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View Full Version : Relocating battery to the trunk


KaKa
04-13-2004, 06:22 PM
I used to run a small battery, but after installing an alarm and stereo system it was drained and recharging made it unreliable. So I opted for a larger battery, unfortunately it weighed twice as much as the previous one. I felt the noticeable weight change and it didn't launch as quick. I decided to move it the rear.

If I had to do it over again I would recommend
-a sealed battery, optima red $100 at costco
-marine battery box that can be had at any walmart,
-2 threaded rods, 6 nuts, 4 washers, 2 lugs, 1 connector, electric tape and shrink wrap from home depot or mcmaster-carr
-3 rubber grommets at an autoshop
-25 feet of high flex welding/battery cable from http://www.mcmaster.com/.
-a fuse

I went with Moroso blue battery box, since I need to vent the fumes from my open battery. The plastic grommets where flimsy, so I bought new ones to fit 1/0 gauge battery cable. 1 or 2 gauge cables would work as well, but note that resistance increases with length, but decreases with increasing diameter. The blue box was not worth ~$100, as stated before get a sealed battery and a marine battery box instead.

First thing is to look over the stock battery connections. The ground is attached to the chassis beneath the battery and then to a bolt on the manifold. The positive end has two ~8 gauge cables and one fat 2 gauge. The smaller wires run into the fuse box to provide power to the accessories and charge from the alternator. The fat 2 gauge wire goes to the starter. Connect the smaller wires to the 2 gauge wire with a cable connector. I then connected my 1/0 gauge cable directly to the starter.

Second I found a hole in the firewall to run my cable into the cabin. It's located in the passenger side wheel well, see pictures. I drilled a larger hole to accommodate the grommet and fed the cable through to the other side. You'll have to move the ecu out of the way, push some of the carpeting aside, as well remove the rear interior panels. I then ran cable to the rear.

I chose to mount the battery box in the trunk on the passenger behind as close to the rear axle as possible. The gas tank is actually located beneath the rear seats, so it's safe to drill in the trunk. Drill two holes into your box and through the trunk for the threaded rods that hold down the battery. Use the nuts and washers to keep the rods in place. I used the excess cable for the negative connection. There are several seat belt bolts you can as your ground. One thing I have yet to do is attach an appropriate fuse for the positive cable, as a recommended safety measure. Any recommendations would be great.

The car starts the same and the weight is off the front end.

twitchy
04-13-2004, 06:32 PM
thats a nice writeup....

but can you honestly say you felt a difference in your launch for the sake of 20 pounds, which stayed in your car but just moved??

nismo2491
04-13-2004, 06:44 PM
every bit helps man, trust me. the problem is that even if it is a sealed battery, if your drag inspector at the track is a dick he won't care and will make you get a sealed box.
KEvin

morpheus8486
04-13-2004, 07:04 PM
How much is this costing you total? Nice write up btw. Be sure to post some pics of the finished product.

old_s13
04-13-2004, 07:09 PM
oem starter wire is 4ga...

wiring used is a bit excessive in size but it works...

check marine supply stores for breakers, you'll need a 150A breaker minimum (depending on how much current your electrical system draws).

Mr. Foully
04-13-2004, 08:56 PM
Dude, for an FNG, you're damn helpfull!

S13SilviaGirl
04-14-2004, 09:39 AM
anyone planning on going to DD's or AUtoX's make sure that shit dosnt move or they won't pass you on the tech side....FYI.

KaKa
04-14-2004, 11:11 AM
oem starter wire is 4ga...

wiring used is a bit excessive in size but it works...

check marine supply stores for breakers, you'll need a 150A breaker minimum (depending on how much current your electrical system draws).

- yeah i kinda went overboard, it might have been better to use 2 or 1 gauge

thanks for breaker info

- maybe my ass is too sensitive, but as far as weight distribution it is noticeable

- it doesn't budge at all, and there are rules at some track events like a sealed battery box in hatches, but not in coupes, and I think an external kill switch at the drag strips, but this is at the top of my head so check rules and regulations before doing your setup

- the cable and battery would be the most expensive, about ~$40-55 for the cable and $100 for the sealed battery, everything else would run $20-$30. the homedepot cables are not very flexible and may bulge out under your carpeting or panels.

KaKa
04-14-2004, 11:17 AM
Dude, for an FNG, you're damn helpfull!

You'd be suprised how long I've been here and there on this forum. I still remember the CA and SR battles. This is my wife's car, bought it new in 95. I'm usually hanging out at the rx7 club forum.