[Jimbobeast]

Originally Posted by Scarebird

Do you have a heavy cable from the frame to the block or better yet frame to the starter??

I ground the hell out of everything here.

I would also re-examine that heat blanket. Once heat soaked it is no good, worse holds heat! I would fab up a set of heat shields and use them. Air can still cool off the starter between the shield and starter.

Yes, same 00 wire from starter to frame. I can fabricate a nice heat shield and try it in place of the blanket. I do NOT have a ground from engine to frame except for the starter. Can't hurt to try that also.

[Sirrotica]

I've been through this decades ago in a 73 T/A. Don't try to use the frame as a ground, there is too much resistance in the steel that sucks up amps needed to crank the engine when hot. A hot Pontiac engine will need 4-500 Amps to spin over.

Run a negative cable all the way up to the engine same size as the positive cable attach it to a bellhousing bolt near the starter. It will crank plenty fast no matter how hot the engine or starter gets. Every configuration I tried using the car as a ground, failed when everything got heat soaked. Even with a commercial battery and a freshly rebuilt high torque starter (gear reduction mini starters hadn't yet been invented in the mid 70s).

That's my experience, and how I solved the problem, never had another slow crank after running a ground cable all the way to the engine.

[Jimbobeast]

Originally Posted by Sirrotica

I've been through this decades ago in a 73 T/A. Don't try to use the frame as a ground, there is too much resistance in the steel that sucks up amps needed to crank the engine when hot. A hot Pontiac engine will need 4-500 Amps to spin over.

Run a negative cable all the way up to the engine same size as the positive cable attach it to a bellhousing bolt near the starter. It will crank plenty fast no matter how hot the engine or starter gets. Every configuration I tried using the car as a ground, failed when everything got heat soaked. Even with a commercial battery and a freshly rebuilt high torque starter (gear reduction mini starters hadn't yet been invented in the mid 70s).

That's my experience, and how I solved the problem, never had another slow crank after running a ground cable all the way to the engine.

Now this might just work. Are you saying that the frame ground passes marginally enough current when the starter is cold but is insufficient whenever the starter gets hot and requires more amps?

[johnta1]

Yes he is.

[Sirrotica]

Originally Posted by Jimbobeast

Now this might just work. Are you saying that the frame ground passes marginally enough current when the starter is cold but is insufficient whenever the starter gets hot and requires more amps?

Exactly, Steel is a poor conductor for high amp draw situations. Also as ambient air temp increases on any conductor the resistance increases.

On the top 11 metals used for conducting electric, iron/steel is #9. It is also continually rusting due to the moisture in the air, causing conduction problems.

Stop and think about how your OEM battery cable system is laid out. The main negative cable is 99% of the time connected directly to the engine where the highest amp draw in the whole car is. Moving the battery to the trunk doesn't change that need to have the main negative cable connected to the engine where the highest draw is.

All the secondary grounds are run through the body because the amp draw can be supported by the body and frame, also because the engineers/bookkeeper's save running a separate ground wire to all the accessories. The body ground isn't done because it's the best type of design, it's to save cost on each car.

Also think if the last time you had lighting problems and how many times the whole problem is bad grounds through the body, or frame.

Think also about a snowplow with a electric pump on it, They don't use a body/frame ground to run that pump motor. They run a dedicated ground cable to the pump from the battery, same principle. It's not cheap to run a welding cable ground wire from the battery, but it does work............

I can just about guarantee you'll sidestep you slow warm crank problems with a dedicated ground from battery to engine.

[Shiny]

Originally Posted by Sirrotica

Exactly, Steel is a poor conductor for high amp draw situations. Also as ambient air temp increases on any conductor the resistance increases.

On the top 11 metals used for conducting electric, iron/steel is #9. It is also continually rusting due to the moisture in the air, causing conduction problems.

Stop and think about how your OEM battery cable system is laid out. The main negative cable is 99% of the time connected directly to the engine where the highest amp draw in the whole car is. Moving the battery to the trunk doesn't change that need to have the main negative cable connected to the engine where the highest draw is.

All the secondary grounds are run through the body because the amp draw can be supported by the body and frame, also because the engineers/bookkeeper's save running a separate ground wire to all the accessories. The body ground isn't done because it's the best type of design, it's to save cost on each car.

Also think if the last time you had lighting problems and how many times the whole problem is bad grounds through the body, or frame.

Think also about a snowplow with a electric pump on it, They don't use a body/frame ground to run that pump motor. They run a dedicated ground cable to the pump from the battery, same principle. It's not cheap to run a welding cable ground wire from the battery, but it does work............

I can just about guarantee you'll sidestep you slow warm crank problems with a dedicated ground from battery to engine.

This!