im not sure on the thickness.. i wanna say half inch. and no the ground cable is not ran all the way back from the engine block.
While it doesn't hurt, as long as you have a good connection to body from battery and from body to block it isn't necessary... Not grounding at battery and running a cable to block, then to chassis can cause voltage drop issues... Basically it's just like adding another 15+ft to the positive cable... BTW A good body ground would be something like a 1.5" brass washer braised to chassis at battery and also at point where second cable connects from block to chassis... Connect cable to washer with at least a 3/8" bolt and don't spare the dialectic grease to keep rust/corrosion away...
Scratchin my head on this one...................... Seems like you're saying two different things. Relying on a 40+ year old unibody to be a reliable ground path for the starter current just doesn't make sense to me. It's like adding way more distance than 15 ft. in my mind.
Basically unless the body is more rust than real metal, all that steel is a better conductor than probably a 1.5" cable... Key is to be able to utilize it and why I mentioned brazing a brass washer to chassis(one on each side couldn't hurt)...
Thing about the unibody now is, you've got 40 year old spot welds transferring the current, there's not a single unrestricted path for the current to follow (one piece of steel) but several pieces held together with spot welds.
Well no doubt one spot weld cannot carry anywhere near the load and many floor pans have issues after all these years, but there are well over a thousand welds... Sooo if each good one could only carry 10A and assuming 500 x 10 would equal 5000A... There would still be a good current path through the roof if nothing else... (if you hair stands on end while cranking may want to explore the integrity of your floor pans) Ever think about the '69 & '70 Boss 429 Mustang? They have trunk battery from factory with negative cable bolted directly to trunk floor and another from chassis to block... Only a full length positive cable was used... http://www.semomustang.com/store.aspx?panel=1&CategoryID=138
Yea, but there's not like a thousand welds in that path. Nor even 500. Even less thought the roof structure. (the joints at the top of the rear quarter and the even smaller joints at the bottom of the front pillars) And as I said, it's a 40+ year old body that's been subjected to "shake, rattle, rolls" and the corrosion over those 40 years. Your comparison to the Boss nine thus is moot. That was done when the cars were new. We can agree to disagree here, to me it just makes no sense to run a positive cable and not run a ground at the same time. I did and I still had problems with hot starts. And that was with all new parts. (both cables, starter and solenoid)
So you think roof, quarter panel, etc welds don't carry current same as the floor pan??? Well you need to think again, any point you connect to is the current path... Anyway if the welds were as bad as you seem to think, the car would tear it's self apart on the first good clutch dump... I'm done...
. You can have a ground through that path, but if the resistance through it is too high, it's not going to work as it should. Measuring the resistance will tell for certain. And to make sure, it should be done several times with trips around town interspersed to make sure it stays the same. But as I said, it makes little sense to to me to spend the money on mounting the battery in the trunk and short change yourself by skimping on a separate ground cable. He went whole hog with the EFI conversion, he should have gone the rest of the way here.
Man you guys are overthinking this one. First off there's thousands of 40+ year old cars with relocated batteries grounded in the rear, It's a standard practice in racing and for any one wanting to free up space. If the spot welds and metal are so bad that they can't pass current then the car is unsafe to drive.
My brother has 51 Buick, battery in trunk, grounded to floor pan.. He has a sbc and after several years of having hot start issues caused by header heat, he finally figured the 12v wire to the starter was building up resistance after everything under hood got hot. I believe he bought some kind kit from Painless Perf. to remedy the problem. Long story short -- wasn't getting enough volts/power to starter after it got hot. There are several articles on the net relating to this issue.
I know I'm reviving an older thread. But i just went and replaced my started solenoid with a new one. Took off all pos/neg cables and cleaned them. Went to start and all I heard was a loud buzzing from the solenoid. It clicked oncenter so I know it has power. But i believe my battery was drained so I have my jump box on the charger. Back to battery grounds and block grounds. I have both. Battery is grounded in the trunk. And the block is grounded under tho hood. I'll post pix in a few minutes of the grounds
