Battery Relocation

[Locobob]

So I am finally making some progress on my car and am working on relocating the battery to get some weight off the nose. I'm currently in a bit of a quandary over where to move and how best to mount the battery. The battery itself is a 25lb Odyssey gel cell type. I have identified two locations I think will work. My first thought was to put the battery in the storage compartment behind the passenger seat as many others have done. But I want to be able to track the car occasionally and so I am trying to make this install comply with the NHRA rule book - not an easy task I am finding.

Storage compartment behind the passenger seat.

Advantages:
Weight low in car, very close to right rear tire for traction/polar moment of inertia advantages.
Fits nicely in existing structural fiberglass compartment.

Disadvantages:
NHRA regs dictate attachment to frame - nearest and only viable frame is nearly a foot forward of where the battery will sit, the solution I have been working on is kind of a shelf type aluminum bracket (see pics) which would sandwich this frame section (with bolts going through it) and extend rearward under the compartment holding the battery. While the fiberglass bucket will normally take the battery's weight I have serious doubts that my aluminum bracket would hold on its own.
Since the compartment is part of the cars interior I would also have to fabricate a plate over the top of the battery to seal it off from the cabin - NHRA requirement.
Lost interior storage space.




Here are some pics of what I'm talking about:

Battery sitting in rear storage bin


Underside of rear storage bin - frame area for mounting support bracket visible


Support bracket in place


Battery in position on support bracket - lot of weight way out from the only mounting point creating a serious lever

[Locobob]

Secondly I have been considering mounting the battery behind the differential on the rear frame cross-member. If I were to go this route I would encase the entire battery in an aluminum or plastic box to protect it from dirt and road debris. Note in the pics you can see that the rear cross-member has been bent, probably by jacking I would guess - I should look into getting this fixed up at some point.

The advantages here are:
Weight just behind the pass. rear tire for better traction and F-R weight distribution.
Cross-member allows easily accessed and exceptionally sturdy NHRA approved mounting point.
Well protected from road as it is behind and above the differential and exhaust.
Outside of drivers compartment - negates NHRA cabin rules.
Easy to access wiring from under car.

Disadvantages:
Have to jack car to access battery - probably not a really big deal as I'd have a positive terminal post under hood to jump if necessary.
Weight behind the rear axle - good for drags but less so track use that requires turning.
Relatively close proximity to fuel tank? Not sure if this location would be great in a collision.
Probably wouldn't work with factory spare tire assembly - but I don't have a spare anyhow so not really an issue.


I have purchased an NHRA approved push/pull style kill switch. Either way I mount the battery I think the kill switch will be best mounted to the rear cross-member and the rod will run towards the rear fascia not far from the tail pipes. For street use the rod will sit slightly inboard of the rear fascia so it is out of sight and less likely to be tampered with. For track use I will add a 6in extension to the rod so that it protrudes past the bottom of the rear bumper.

Mocked up showing possible location on rear cross-member




With kill switch




So what do you guys think?

[scottfab]

Bob,
Why not mount it sideways on the beam? thus exposing the connector more easily. A plate could cover the terminals. The sealed batteries can be mounted any direction.
I like the idea of shifting weight not only rearward but low.

[Locobob]

It could go sideways on the beam, but it wouldn't make a huge difference... the battery is about 6in tall and about 7in on all sides and would still basically have to mount flush with the bottom of the beam. Would make terminal access a bit easier I suppose.

[Locobob]

I'm thinking maybe Scott has the right idea here. With the battery on it's side the positive terminal is right there next to the kill switch that in must connect to (NHRA requires kill on pos. side), the negative could go right to the cross-over beam. I could run a flat bar down the back side of the battery which would be bolted up to the front side of the cross-member and an L bracket connecting to the beam on the back side then dropping down - both would tie into a plate to hold the battery at the bottom. I think this may be the simplest, most effective solution.

[scottfab]

You could make the brackets (slotted) adjustable for various battery
size variations. Does the spare wheel cover hide the battery?

[Locobob]

Well the box will hang with the battery on its side and the terminals will be near the top, backside of the box is closed and will face forward on the car so I doubt much water will get into the box. So... not sure if a drain hole will be necessary.

[scottfab]

Oh that's right, on it's side.
Never mind

[Locobob]

Here it is all put together