Trunk Mounted Battery

dakota · #1 (**permalink**) 08-23-2001, 08:35 AM

I went back and looked at the old posts about mounting the battery in the trunk, but still have a question. It was pointed out that no matter what, the engine needs to be grounded. Should I run the battery ground all the way up to the engine, or would a ground from the battery to the frame in the rear and a ground from the engine to the frame in the front suffice??

Also, does anybody have the physical dimensions of the battery that fits in Classic's battery tray?? I forgot to measure it last night, and want to pick up a battery today.

Thanks,
Wade

jwinkler · #2 (**permalink**) 08-23-2001, 02:24 PM

When we moved my battery to the trunk, we grounded the negative post to the frame right below the battery, and then grounded the block to the frame up front (actually just made sure the existing ground strap remained).

As for battery size, I can tell you for sure when I get home, but the battery box that fits in the cubby behind the rear wheel well is one that I picked up off the shelf at autozone. The one that came with the Summit relocation kit we used was too big (actually, the Autozone one is too big too, with the top on, but that's easily resolved by not using the top).

If you're interested, I can post pictures of my install.

dakota · #3 (**permalink**) 08-23-2001, 06:33 PM

Thanks!! That's the way I was going to do it, but I had read one of the threads on this, and it was said to be sure to run a ground wire from the trunk mounted battery to the engine. I've never had a problem grounding each to the frame before, but I thought someone else may have had a problem doing it that way.

I got the battery dimensions now, but I would appreciate if you could post a picture of your install.

Thanks,
Wade

Double Venom · #4 (**permalink**) 08-23-2001, 07:49 PM

dakota,

We run almost every car with a trunk mounted battery. Here's the gist of what we have learned. If you want to do it by the book, then yes, the ground from the battery should run all the way back to the engine, especially if you are running EFI.

On a carbed motor it really shouldn't make that much difference.

It is also wise to use a flexible ground strap, available at NAPA etc., from the engine to the frame.

It's all about OHMS, and stuff that I couldn't explain if my life depended on it. (Have you ever read "Ohms' Law?)

If you decide to run it to the frame anyway, and one minute your car starts fine, and the next, the starter turns over like it's filled with molasses, or you find your MSD box isn't putting out enough juice to fire the engine, or maybe it just starts missing a little at high RPM..... suspect that "direct to frame from battery ground".

DV

jwinkler · #5 (**permalink**) 08-23-2001, 08:25 PM

OK, here goes - a test of uploading a pic of the battery:

and a pic of the cables going through the floorboard:

the outboard-most holddown bolt connection (viewed from under the car - this is the holddown that is behind the battery box pictured above:

and finally, the ground connection from the negative battery post - it sits on the frame rail almost directly under the battery:

I couldn't get a good picture of the motor ground strap, but it's a braided ground strap from the block to the frame rail right beside the ground for the starter.

FWIW, I haven't had any problems with this battery turning my motor except back when I was having the fan problems. The fan was wired in such a way that the thermostat could keep it running even after the ignition was off, so it would drag the battery down. If I tried to start it after only a few minutes, while the motor was still hot and the battery was weakened from running the fan, it would have trouble turning over.

JLW

dakota · #6 (**permalink**) 08-24-2001, 06:35 AM

Thanks guys. Wade

dalola · #7 (**permalink**) 08-24-2001, 08:21 AM

Wade,

Can you stand to look at some more titillating battery pix?

Thought I would offer you some more ideas. This is a DV built Cobra, with some of my own mods. I made a heavier hold-down bracket, and mounted a cut-off switch just in front of the battery. like J, I couldn't find a box that would fit in that cavity, and I didn't like looking at the exposed battery, soooooo I made my own cover out of corregated plastic and felt. I can remove it in about 5 sec., and the whole thing weighs about an once! The battery ground goes to the frame, like J's pic, and I put a braided ground strap on the engine to the frame. I've had no electrical problems at all, and the 10.5:1 460 cranks fine. Use the heavy 2/0 gauge cables, too.

Hope this helps, and good luck!

Dave

dalola · #8 (**permalink**) 08-24-2001, 08:25 AM

OK, how do you put more than 1 pic per post??? Grrrr....

Here's another...

dalola · #9 (**permalink**) 08-24-2001, 08:27 AM

OK, last one, I promise!

Jack21 · #10 (**permalink**) 08-24-2001, 08:31 AM

Side with DV on this one. I don't trust frame grounds, and tend to add redundancy. It'll start and run just fine initially, but as vibration and corrosion sets in, sooner or later you'll have problems. Steel also has more resistance than copper wire so some current loss will occur. Run a ground wire to the engine as a primary ground. Then run a ground strap from the engine to the frame.

I crimp, solder, grease, and shrink wrap all exterior electrical connections.

Dominik · #11 (**permalink**) 09-13-2001, 05:19 AM

jack,
just make sure that you crimp before soldering, because the solder has a tendency to float if pressure is applied (do not crip after soldering).

but you wrote it that way.

in addition to that i prefer to use a ground cable from the battery to the starter and make sure that it is thick enough.

i am not familiar with "gauge" as the indicator for the thickness, but if you measure the copper's diameter: 7/16" is plenty.

dominik