Engine ground straps

[EZ$]

I'm trying to tie up the loose ends before the engine gets installed, and I was wondering if I could use a #4 cable as a strap, one on each side of the block, instead of a traditional ground strap? I'm using #2 battery cables, and I'm just trying to avoid another purchase, no matter how small, if I can avoid it. Will this work?

Rick

[Jeff Kleiner]

Remember that the entire system is only as good as the weakest link---in other words if you have #2 cables on the + side but #4 for ground the starting circuit is effectively a #4.

Jeff

[Papa]

Rick,

You should have a large engine to chassis ground strap in the kit. I don't recall what gauge it is rated at.

Dave

[JohnK]

Jeff, I don't fundamentally disagree with what you're saying, but there are a couple of other factors that come into play. First is cable length. If the + side is 8-10 feet of #2 but the ground side is 2 ft of #4, then it's a bit closer. Adding to this is that the OP is talking about two #4 ground straps in comparison with a single #2 positive cable. Overall, I don't think it would be a problem, but I've never been accused of being an electrical expert.

[NAZ]

If you use two #4 you should have a large ampacity margin over a single #2. Do an internet search of cable ampacity to see for yourself.

[mike223]

Adding to this is that the OP is talking about two #4 ground straps in comparison with a single #2 positive cable. Overall, I don't think it would be a problem, but I've never been accused of being an electrical expert.

I have been at least accused of it (+ ocd to boot, lol)...

I ran #2 to the block from the battery (grounded the battery to the frame close also with #2).

2 #4s will probably carry more amperage than 1 #2 (but not ocd enough to look it up).


But trying to ground the *lead post* battery, through the #2 copper (with connectors of some sort), to the steel frame, and then picking up 2 #4 copper (with connectors of some sort) to the engine block...

Simply introduces a lot of potential (hard to put your finger on, grounding) failure modes.


If all your connections are clean + greased - you're ok.

As soon as one of them fails - go track it down - good luck.


From fingers + eyes that have hunted a lot of grounding (+ other) failures (sometimes it takes days to put your finger on it).

[Jeff Kleiner]

Sorry guys, I missed that he intended to use a pair of #4 cables and not just one. As I've said before, comprehension is sooooo overrated...

Jeff

[Richard Oben]

Batter cables are pretty cheap in the scope of this project. One at battery and one at engine, if this is causing you financial issues, you may want to rethink the project. JMHO. Richard. PS been building these cars since 1998.

[Al_C]

My suggestion, for whatever it is worth:

[JohnK]

Cable ampacity aside, Al_C's photo got me to wondering why bare flat-braided cable is used for ground straps. A quick google search suggests that this is because these are more flexible than regular shielded cable, and will resist road and engine vibration better. Not sure if there's truth to this, or if this is just done nowadays because it's a customary practice plus internet folklore. So, assuming that two #4 cables could handle the load from an electrical standpoint, is there a problem with using a shielded cable as a grould strap instead of a bare flat-braided ground strap?

[BEAR-AvHistory]

Agree with Al_C. Have a few flat braided ground straps on the car. No grounding issues so far. Very cheap insurance.

[EZ$]

Jeff, I was concerned when I read your first response, and relieved when I read your second. I respect your opinion. As a note, the battery has a #2 wire grounded about two feet from the battery.

Dave, Unfortunately, this was a Base Kit, so no ground wire. My timing was perfect on my purchase, I ordered just prior to F5R coming out with the FIA kit, so I've gotten to source all the parts that would have come with the kit on my own, YEAH!

JohnK, That was my thought process on this, but I too have never been accused of that either!

NAZ, Thanks.

Mike, I think I get the idea you're talking about, but I was thinking along the lines of what Doc said in his reply on the other forum, "you can't have too many grounds". When you say "clean and greased", are you talking about coating the ground connections with dielectric grease to keep them from corroding? If so, I guess all the ground point connections should be treated that way. Correct?

Richard, As with Jeff K, I really respect your opinion, and I understand the relatively low cost of the straps, but as I've added all the low cost items I've needed for the build, they've become a major outlay of cash. I'm just trying to find out if I can use parts that I already have. Oh, and believe me, I have rethought the project many times.

Al, I appreciate your suggestion, and I will end up going this way if my idea won't work, but if it will work, I want to use what I have here already.

JohnK, I was wondering the same thing.

Thanks everyone.

Rick

[NAZ]

Automotive ground cables typically come in two varieties. The shielded kind same as the hot but with a black insulation and the braided flexible type. I mostly use the shielded type but I've used both in the past. I have the tools for crimping larger cables so I find it easier to use this type and get the exact length I need.

[mike223]

Mike, I think I get the idea you're talking about, but I was thinking along the lines of what Doc said in his reply on the other forum, "you can't have too many grounds". When you say "clean and greased", are you talking about coating the ground connections with dielectric grease to keep them from corroding? If so, I guess all the ground point connections should be treated that way. Correct?

Short answer is yes - dielectric grease on all the connections.


"You can't have too many grounds" - true, but let me give you an example of my thinking on this:

1- Every connection, both wire to connector (crimp) and connector to termination increases your resistance slightly - lots more resistance if it's loose or corroded, etc.

2- Steel doesn't conduct electricity as well as copper - I like running a full size battery cable (#2 in this case) all the way from the battery to the engine block because of this.

3- Amperage rating of #4 wire is ~125-200 amps, Amperage rating of #2 wire is ~170-240 amps, Your starter is pulling ~400-800 amps - this is why you can't crank the starter for long, melts down starter + cables + battery.


So let's imagine you go from the battery to the (steel) frame (-) and starter (+) with #2 cable, then ground the block with 2 #4 wires to the frame - count how many extra connections you've added, as opposed to running #2 from the battery to the block. Add in the additional resistance of running through the steel frame.

When you crank the starter you're already way past the rating of all the wires you've run - what happens if one of your #4 connections (wire to connector, connector to steel or cast) isn't all it needs to be? Or your ground strap(s), pick your poison.

Electricity takes the path of least resistance, and in this case some of it is almost certainly going to move through your antifreeze to the radiator to the frame.

And that is a textbook case of how to induce galvanic corrosion in your expensive aluminum radiator (think pinholes).


That's why I run #2 welding cable all the way from the battery to the engine block - it's really just cheap insurance that eliminates a lot of different potential faults / failures.

[EZ$]

Thanks Mike. That actually made a lot of sense to me. Usually it takes a 2x4 to get that much info into my brain!

Rick

[frankb]

Rick:

"Dielectric" grease is actually an insulator (used to mount electronic components to heat sinks) and should not be used in mounting your ground cables. Just use regular grease to prevent corrosion.

Frank B

[mike223]

All greases are lousy conductors - that's not what it's there for.

https://dielectric_grease_vs_conductive_grease.htm