That is not a "primary" ground. Far from it. There is a huge ground wire bolted to the starter motor that goes straight to the battery negative post. That is the primary ground from the engine.

Given that this cable happily carries ~100A during cranking, if the cable is in good condition and it's connections are clean and secure you have to question the worth of adding extra grounds from the engine. The current this wire carries while the engine is running is far less than when cranking.

That clip on wire is the primary ground for the body (including the ECU)..

Yes NZ, but you have to envision the current flow paths here (or more accurately, the bonding). I, like others, figure the very best spot for that ground is right on top of the starter. That's the component that uses the most "juice", therefore that's where the juice terminal needs to be. Our metal-to-metal contact points on our engines (starter-to-tranny, tranny-to-rear housing, rear housing to rotor housing, etc...) leave something to be desired when considering electrical flow paths. Especially mine now, with hylomar "squished" between them, lol. Do you really want 100A flowing through your rear housing-to-tranny-to-starter mating surfaces?

This is the very reason I installed a stout (10 gauge) bonding jumper right on top of that rear rotor housing ground, directly to the firewall. Now that my starter is directly fed, and that housing ground is directly fed, there is no need for any worries about the conductivity of the housing-to-housing (or tranny-to-starter) contact points. Now, I don't call this an "extra" ground, it is nothing more than a bonding wire, but I guarantee it provides a better electrical path to the chassis "potential" than the OEM setup. SureShot, you may want to try this...You're right, that firewall "spade clip" is cheesy...

Thanks, RETed, exactly the info I was looking for. I reiterate my demands for editing that "grounding how-to" thread so these guys will quit grounding that boost sensor and then wondering why their cars are running like crap... :)

Any links to a comprehensive write-up on relocating the battery on the FC?...thanks

That's basically what I have (except I used two 8GA wires) plus one from the battery negative terminal to a leading coil mounting bolt. I figure any more than that is just silly overkill.