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GTO TEX's 1966 GTO

2020 February
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Last Indian

Grand Prix battery relocation

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Last Indian

I will preface this with why I did this to begin with. The average battery weighs around 50 pounds. In nearly all cases the battery sits ahead of the front suspension, as well as above the center of gravity, which gives the weight of the battery a positive percentage advantage of weight over the suspension. This varies from car to car, but in all cases it’s a disadvantage for handling and braking, in FWD cars it is really very detrimental.

So, first of all this requires, at least if you do it the way I will explain, a couple days down time. If you want to make this easy for working. This requires the removal of both front seats and the rear seat, as well as the carpet and the back trunk barrier. Additionally the trunk carpet, the back covering were the tail lights are, the spare tire, jack and so on. You’ll need about 30 feet of 1/0 welding cable, lug ends, a 300 amp fuse block with fuse that will get mounted in the trunk, for safety. Some good aluminum tape to hold the cable in place under the carpet and also too act as noise shielding for the cable. You will need to fabricate a mounting arrangement for the battery in the trunk as well as an arrangement up front to connect the the hot cable to the system that can be isolated and safe! I will show all of how I did this, but you can obviously do what you feel works for you. In the end remember this, there will be a voltage drop over that distance due to resistance, it’s just physics! So the 1/0 cable helps that, bigger cables, such as 2/0, 2/0 and 4/0 will carry higher voltages and amps, but also more weight and less flex. Plus this is 12 volts not 110 or 220 and the highest amp requirements are very short duration. 1/0 carries more than enough power to start the car and fry the entire system without much impact to the cables! An 1/0 cable for ground in multiple places helps minimize the voltage drop as well, so I will show where and how I make all of these connections.

 

You can use whatever battery you choose, but if you wish to keep your spare tire, this applies to 1997-2009 GP’s only, as I don’t know the configuration of other car trunk area, the only one that will allow that is the Odyssey battery, model pc925 series. They make it in both left and right hand + terminals, this is not a wet cell battery! 

 

When I did this conversion I never planned on doing a how to so I don’t have detailed photos of everything I did. So in those instances I will just have to explain what I did as best I can.

 

Starting at the trunk, in the spare tire well there is a bracket that houses the threaded rod to hold the spare in place. Remove that rod. Drill three holes for #10 sheet metal screws. Using three pieces of nylon you will now make the base plate for the battery. The bottom piece will be two pieces 3/8 thick. They will go on each side of the bracket and form the bottom base perimeter of the upper nylon piece that piece will be ¼” thick and three corresponding holes to match the three hole drilled in the bracket. The assembly of nylon pieces maybe glued together with a good adhesive. In this nylon assembly you will need to configure threaded rod with backing nuts positioned properly for a clamping bracket for the battery as well as taking the spare tire hold down rod marking on the nylon where it will come through and drilling a clearance hole through the nylon plate as I show in the finished assembly. Taking the styrofoam piece that the spare sits on and cut the bottom out to go over the new nylon plate assembly. Other areas of the styrofoam will need cut as well for clearance of the battery and cable exits.

I will write more as soon as I can.

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Stewy

Awesome, thank you @Last Indian! Looking forward to when you have availability to post more!

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Last Indian
On 1/16/2020 at 9:41 AM, Stewy said:

Awesome, thank you @Last Indian! Looking forward to when you have availability to post more!

Additionally, I forgot too mention that the Odyssey battery weighs about 26 pounds, sits behind the rear suspension and below CG. So this has a positive effect on handling and braking as well as weight distribution. The movement of the standard wet cell battery @ 52lbs from it’s front location to a 26lb battery to this rear location is the approximate equivalent of taking 200lbs out of the front end. This may not make sense to some, but if you just think of a teeter totter and how moving it on one of the three fulcrum points it has and changing the weight at each end effects it mechanical advantage, then maybe it will make some sense.

Both positive and negative 1/0 cables exit the styrofoam spare tire holder at the back end of the inside trunk, at centerline of the trunk and enter the double panel area, (rear of car). At this point the positive cable goes right, (passengers side), and goes to the 300 amp fuse block. The negative cable goes left and gets bolted/grounded at the back panel. So at this point both the positive and negative cables are somewhat short. 

Now you need two cables that will run from the trunk area to the front of the car. The positive cable will connect to the other side of the 300 amp fuse block. This cable now exists the double panel at the back of the trunk, runs under the passenger taillight and continues to run next to the inner fender/trunk floor and is held in place, at least intermittently, by the aluminum tape, it continues into the backseat area. Then running next to the inside rocker panel/floor area to the front firewall. Here you need to at least intermittently use the aluminum tape to keep the cable in place. In the process of running both cables keep in mind the need to avoid pinch points and sharpe edges. At this point you will need to, for ease of access, remove the passenger side tire. Once done look at the firewall, just inside and above the frame there is a square plastic body plug. You need to remove this plug. This exposes the inner floor board that slants upwards to attach at the firewall. Here you need to hole saw the appropriate size hole that will allow you to install a rubber grommet that when finished will fit the 1/0 cable somewhat close and this needs to be times two, one positive, one negative. Or one larger hole with a rubber grommet that will allow both cable to pass through. Now continue and run the cable through and into the engine compartment. You will also need to cut two holes in the plastic body plug so you can reinstall that plug, the holes in the plastic plug should be tight to keep any water out. When finished I filled this area with great stuff to ensure water tightness, then trimmed any excess foam, then installed the plastic plug.

The long run negative cable will connect at the battery just like the short negative cable does, but when this negative cable from the battery enters the double panel it goes to the passenger side. This cable will then run inside the double panel and exit at the same point the positive cable exists and will run next to the positive cable all the way to the front. It will need to be taped in position like the positive cable and exit through the grommet hole that you previously drilled. 

Now we’re in the engine compartment. I will post more soon.
 

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If you’re wondering about the rags around the battery? This is a current picture, and while I’m working on the car I disconnect the battery. So those rags help to keep the cables isolated from the terminals.

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Edited by Last Indian
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Stewy

Thank you again, @Last Indian! Appreciate the nicely-done write up; this has certainly helped me in my thought process on how I would like to do something similar. Thanks again!

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Last Indian
9 hours ago, Stewy said:

Thank you again, @Last Indian! Appreciate the nicely-done write up; this has certainly helped me in my thought process on how I would like to do something similar. Thanks again!

You are most welcome, hope it helps you!

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