MG Sports Cars

engine swaps and other performance upgrades, plus "factory" and Costello V8s

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BOOTLEG
Gary Rosema
Wisconsin
(46 posts)

Registered:
11/18/2013 07:26PM

Main British Car:
1978 MGB Rover 3.5L

grounding ideas
Posted by: BOOTLEG
Date: December 18, 2016 07:44AM

Installing my Advance Autowire Harness and thinking about grounding. Considering 3 bus bars, 1 in engine bay, another in cabin and another in trunk. Would appreciate ideas from others


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5354 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: grounding ideas
Posted by: BlownMGB-V8
Date: December 18, 2016 08:04PM

You're on the right track, it's hard to have too many grounding locations. If you run efi it gets even more interesting.

I have the following: Heavy ground cable (00) from the battery to the transmission tailshaft housing. #6 or 8 cable from the battery to the body. #6 or 8 cable (and power) from the battery into the trunk to 3/8" terminals. Separate #10 stud for ground terminations in the trunk including lights. Two #10 studs under the dashboard. At least two #10 studs under the hood plus an additional #10 stud with a ground lead that runs directly to the battery ground post for sensor grounds.

It isn't too many.

Jim


ruben
rick maroni

(6 posts)

Registered:
04/22/2017 01:32AM

Main British Car:


Re: grounding ideas
Posted by: ruben
Date: May 02, 2017 01:14AM

Your not grounding you are bonding the car body parts together. If the engin is effectively bonded to the body the resistence between any point not inhibited by corrosion or paint and the negative battery post should be zero. I don't see how a ground buss can offer less than zero resistence. It is how the connections are made to the body and paint does cause resistence to current flow. And induced voltages in the sub mA range that may effect electronic will not be drained off by a ground buss. An insulated positive connection in the engine commpartment is useful so all the positive wires don't
have to connect at the starter or alternator. Good Luck



Edited 2 time(s). Last edit at 05/02/2017 06:32PM by ruben.


Jim Stabe
Jim Stabe
San Diego, Ca
(603 posts)

Registered:
02/28/2009 10:01AM

Main British Car:
1966 MGB Roadster 350 LT1 Chevy

authors avatar
Re: grounding ideas
Posted by: Jim Stabe
Date: May 02, 2017 01:53AM

Actually, steel has far greater resistance than copper, certainly not even close to zero. At least ground the high current devices (starter, fans, etc) with copper of the same gauge as the feed wire back to the battery.


Charles
Charles Long
McDonald, TN
(148 posts)

Registered:
09/15/2013 08:54AM

Main British Car:
1966 MGB V6 1994 Camaro 3.4L 60V6

authors avatar
Re: grounding ideas
Posted by: Charles
Date: May 06, 2017 09:45PM

My 2 cents. Like the two Jims said.
The material used in the body construction of our old British Cars was at best very poor then, when it comes to the conduction of electrical current. Now some 50 or more years later and with the added rust it has gotten no better.

With the electrical currents demands we are placing on the materials used when constructed is only asking for electrical issues.

I personally do not use any part of the car body for grounds. I only use the body material as a tie point.

Of course my working back ground in the medical field, my have something to do with my lack of acceptance of a voltage drop across any tie points.

charles


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5354 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: grounding ideas
Posted by: BlownMGB-V8
Date: May 07, 2017 12:03PM

Yeah, what those guys say. You can look up the conduction capabilities of metals and here is a chart that is rather illuminating:

[en.coppercanada.ca]

If you look at it you'll see copper referenced at 100%, silver at 106% and gold at 72%. (Silver is best but tarnishes while gold does not.) Iron is at 17% of the conductivity of copper. Now that seems extreme but I believe if you look at the actual resistances you will find it correct. As the following table shows, iron has nearly seven times the resistance of copper:

[www.teach21.org]

So that's what you are using for your grounds. Why? Because early days, currents were gross and components inefficient and it just didn't matter. Things have changed a bit.

Jim


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