. California. In theory, it should have balanced the engines weight nicely...in reality it really made the car push/understeer at triple digit speeds(which when driving it was a bit scary)

I have "Shamu" to just under 2500lbs(1983SC converted to a 3.3L Turbo), so with a lot less surface area(in terms of aero drag/weight, fully gutted a/c(which includes all those lines running to front/back compressor, fan set-up in smugglers box, no rear seats, no rear panel with speakers, no radio, no electric antenna, and a whole LOT of other nooks and crannys where I got got crazy gutting superfluous stuff. That dead weight gone is free HP. This winter is Stage 3 of cutting out the fat...
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Old 10-04-2010, 07:54 AM
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Two snaps UP!

Excellent...thank you.

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Old 10-04-2010, 07:56 AM
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Yes the 914, Boxster, Cayman, & GT were touted as a more mass centered mid motor designs.

I get the centralized mass rationalization and it is a valid goal. But I suspect not over other design factors as noted.

For example, when it came to the heavy lifting (production racing) the 911 has been by far the go to car over such designs.

So, if someone is asking my opinion, such a mod is more in the car jewelry category and probably not perceivable on any measurable performance level by itself.

If the goal is to go faster, there are a lot of other things that have a better payback like driver instruction / time, tires, brakes, suspension...

Bottom line, it is all good and if one likes it just go for it and enjoy it!
Old 10-04-2010, 09:53 AM
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Quote:
Originally Posted by 911st View Post
I never really got this!

First why put it higher in the chassis where it is going to move the center of gravity and front roll center higher? This is why we lower a car.

Second, on a car with 50% more weight over the rear (and especially a 930) why would we want to move weight any more toward the rear of the car?

Seems a better place unless there is something in the way like a fuel cell, oil tank, spare or such would be as far forward, to the right, and low as possible.

I would look to the rear of the car first for weight reduction. Exhaust, euro bumper struts, rubber bumperets delete or euro's, rear seat backs, RS carpet kit, rear under carpet pads delete, fiber lid and or tail...
You can look into something called "polar weight", it's almost as important as "unsprung weight".... getting the weight inside the pole, i.e. within the perimeter of the 4 tires is a lot more important that bring the CG up a fraction. Moving the battery within the wheels is and a little bit higher is a better compromise.
Old 10-04-2010, 01:44 PM
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Come to think of it, it's an even bigger gain. 911's were designed to have RH drive, thus the put the battery on the LH side to "balance" out the driver. Seeing as we are talkling about US cars, bringing the battery inboard and to the right is even a better transfer of weight. Simple way to check is have someone with a set of scales weight the car both ways.
Old 10-04-2010, 01:49 PM
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Now you are cooking.

The battery is discretionary weight and using it to best balance the car as you note is what I am trying to convey.

Using my stock 85 as an example assuming I am adjusted to a 50/50 diagonal balance as most suggest my numbers with a driver in a mostly stock 85 911 were:

..............left / right =total
Front:......636 550 =1186
Rear:.......897 810 =1707
Total:.....1530 1360 =2893 lbs

The left hand side with driver weighs 1530 and the right weighs 1360 or 170 lbs less. This could effect threshold braking in the form of o premature wheel lock up.

If so, where from right to left should the battery go?


How about front to rear weighting?

My car was 1186lbs front and 1707 rear. This is 44% more weight to be supported by the rear tires than the fronts (a 930 is more like 50% more rear weight to the rear tires).

However, assuming a stock 930 with 205 and 245's that simplistically comes out to 20% more rear tire trying to hold the 44-50% more weight.

So where front to rear should the battery go?

Half way between the front and rear tires where it's pollar weight is minimized?

No. Probably best if it is as far from the rear wheels as possible.

Last, where is it best to have the weight on a car. As low as possible or higher in the car?

Thus, moving the battery as far to the right, as far front, and keeping it as low as possable would probably be more ideal if it is going to be moved.

Last edited by 911st; 10-04-2010 at 04:01 PM..
Old 10-04-2010, 03:54 PM
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you almost got it, but not quite.... Think of this... the further out from the center you have the weight, the more effort it is going to take to make that weight change direction quickly. So, in long sweeping corners (say the autobahn), once the car settles, it will be happy with the weight far out in front of center of gravity.... but if you are an auto-crosser or road course racer, you are going to want to get the weight as close to the center of the car as possible. If you have the battery weight a little behind the front wheels, but closer to the center, instead of way out in front of it, you will have a car that flicks from left to right better.

think of having a heavy weight on the end of a stick. Say a sledge hammer. Try swinging that hammer from the end of the handle, left to right quickly. Kind of a hard thing to do... Now grab that hammer mid handle and do the same. Much easier. Still the same weight, but closer the the center. Now try to think of having 2 of the same hammers taped together, weights out at the poles.... even though the stick is perfectly balanced 50/50 on each end, it's still going to take a lot of effort to get that stick to change direction... Now if you start moving the weights inward, the stick will be easier to swing back in forth. The closer you bring weight into the center, the better the car will handle. IMO, having the battery a couple inches higher, but over a foot inward and 3 feet to the right is a good compromise.

