Battery, starter, and alternator wire gauge and feedthrough.

Hey all,

I'm rewiring my car and plotting things out. The battery is in the trunk, it's a normal AGM battery. The engine is a GM LFX (3.6l DI V6) which is known to be finicky about starting with low voltage due to DI fuel injectors. The alternator is rated for 120A, it's a one-wire TuffStuff unit.

I'll have a single firewall passthrough, possibly a stud, so that on the cabin side I can have the cable from the battery to the feedthrough, and a cable from the PDM to the feedthrough. Then on the engine side, have the cables to starter, the cable to alternator, and possibly ABS and EPS cables as well.

Have any advice on wire sizing and feedthrough options? A Surlok would be nice, but then. I'd have to have a spliced/branched power cables?

Thanks

Dan,

I am in the process of redoing a replica cobra. Trunk AGM battery, about 8' of cable from the battery, thru the disconnect to the solenoid to the starter. It was originally wired with #2 cable and I am experiencing some major voltage drops as the starter does its thing. One of the steps to help resolve this is to change the positive and negative cables from the battery to 2/0 cable to reduce any potential voltage drop. I also don't rely on the frame for the ground, I run a cable from the negative to a stud near the starter, then a flex strap from the stud to the stater mounting bolt.

A direct path on the negative is as important as the positive path. 2/0 is twice the area of #2 cable and conductor area figures into the resistance equation.

Paul

I would at least run 1/0 from battery to starter and as stated above from battery negative to block.. the block to chassy... then you can run a 4ga from starter to the 12v pass-through. Then you'll have the cabin side to branch out to the pdm and to feed the other 12v.

What ecu and pdm are you using?

+1 for Paul's comment on the ground being as important as the positive path since that's very often overlooked, and I diagnose far more ground side issues than power side ones.

I'm running an AiM PDM32 and the stock GM ECU (E39A). The car currently has a 0awg cable from the battery in the trunk straight to the starter from the original battery relocation project. I was hoping to keep that cable for the battery to firewall run, but could upsize I suppose.

I understand the importance of the ground path but.. is the chassis really insufficient if the connection to it is proper? it is all steel with no adhesive bonding like a modern aluminum chassis. I could weld a bolt/stud to the chassis near the battery for a good bond potentially. And maybe also in the engine bay to ground the block. I guess I'm trying to avoid the weight and bulk of a second battery cable run, but maybe it's not terrible.

Because it's a relatively short run from the firewall to the starter, I was thinking 2awg. Then 4awg from that same point on the firewall to the alternator. I I can more easily clear the headers by running alternator from firewall to alternator instead of jumping from the starter. What do you think?

Thanks!