Battery in trunk

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tony20110

tony20110

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Hi everyone. I have a 360sb in a 1966 Barracuda and I recently moved the battery to the trunk. I am not getting enough juice to turn the engine over. I’m not sure if I need a more powerful battery or what my options are. Any advice would be greatly appreciated.
 
You may be getting enough voltage to the starter but not a strong enough ground. Its a common problem with trunk mounted batteries.
 
@crackedback has a real nice trunk mount battery wiring diagram. That's the only way I'g go if I was doing it. Maybe he will chime in and post it.
 
Sure sounds like a crappy ground to me.
Ground the battery to the chassis, not some handy bolt in the trunk or trunk floor. And a good ground directly from the block to the frame. Those are step1 and step1A.
And of course, you need nice large cables with fine wire. I use welding cable and fab the ends. 2 gauge or 0 gauge.
 
You talk frame to frame on the ground but with the unibody frame to frame is useless. When the frame ends the floor pan now picks up the ground. Unless you connect the front and rear frame with a wire, there really is nothing to be gained.
 
tonysrt said:
You talk frame to frame on the ground but with the unibody frame to frame is useless. When the frame ends the floor pan now picks up the ground. Unless you connect the front and rear frame with a wire, there really is nothing to be gained.
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.....or if you have welded-in subframe connectors and elephant ears, like I do.
 
tonysrt said:
You talk frame to frame on the ground but with the unibody frame to frame is useless. When the frame ends the floor pan now picks up the ground. Unless you connect the front and rear frame with a wire, there really is nothing to be gained.
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Boy is that ever a wrong answer. The frame rails are tied into the rockers. If I have to explain that further, there's really no use.
 
And aren't the rockers just like the floor pan? Made out of thin gauge steel.
 
tonysrt said:
And aren't the rockers just like the floor pan? Made out of thin gauge steel.
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It's all sheet metal. But the rockers, like the frame rails are thicker gauge metal and bent to be very strong. So the chances of a bad connection going to the frame rail instead of just to the trunk floor are much more slim. The inner and outer rockers ARE basically frame rails. I can tell you've never had them apart.
 
The whole body becomes a ground, roof, rockers, frame, floor etc.. Attaching the ground to the frame just gives you a nice thick attachment point.
 
273 said:
The whole body becomes a ground, roof, rockers, frame, floor etc.. Attaching the ground to the frame just gives you a nice thick attachment point.
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Yes, exactly my point. But we've ALL seen things that defy the laws of physics, like a spot on the floor pan or trunk pan that might have lots of resistance. I mean, why chance it?
 
tonysrt said:
And aren't the rockers just like the floor pan? Made out of thin gauge steel.
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Even say the ground just traveled through the floor, it maybe thin but it's also 5-6' wide, nevermind the roof, doors, rockers etc..
 
RustyRatRod said:
Yes, exactly my point. But we've ALL seen things that defy the laws of physics, like a spot on the floor pan or trunk pan that might have lots of resistance. I mean, why chance it?
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I'd want the attachment point to have similar thickness as the wire.
 
273 said:
I'd want the attachment point to have similar thickness as the wire.
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Exactly. And as I said, we've all seen rust, corrosion and dirt get between welded seams, especially a single thickness thick. It's just smart to locate the ground on the thickest point possible. I also use 1.0 gauge whenever I relocate to the trunk. In fact, I have 1.0 on my truck with an under hood battery and I plan to put them on Vixen, too.
 
Besides an ground from the engine to the frame I'd put a couple of ground straps to the firewall that way if one connection becomes faulty the others will make up for it.


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And this is why it is a good idea to connect front and rear frame rails with a solid connector, I had a 1x2 steel boxed rail welded to front and rear rails which also adds to rigidity.
 
tonysrt said:
And this is why it is a good idea to connect front and rear frame rails with a solid connector, I had a 1x2 steel boxed rail welded to front and rear rails which also adds to rigidity.
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The floor say is 16 gauge .0625" and the floor is 5' wide that's equal to 3.75" sq that's like 12, 0 gauge cables connecting the back and front. It would take a **** ton of electricity to turn the mid section of your car into a fuse. There's more than enough metal connecting the front and back of your car to start it. Just needs good grounds on both sides.
 