I know that you are getting all bent up about the rear engine of the 911, but there are a lot of other things that can balance out the nature of this beast out. i.e. spring rates, ride height, sway bar size and rate, wheel size etc....

Point of the argument is to get the most weight as possible as close to the true center as possible (in both height, front to rear and left to right) Then work on balancing the handling out with the other examples given.

Last edited by IMR-Merlin; 10-04-2010 at 04:36 PM..
Old 10-04-2010, 04:25 PM
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Hope what I am saying makes sense. I could look through some of my old boxes and get some reference books out. It's hard for me to put into words what I usually draw out when explaining things.
Old 10-04-2010, 04:56 PM
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If you think moving the battery from in front of to over the wheels is going to make any measurable difference in handling performance then it really should go between the seats.

Once it is a set as you say, the polar is probably not a big deal though it can help at autoX if you can make a big enough change.

You are not going to turn a 930 into a 914 or Boxster.

How about this, a 930 is like trying to drive a sledge hammer back wards. It needs a hand at the other end.

Go for it!

The best.
Old 10-04-2010, 05:34 PM
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Quote:
Originally Posted by 911st View Post
If you think moving the battery from in front of to over the wheels is going to make any measurable difference in handling performance then it really should go between the seats.

Once it is a set as you say, the polar is probably not a big deal though it can help at autoX if you can make a big enough change.

You are not going to turn a 930 into a 914 or Boxster.

How about this, a 930 is like trying to drive a sledge hammer back wards. It needs a hand at the other end.

Go for it!

The best.
Oh, by all means, the best place is in the passenger cabin, but then you best have a sealed battery and make sure you have one hell of a bracket to hold it in place in the case of a roll over... and what's the point of having a nice fast car if you can't bring someone else out with you to enjoy it....

But now that I think of it more, it may actually be better in the Smug box, after all you are trying to get weight onto that RF tire.... much better to have it behind it than in front of it.

Last edited by IMR-Merlin; 10-04-2010 at 05:43 PM..
Old 10-04-2010, 05:41 PM
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The bracket is reasonable and appears to be worthy of use, at under $200.

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Old 10-05-2010, 07:53 AM
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polar moment of inertia is best thought of like this:

Imagine you have a 2 blade propeller that weights nothing. If you put 10 lbs on the tip of each blade, it will be harder to bring up to speed (and slow down rpm) than if you put a 20 lb weight in the center.

The polar moment is the resistance of a car to yaw. Less is not neccicarily better. A low polar moment can be part of the reson why some mid engined cars "spin like a top" when they break away. Cars of the same weight with a more moderate moment are more easily "throttle steerable". In general a car should like to turn an a low polar moment is a means to that end but .
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Old 10-05-2010, 08:09 AM
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Mine is in the smuggler's box. Keith, it makes for a much better road course ride, believe me. Pictures at 6. My bracket was made from scrap metal I had lying around, and welded into the car.
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Old 10-05-2010, 09:43 AM
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Quote:
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polar moment of inertia is best thought of like this:

Imagine you have a 2 blade propeller that weights nothing. If you put 10 lbs on the tip of each blade, it will be harder to bring up to speed (and slow down rpm) than if you put a 20 lb weight in the center. .
LOL, that is what I was trying to explain in a LOT more words.
Old 10-05-2010, 11:26 AM
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Pictures at 6.
Can't really see the brackets unless I remove the battery. Simply angle steel clips welded in, with one of those aftermarket battery trays all 911's eventually need. Fits all Optima batteries.

Pat


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Old 10-05-2010, 03:11 PM
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Mine is in the smuggler's box. Keith, it makes for a much better road course ride, believe me. ...
Patrick,

Good to hear you could feel the effect. That is the most valid point of reference for doing the mod I have heard.

If it felt "much better" this might also be an argument that the front is sensitive to weight and where is it placed. If so all I am saying is put it the best place available. If one is carrying a spare tire and dose not have A/C the battery box with a lighter battery is fine.

I am not saying it is not an improvement. I am saying I do not think the polar moment is a very valid rationalization for the mod and that further forward, to the right and lower in the chassis would be even better.

And! That on the list of things that can be done to make a car (or driver) faster, this would be pretty low on my list after things like great tires, a book on driving, a strut brace, tire temp probe, or even deferred maintenance.

As for improvement, I suspect the real gains are from reducing the weight of the car about 20-30 lbs with a lighter battery and improving the the front wheel side to side wheel imbalance about 20%.


Using the propeller (lets say wheel) example is a simple and good way to explain what polar momentum is. However it dose not match the magnitude of what we are considering.

What we are doing is more like like taking a 20" 20lb wheel and moving a gram or two inward about 1/2". Not measurably going to effect the wheel via polar momentum.

However, move a little weight around on the wheel to get it better balanced and you have made an important improvement. Or lighten the wheel and we will be able to accelerate it faster.


Last edited by 911st; 10-05-2010 at 05:20 PM..
Old 10-05-2010, 05:14 PM
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