remote battery woes
 

Back in '97 my red 70 GTO convertible was a show car. The trunk was painted body color and the battery and starter solenoid were moved back there. It looked neat. When cold, the starter spins like a banshee. When hot it barely turns over the 455 block. The battery and starter are both grounded directly to the frame, all starter cables (including the long run from the trunk to starter) are I believe 2-0 gauge (maybe 2 gauge?) - really thick with professionally applied terminals. The starter is an aftermarket high torque mini-starter with an asbestos type heat blanket. I have exhaust manifolds, not headers and they run close to the starter like a stock engine. The battery is new-ish and has a zillion CCA.
What else can I do to improve the embarassing hot sluggish starter problem (besides putting the battery back in front).

AWG 2 gauge wire (just the metal, not including the insulation) is just a bit over 1/4". AWG 00 (2 ought or 2-0) is just a shade under 3/8".

What Scarebird said.


The engine needs a big/good ground to the frame, plus body to the frame.
I usually run 2 cables from trunk to engine, 1 ground and other the positive.
(Firebird, no full frame)


:)

00 definitely

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.

Which mini starter are you using?
I installed a Jegs 1.4kW (~1.9hp) rated denso style starter for my 455 and it struggles when warm I suspect it may need need new solenoid contacts after 14 years of use but it wasn't that great when new. I'm considering getting a 2kW (~2.7hp) upgrade in the same style but would like to know your type first.

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.

I would put the battery back in the factory location.

I used to have a 1964 GTO that I bracket raced, I put the battery in the trunk. I used 2-0 welding cable for the positive that ran through the frame rail and also utilized a Ford solenoid for sure starting, the battery was grounded to the frame using 2-0 cable as well. I also grounded the body to the frame with a copper strap and grounded the engine to the frame with 2-0 cable, I was using a Pontiac starter nothing fancy.

After racing the car for over a decade with no starting issues ever I decided to quit racing and returned the car to the streets. I moved the battery back to where it belongs, under the hood. Easy access and just better all around if you need to charge the battery or jump start the car.

I pulled probably 20 pounds of 2-0 cable out of the frame during the process. When I was drag racing the car I did whatever I could to get weight off the front end, relocating the battery, removing the front inner fenders, some of the bumper bracing, heater and wiper assemblies etc. I put everything back on the car to make it comfortable again and putting the battery back up front just made sense.

I really can't remember the brand of starter presently in the car and my RAIV car is currently on the lift, but I will look through my receipts.

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?

Yes he is.


:)

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............:thumbup:

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

This!

00 cable from battery to engine it is!

For a show car I dont know why you would move the battery to the trunk?If judged im sure it would result in loss of points.Tom

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. :noidea:

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.

Nope.
You are assuming that the frame resistance is only 7 times the CSA of a copper grd cable, when in reality, the CSA is much more than 7 times. If the frame was 14 times the CSA of an equivalent copper cable. the frame resistance would be half that of a copper cable, with a corresponding reduction in the voltage drop [ loss ]. The connecting lugs are nearly all copper, but tin plated. There are numerous resistance points in the starter cct, both on the neg & pos side which add to the total res in the cct.
If you had a copper cable for the grd from the battery in the trunk, it will heat up from the current draw during cranking. Because copper is a good conductor of heat, it heats up very quickly...& it's resistance increases....& causes more voltage drop. Using the steel frame as the grd, it heats up much more slowly because it is a poorer heat conductor than copper & will have less voltage drop than the copper cable. It is the sum of all the voltage drops in the cct that reduces the final voltage that the starter sees.

OK, I guess...huh?
So, if the CCA's are more than the CSA's then the total neg and pos res in the cct could be 7 or 14 times the res of copper unless I cut the frame in half and pre-heat a tin shield that is grounded 4 or more times.
Yes, it is all clear now. :-)
I think I will first try a dedicated 00 cable from battery to starter ground, then if that does not work a MSD Dynaforce starter with heat shield (maybe minus the insulating blanket).
The car is a modified 1970 GTO convertible, 462 CI, 6-speed, 4-wheel discs, fuel injection, etc., hence the battery in the trunk for looks. It took 1st place in concours modified at the 1997 GTOAA convention in Atlanta.