UPR Trunk Mounted Battery Box
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In the eternal search for better ET's at the track and more modifications to perform to our '99 GT project car, we seem to have gone hardcore. Everyone knows that removing weight from your Mustang will increase acceleration and therefore decrease track times. God knows we've ditched every possible pound from the car that we didn't feel was needed. But did you know that weight transfer and the location of the weight in your Mustang is also very important? Since we mainly use our GT in drag racing events or for daily driving, we were looking for ways to improve traction under hard acceleration. One such way is to move weight from the nose of your car to the trunk so that when the car launches from the line, the front of the car can rise more, to shift the weight over the rear axle where it's needed most for grip.
This is where our UPR trunk mounted Battery Box comes into the picture. UPR Products sells a nicely manufactured stainless steel battery box kit that allows you to safely mount your battery in the trunk. Our factory battery weighed a massive 37 pounds which is now over the right rear tire. The kit has everything to complete the install
including power wire, ground wire, box with lid, rods to mount to the trunk and all other necessary hardware. It is designed for both stock batteries as well as aftermarket batteries.
The box itself weighs about 8 lbs but this will serve as more downforce over that right rear wheel so we're not concerned about adding this small amount of weight to the trunk. Getting the battery off the nose was the important piece.
To go directly to the order page for this item on UPR's website click HERE.
Moving a battery to the trunk of your car is not a plug-n-play option, so expect to do a little grunt work in the installation. Anyone with basic knowledge of turning wrenches or tinkering with your car will be able to tackle this. Having an assistant for some of the steps is very helpful but not required. Our install took a bit longer because we were taking photos and weighing all the parts as we went. We also had to re-think the placement of our nitrous bottle since both items could not fit over that right rear wheel.
Strip the car
First of all, we removed that massive stock battery and the tray that holds it in place from the engine bay. Wow, was it dirty under there! We then removed our rear seat delete kit to better access the wiring we'd need to run to the front of the car.
In the trunk, we removed the trunk mat and nitrous bottle brackets. We then set the box in the car where it needed to be positioned and marked the 2 holes with a pen to drill them out. Remove the box from the car temporarily and then pull out the rear trunk panel to have better access to mount your negative cable. These are just held in place with plastic clips.
Mounting the box
There are 2 threaded rods included with the kit that go down thru the box and thru the trunk floor. You will need to get 2 nuts on the underside of the trunk to hold the rod in place. This requires that you drop the gas tank down to reach that area. Even though this sounds like a huge chore, it wasn't as bad as expected. There are 2 straps that hold the gas tank in place, so you only need to remove the 2 14mm bolts holding these straps in place. (We questioned Ford's design here to have only TWO bolts holding on a gas tank.) We recommend having the gas tank as empty as possible for ease in this install. We only needed to let the tank hang down (not remove totally) to reach the ends of the rods to get a nut started. We let the tank rest on some wooden blocks to relieve the pressure from pulling the fuel lines off. Drill your two holes slightly larger than the rod diameter.
From the inside of the trunk, place 2 more nuts (14mm nuts provided) down on the rods to hold the bottom of the box in place. This will tighten up the rods against the lower nuts you just installed under the car. Once that is in place, you can set the battery in the box and mount the bracket over the top with 2 more nuts provided. Our battery was too big to fit in the bracket's edges so we turned it upside down and bolted it on. This was not a problem since the battery was big enough to be up against the mounting rods for stability. The bracket edges appear to be made for an aftermarket battery that would not be stable in the box without the extra hold-down. UPR mentioned they were working on an adjustable bracket for this in the future.
Next, we ran the negative cable thru the box and tried to locate a solid grounding point for the battery cable end. We used an existing bolt on the back panel and scraped off paint around the base for a good connection. (See photo below.)
When installing the positive cable through the battery box, be EXTREMELY CAREFUL not to touch the positive battery post on the battery. Run the positive cable through your interior towards the front of the car. We went down under the rear seat and up the driver's side just under the carpet. When you get to the kick panel at the foot rest, remove that plastic panel. There is a rubber plug you can push out up in that hole that allows you to push the wiring through. This will run the cable in the inner fender well which leads to where the old battery was. Fish it thru the holes and pull through under the hood.
Finishing under hood
We thoroughly cleaned where the old battery box was. Mother nature had left us plenty of leaves and debris to wash out. There was some minor rust under there that we plan to touch up later. Once we were satisfied it was in show worthy condition, we began hooking up the cables. The old negative cable can be mounted using the old screws holding the battery tray in place. The positive cable from the trunk must be connected to the old red cable under the hood. This took a bit of creativity since there was no specific hardware in the kit to accomplish this. Once we were sure the connection was super tight and sturdy, we put the plastic positive post protector over the end and taped up with several layers of electrical tape.
Finishing up the trunk
After putting all of the interior pieces back together, we headed to the trunk again. We connected both terminals to the battery, making sure not to touch anything metal with the wrench. The wrench slipped at one point and touched the edge of the battery box which sent a shower of sparks flying and left us with a melted wrench handle and small arc in the box edge. So it might be best to put a piece of cloth over the box edge while doing this.
We re-attached the gas tank with the 2 bolts and then reinstalled the rear trunk panel. We had to cut the panel slightly to allow the negative power cable to slide through but it was not noticeable after the install. After attaching the lid of the box with the 2 remaining nuts, we cut the excess from the threaded rods so they didn't protrude so far up. You can leave them if you wish. We also had to cut the trunk mat to fit around the new box since you can't really leave it under the box or you'd never be able to lift it.
Since we also had to work a Nitrous setup into the equation, we were forced to build a custom design in the trunk. We mounted the nitrous bottle in the spare tire well on a specially built board. We've come to realize that the spare tire was just a nice safety convenience and 30lbs of dead weight to us.
We were very satisfied with the battery box kit after it was all said and done! We moved 37 pounds from the nose of the car to the rear to balance out the weight distribution. We can also jumpstart the Mustang from the trunk now if needed. For under $150, this mod will be well worth the effort at the track. We imagine this would also help the car from pushing into corners on a road course but haven't had the chance to try that yet. Weight distribution is a major factor in any type of racing environment. Combined with this, removing the front sway bar and throwing on some slicks, this could just about pull the front wheels off the ground heading down the 1320!
Written by: Steve Shrader, YMR