Relocating battery to rear beneficial for pro touring cars

[PT Sportwagon]

I know that relocating battery to the passenger rear of the car is beneficial for drag racing, but what about cars that handle like a pro-touring car. just wondering if it would be beneficial to relocate my battery to the spare tire well. Which is in the pass rear.

Tim

[wolf28]

I imagine anything that helps get closer to a 50/50 weight distribution is going to be beneficial.

[Vegas69]

Exactly...

[neki67]

It was one of the first things Herb Adams adviced of doing. On a 2nd gen F-body it would shift the weight distribution with 1 percent. E.g. from 56/44 to 55/45.

[chicane67]

Looking at it from a fulcrum point of view... it takes roughly 300 pounds off of the front end.

[bbcc]

The current weight balance of the car will determine what positoin would be best for the battery. Idealy you would want to place it as close to the cars IC for best handeling. But if the car has less than desirable weight balance right now, the battery should be used as bias. Avoid placing weight at the far extremities of the car. If you decide to move it to the trunk, keep it at or ahead of the axle center line.

[parsonsj]

keep it at or ahead of the axle center line.Bingo! Whenever you have weight you can move around, try and keep it between the axle centerlines, and as low in the chassis as possible. In the case of the battery, the very best location would be under the rear seat.

jp

[novanutcase]

Question:

Would it be best to center it over the rear axle or on the passenger side in front of the axle under the rear seat?

John

[Vegas69]

We are talking about inches here. Anywhere is better than the factory position on a rear wheel drive car especially in the muscle car era.

[parsonsj]

John,

If you have the choice, center weight is better weight. I'd put it under the rear seat area on the passenger side, as close to the middle of car as you can.

Since you have the choice. :)

Todd's got a great point: given our 40 year old front-heavy cars, anywhere behind the driver is better than the factory location.

jp

[John Wright]

Looking at it from a fulcrum point of view... it takes roughly 300 pounds off of the front end.That is interesting....never thought of it in that way before. So like the others were saying, staying as close to the Centerline as possible keeps that fulcrum as short as possible, so you don't have a 30lb battery effectively weighing 300lbs due to it's position within the car.

[Damn True]

Bingo! Whenever you have weight you can move around, try and keep it between the axle centerlines, and as low in the chassis as possible. In the case of the battery, the very best location would be under the rear seat.

jp

Assuming my '68 Camaro, if I were to move it to the pax compartment in the back seat area vice the trunk, I'd assume it would be even MORE important to have it in a sealed and vented (externally of course) battery box?

That area is going to get busy on my car. I plan to put a fire system and accusump there as well.

[novanutcase]

John,

If you have the choice, center weight is better weight. I'd put it under the rear seat area on the passenger side, as close to the middle of car as you can.

Since you have the choice. :)

Todd's got a great point: given our 40 year old front-heavy cars, anywhere behind the driver is better than the factory location.

jp

Theoretically though, wouldn't it be better to offset the driver weight with the battery right down the middle of the rear passenger side of the seat? Wouldn't this give you the opportunity to take advantage of the polar moment of inertia?

Granted, your talking about my fat ass versus a 30 lb battery but any offset would help right?

Also, would the added weight of the extra cabling to the engine compartment add to the power to weight ratio?

John

[parsonsj]

True: Sure. No need to breathe battery fumes, though gel-type batteries don't emit fumes (e.g., Optima). In case of a crash, I guess you'd want the battery to be as protected from getting close to you as possible.

jp

[parsonsj]

John,

You're right, it is about MOI, but weight splits left to right have a much smaller effect than weight splits back and front. It's because most vehicles already have centered mass left vs. right due to engine and transmission placement.

Front to back has more effect since the length is much larger than width of our cars, plus vehicle tires are on the outside edge left vs right, but not front and back.

So put that battery slightly on the passenger side, and get yourself on a good diet, and make your car all it can be! :)

jp

[BAD68GTO]

Please do not put the battery in the passenger compartment for safety reasons. I put my battery in the trunk in a sealed battery container with a small vent tube to outside of the car. I also had to run an additional ground ire to my engine and tie the heads together with another ground with my ignition system as the increased distance caused my ignition to not ground enough and you get shocked setting the timing-lol. Ran the extra ground wires and all is well.

[GetMore]

It seems to me like there's no right answer for the perfect location. If you want high speed stability you want to place the battery farther back. If you want quick steering response then you want the battery closer to the center.
In both cases lower is better.

Regarding the battery being in the passenger compartment: While it would be a good idea to have it sealed off, solidly secured, and externally vented, and an even better idea to have it outside the pass. compartment, lots of OEM applications have the battery in the passenger compartment, and they don't even bother sealing it.

BMW and Volvo place them in the back, near the bumper. If it's a wagon or SUV then it's in the passenger compartment.
GM places batteries under the rear seat.

[Vegas69]

I like mine in the trunk so it's easy to access for the battery tender and disconnecting while working on various systems. That will also be a good place for it if you decide to run a manual cut off switch due to a sanctioning body.

[69stang]

I was pondering this a month or so ago and decided to move it from the trunk to behind the pass seat, mostly for the reason to get it between the axles but also to the rear. Also, with the major changes, it is where it fits best. I did think about a fulcrum penalty so-to-speak as chicane67 pointed out but didn't have any idea on what it might be, didn't bother to do the math.

[novanutcase]

I was pondering this a month or so ago and decided to move it from the trunk to behind the pass seat, mostly for the reason to get it between the axles but also to the rear. Also, with the major changes, it is where it fits best. I did think about a fulcrum penalty so-to-speak as chicane67 pointed out but didn't have any idea on what it might be, didn't bother to do the math.

Was there a noticeable seat of your pants difference when you relocated the battery between the axles?

John

[69stang]

Was there a noticeable seat of your pants difference when you relocated the battery between the axles?

John
Its not running yet. In fact, the battery isn't sitting there yet as I've been completely framing the car and haven't finished with the bracketry and the enclosure. I'll eventually post pics of the build.

[John Wright]

Short story:

I had a S10 w/355, mounted the battery in the bed near the tailgate on pass side. learned a good lesson about mounting batteries. One morning on the way to work, I approached an intersection with a stop light, a van pulls out and I T-bone him in the middle of the intersection. The battery flew out of the truck and landed about 50 yards down the road with the cables still attached. Luckily that Group 24 battery didn't go through the back glass and hit me in the back of the head....or hurt some innocent bystander in another car.