#41  
Old 02-01-2025, 02:31 AM
Geoff Geoff is offline
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The factory battery-to-frame ground is there to ground components that are connected to the frame. Such as the horn button via the steering box.
If you are going to use the frame for the grd return for a trunk mounted battery, I would bolt the cable to the engine mount. It keeps the cable length short & direct.

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  #42  
Old 02-01-2025, 09:01 AM
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HWYSTR455 HWYSTR455 is offline
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Yup, I use one of the unused engine mount holes in the block.



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  #43  
Old 02-02-2025, 01:33 AM
Geoff Geoff is offline
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I am blaming my comments in post #41 on a seniors moment.....
The info in post #41 works for the battery in the engine bay.

Of course, this thread is about a trunk mounted battery...

With a trunk mounted battery, bolt the grd cable to one of the bellhousing bolts, lower bolt to keep cable as short as possible. Leave a small loop in the cable to allow for movement/vibration.

  #44  
Old 02-02-2025, 09:12 AM
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I'm on board with using the bell housing ONLY if you make sure the contact(s) are not compromised by paint.

An engine mount bolt/bolt (block side) hole has less chance of being compromised in that way.



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  #45  
Old 02-02-2025, 10:35 AM
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george kujanski george kujanski is offline
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A word about the role of a battery.. it also provides electrical noise filtering in the electrical system, but in order to do that, the cabling between the battery and the system has to be low impedance and low inductance, i.e. short and good cable. On modern systems with various sensors, the sensor grounds are right at the engine metal with short connections from the engine metal to the battery. This eliminates ground loops, i.e. where ground points have different voltages compared to the battery negative. Ideally, there should be zero voltage difference between the battery negative and any other ground.

A short story... when I worked at Motorola Charging Systems, we provided systems to Volkswagen of America. and had to meet charging specs for various models. Some had batteries under the hood, some under the rear seat, and some in the back of the vehicle. The voltage regulation was slightly different due to noise present at the regulator due to cabling differences. We proposed that a standard cable setup was to be used for testing to provide consistent results.

George

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Old 02-02-2025, 01:17 PM
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Good advice and understand. Quality cables are a must.

My engine ground to frame is @ 12", and my frame to batt is about the same.

My ALT ground is about 8", which connects to the same point on the engine as the frame ground.

I have a ground that goes from the frame right next to the body mount to the body, both with riv-nuts.

I have one ground from the back of engine to the firewall with a riv-nut.

One more ground goes from the frame to the junction of the inner & outer wheel housing, all riv-nuts.

Also have a core support to frame by the batt, both w riv-nuts. At the core support junction where the ground meets the core, I ran a wire over to the fender. Overkill, but fine by me.

Basically, the entire left frame rail is a ground (on the GTO). The body has those 3 mentioned ground points on the frame. Frame has been blaster and powder coated, another reason for the riv-nuts.

For the passenger compartment, the lower dash rail is the ground for everything in the dash, and from the driver's side lower dash rail mount, it's inches from the body ground-to-frame point.

All but one frame grounds are 6AWG, the ALT-block-frame-batt run is 2AWG (maybe 4AWG, would have to actually check, but pretty sure it's 2AWG).

On the bird, being a unibody, I will run a dedicated ground the length of the car on the driver's side, with 4 mount points along the way using riv-nuts. Will use the dual-cable batt terminals.

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