If you want to use the body for the ground connection for the bat in the trunk, then there is no problem with that electrically providing the connection points are good.
But what is the benefit? You are adding weight because a THICK [ heavy ] copper cable is needed for the positive. If it is for weight transfer, is it worth it?
 
Bewy said:
If you want to use the body for the ground connection for the bat in the trunk, then there is no problem with that electrically providing the connection points are good.
But what is the benefit? You are adding weight because a THICK [ heavy ] copper cable is needed for the positive. If it is for weight transfer, is it worth it?
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I don't have the wheel scales to prove it, but I believe it is. I grant a nice big cable has some weight, but it's low on the chassis, and pretty close to equally weighted on front and rear, maybe slightly biased to the rear.
And I think if you move a 27 from extreme front left of a (for example, rr) car, to extreme right rear, you have helped traction on the lift side of the rear end physics reaction, and I would bet at least a two percent weight distribution improvement. On my light car, it amounted to almost four percent. Anything I could do to help the 60/40 distribution I had, I was gonna do.
 
Taking 3-4 pounds of cables out and put 8-10 in. A whopping 5-7 pounds if using 1/0 welding cable like I use. Go on a diet! I guess if you are a stock or super stock racer looking for every hundredth, that might be important. My favorite was a car that ran faster et/mph with two batteries in the trunk instead of one.
A street beater. Not a chance you'll ever notice the weight. Throw one of those acme anvils in the trunk ala Wiley Coyote

Run a ground to the frame rail in the rear and another from engine to frame rail up front.

For the OP, take a set of jumper cables and run from the bat neg to the block up front, see if the car starts easier. If it does, part of the issue is your ground path. Hillbilly diagnosing.
Grounds need to be same size as positive cable.
 
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crackedback said:
Taking 3-4 pounds of cables out and put 8-10 in. A whopping 5-7 pounds if using 1/0 welding cable like I use. Go on a diet! I guess if you are a stock or super stock racer looking for every hundredth, that might be important.
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tuning program by slimfast!

i wouldn't be the slightest bit worried about adding 20~30lb to a street car. if you're competitively racing for money where hundredths count, different story.

dudes be out there: i need to be as light as possible and i need another 100hp to knock a few 10ths off. drop 50~75lb and take the $$ you were gonna drop on mas HP and put that into better tires or chassis tuning/mods and betcha that picks up half a second instead.
 
crackedback said:
Taking 3-4 pounds of cables out and put 8-10 in. A whopping 5-7 pounds if using 1/0 welding cable like I use. Go on a diet! I guess if you are a stock or super stock racer looking for every hundredth, that might be important. My favorite was a car that ran faster et/mph with two batteries in the trunk instead of one.
A street beater. Not a chance you'll ever notice the weight. Throw one of those acme anvils in the trunk ala Wiley Coyote

Run a ground to the frame rail in the rear and another from engine to frame rail up front.

For the OP, take a set of jumper cables and run from the bat neg to the block up front, see if the car starts easier. If it does, part of the issue is your ground path. Hillbilly diagnosing.
Grounds need to be same size as positive cable.
Click to expand...
I did exactly what @crackedback recommended. Ground cable comes off the battery and goes straight down through the trunk floor to the right rear frame rail. That cable can't be more than 14" or so. Then a same size cable from the right rear cyl head to a nut welded to the right front rail. Again, not very long. And I used either 2/0 or 1/0 welding cable (can't recall) for the positive side...of course through a Ford relay to keep it dead except during crank.

With a mini-starter, the avatar's 10.5 CR 408 will crank like crazy if need be although it normally starts almost instantly. I give @crackedback the credit for my setup!
 
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