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Old 06-25-2020, 01:34 PM   #1
Tempest67
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Grounding Straps/Wires for motor

Hi Guys,

I am just completing the new wire harness install (carbed SBC in a 51 on a S10 frame) and was thinking about grounding straps.

Typically, I see a small ground wire (copper about 1/4 inch wide and 6 inches long) from the back side of a head to the firewall, and then sometimes a larger ground strap (copper about 1/2 inch wide and maybe 9 inches long) from the block to the frame.

Are 2 grounding straps enough?

what do you suggest?

Thanks for your help
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Old 06-25-2020, 02:09 PM   #2
mongocanfly
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Re: Grounding Straps/Wires for motor

I like to use as many grounds as possible....well sorta...battery to engine..engine to frame..engine to cab..and. cab to frame..most of the time electrical issues are ground related...I also have one from the bed to the frame...
May be overkill but they are cheap Insurance
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Old 06-25-2020, 02:43 PM   #3
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Re: Grounding Straps/Wires for motor

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Originally Posted by Tempest67 View Post
Are 2 grounding straps enough?
not in my book. i used #0 welding wire from battery to a stud on my frame, then i added a separate wire to the body, 2 stereo amps and motor

those little ground straps are insufficient. on a cold morning your starter uses everything the battery can throw at it, this will be well over 200 amps. at a minimum you want a heavy cable from battery to motor. then you want an #8 min to the frame and the body. additional grounding if you do a big amp or 2.

don't use house wire, it it very stiff and has very few strands compared to welding wire or automotive wire
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Old 06-25-2020, 03:45 PM   #4
28TudorAZ
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Re: Grounding Straps/Wires for motor

Here is what I used.
https://www.amazon.com/Standard-Moto...114317&sr=8-16
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Old 06-25-2020, 03:57 PM   #5
Tempest67
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Re: Grounding Straps/Wires for motor

Thanks Guys,

I will add several
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Old 06-27-2020, 10:35 PM   #6
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Re: Grounding Straps/Wires for motor

you could count on the chevy 350 starter drawing in the neighborhood of about 250-350 amps depending on the starter used and the performance level of the engine.
for a 250-300 amp draw over a max 4 ft length you need a 4ga cable minimum. welding cable is great because it is more flexible due to the number of strands. a starter/alternator repair shop should be able to fix you up with the cable with the lugs pressed on and shrink tubed for a good price. I am not a fan of the cheaper cables that a lot of auto stores sell, they don't flex well because they have less strands plus the insulation used is also less flexible when you go to strip the cable for a terminal install.
I like to use a ground cable from the battery to the engine block and one from the block to the frame, large cable. a smaller cable should go to the body depending on what the amp draw of the accy's used will be. longer cable runs mean larger cable to handle voltage drop over the length.

https://www.crutchfield.com/S-BnuZ5p...uge_chart.html
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Old 06-28-2020, 05:08 PM   #7
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Re: Grounding Straps/Wires for motor

Good clean bare contact areas for ground cables is a must. I've gone out and checked on a couple of won't crank good situations on freshly assembled rigs where the owner had so may coats of paint on the engine or frame under the ground strap that there was little or no electrical contact. One actually had a fit when I scraped away the paint under the ground cable on his engine that must have had six coats of paint on it to get to bare metal to get a ground.

Cable size, think of an electrical cable in the same respect as a water hose and voltage in the same respect as water pressure with amps equaling water flow at the end of the hose.

You are only going to get so much flow though a certain size hose as the hose allows. Same with a wire or cable the wire or cable will only carry the amps it is sized for.

I had trouble with my 77 Dualie because a previous owner had put the smallest diameter battery cables available in that length on it and they just didn't have the capacity to crank a 454 when it was hot and the starter was hot. Parts house actually had the larger cables they just cost more.

I agree that you can't have too many ground connections between major pieces on the truck though. Depending on how your setup is Ground cable to either frame or engine block, strap between frame and block, strap to cab and strap to the bed to ground lights that are grounded to the bed/box.

Old school woven straps or short proper gauge cables with ends is up to individual taste.

When I worked in the Pontiac Dealership in Waco Tx in the mid 70's we would get a lot of Grand Prix and Lemans in with the floor shift cable for the automatic frozen up. Invariably someone had replaced valve cover gaskets or valve covers and hadn't connected the ground straps from the firewall to the valve cover bolts back up. When they were left off the only ground for the body was the floor shift cable.
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Old 06-29-2020, 12:25 PM   #8
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Re: Grounding Straps/Wires for motor

Thanks for the advice, that is the help I was looking for.

I will post pics when completed
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Old 06-29-2020, 01:41 PM   #9
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Re: Grounding Straps/Wires for motor

do yourself a favor, especially if you have aluminum heads or even an aluminum water neck, run ground wires from the heads to the block and then to your ground on the battery or frame. 90% of the electricity in the car is in the ignition (spark plugs, etc)
if you don't that electricity will find a ground path somewhere and it usually is not pretty. I have seen it turn throttle cables into toasters, completely erode water necks, it acts just like a EDM machine if you don't give it a easy path.
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Old 06-30-2020, 04:00 PM   #10
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Re: Grounding Straps/Wires for motor

Quote:
Originally Posted by 28TudorAZ View Post
I think those old-style tractor braided ground straps are cool.

Quote:
Originally Posted by jwhotrod View Post
do yourself a favor, especially if you have aluminum heads or even an aluminum water neck, run ground wires from the heads to the block and then to your ground on the battery or frame. 90% of the electricity in the car is in the ignition (spark plugs, etc)
if you don't that electricity will find a ground path somewhere and it usually is not pretty. I have seen it turn throttle cables into toasters, completely erode water necks, it acts just like a EDM machine if you don't give it a easy path.
Once I was doing some welding on a project car and accidentally forgot my ground clamp and left it laying on the car. After the welding was done and I realized my error, I calculated that the current had actually gone through the rear end and back up the driveshaft to the engine and then the frame. Yikes.
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Old 06-30-2020, 05:08 PM   #11
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Re: Grounding Straps/Wires for motor

a young welder's mistake I have seen is when working in Ft Mcmurray in the cold of winter the welders would weld on an extra lump to the grouser bars on the track pads of the dozers. this is for traction on ice because a dozer pad is fairly flat so going ahead and back the tracks will rather spin out instead of grip plus they can be slid sideways fairly easily on ice, like skates, if it is a side hill so the extra lump in the middle of the track pads helps stop or slow down the process. anyway, the dozers are put up on stands and the welder welds on pieces a few inches long onto each track pad, staggered so they don't all line up in the same footprint as the track spins around. long story short the inexperienced welders sometimes are not told to place their ground on each pad as they weld, instead of on a single pad for the whole job. if they don't do it right then welding current will pass through the bearings in each chain link of the track and leave a mark so the track wears out in fairly short order after the grouser bars are welded up. same goes for welding on vehicles if welding on something place the ground close to the weld, on the same part preferably, to eliminate the current flowing through something else first before making it's way to the weld
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