[Geoff]

Lots of people use the frame or body for the grd return....& have trouble free operation. Steel has 7 times the resistance of copper. So when the CSA of the steel is 7 times [ or more ] the CSA of a copper cable, the resistance will be the same...or less. The frame or body is not the problem. Poor connections or connections with insufficient contact area will add resistance. Also, starter motors come in different HP ratings. King of the Hill such as the MSD dyna force produce over 3.0 hp.

The fact that it cranks 'like a banshee' when cold suggests the cabling etc is ok. You may have a 'tight' engine that needs a higher HP starter. The starter may also be getting hot, internal copper armature winding increasing resistance from heat...& losing power.

[Sirrotica]

Originally Posted by Geoff

Lots of people use the frame or body for the grd return....& have trouble free operation. Steel has 7 times the resistance of copper. So when the CSA of the steel is 7 times [ or more ] the CSA of a copper cable, the resistance will be the same...or less. The frame or body is not the problem. Poor connections or connections with insufficient contact area will add resistance. Also, starter motors come in different HP ratings. King of the Hill such as the MSD dyna force produce over 3.0 hp.

The fact that it cranks 'like a banshee' when cold suggests the cabling etc is ok. You may have a 'tight' engine that needs a higher HP starter. The starter may also be getting hot, internal copper armature winding increasing resistance from heat...& losing power.

Your explanation of 7 times more resistance from steel conductors means that all your ground connections would need 7 times more surface area on the frame to carry the same amps.

I can almost guarantee that you'll have more voltage drop running through the frame than you'll have running the same distance through a copper conductor. Voltage drop also drops amps.

Next time you look at a truck with a power tailgate where the power has to run from the front of the truck to the rear bumper, take note if they run a dedicated ground wire, or just use the frame.

This isn't the first post on this forum that has a slow cranking engine with a body /frame ground, and a trunk mounted battery. A Pontiac with headers will really make the starter pull a lot of amps when hot, been there many times troubleshooting slow crank Pontiac engines. There's a reason the factory used a tin shield around the starter to deflect heat.

By using the frame, you also double the amount of ground connections from 2 to at least 4, more places to have problems with faulty ground connections. I believe in the KISS principle that the less to go wrong the better your chances are of being trouble free.

OP, you can take your pick with how to deal with the problem.