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Length of the cable will also effect how well it works.

If you get a chance, see how warm the cable is after a run.

I assume your referring to the alternator charge cable ? not the main starter motor cable ?

yeah, charge cable only. It's a long run with the isolator been at the rear of the vehicle.

The standard size cable in the factory V6 loom is marginal at best. Plenty of threads on JC with burnt out cables over the years. I think Holden probably spec'd the cable to handle average load only and not peak load.

In your case you probably don't need to include the thermofans and head lights in your load calculation for when your heading down the strip.

can you run 2 alternators, one extra one where a/c mounts and use that for your other stuff on separate loop even.

well my charge cable is probably not as big as a commodore one!

as far as 2 alternators, i'll go a single 120amp before I mount a second one

If its getting down to 11v under max load then that makes me think the power cant get from the battery to the front of the car. If the alternator wasnt keeping up then the battery should make up the difference to keep it at at least 12v until it goes flat. If you cant get fatter charge wire, can run 2 of the same.

The JAycar catalogue has the following listing

8ga cable outer daimeter 6mm, core 8mm­2 rated 56A
4ga cable, outer diameter 10mm, core 20mm2 rated 110A
2ga cable, outer diameter 12mm, core 35mm2 rated 160A

What I'm not certain about is if that outer diameter includes any insulation.

I think the standard Commodore V6 alternator cable is similar (if not smaller in size) to a 8ga cable.

Considering the length of the cable run, err on the larger side.

i've just had a look, i have 8ga cable to my LS2 coils, thats 60amp according to the part number on jaycars website, and the cable to the alternator looks to be slightly smaller!! it doesn't have any labelling on it though so i am going to say its at the very best probably going to be 50amps!

might be time to go and procure some 4gauge that should fix it hopefully!

and looking at the 8ga i have and a stock commodore wire i would say your probably right with it being about an 8ga

The current rating is not really what you want to look at in this case. While a '50A' cable could carry more over a short distance and have no problem, the voltage drop becomes significant over the distance you have to run it. Losing near on a volt over the cable becomes an issue for charging a battery!

Some quick calcs using some wiki cable resistances at 50A over a 6m distance, 8ga loses around 0.6V, 4ga loses 0.2V. At 80A its 1V and 0.4V.

Not all cable is created equal either, look out for the rubbish cable with a heap of insulation to make it look like thick cable.

Moving the sense wire to the battery or putting a diode inline with the sense wire can help if its still a problem. A diode increases the charge voltage by around 0.7V.

I will replace the cable with a larger one anyways cause I am pretty sure I am not even running the same capacity as the commodore had stock, so if nothing else I should be aiming for the same or larger ..... the sense wire is a question I can't answer, I know I had a thought of running it to the back of the car but I am not sure if I actually did it or not lol! so will make sure that is the case aswell and then see if the issue is still there or not.

thanks for all the info and advise people!