Question: How accurate do we need to be with setting TDC with computer control engine management? Is the thumb over the #1 spark plug hole method acceptable to get it in the "ball park" or does the motor have to be at the true TDC to function properly?

 

You can be off and the engine will still fire up. If to far advanced the engine will lug when cranked.

 

So let's say you set the base timing at 6* but it's actually at 5*. Your at crank spark advance is going to be less than what the ecm commands by one degree. It really won't matter at all on a batch fire setup if you're off by one degree as far as injector timing goes. The base timing parameter just tells the ecm what the base timing SHOULD be. If the base timing is set accurately, the commanded spark advance will match the at crank advance. There are some caveats, like the module latency. That needs to be correct, or the commanded advance will never match the at crank advance.

 

So would there be any advantages to setting it to true top dead center? , say using a piston block?

 

You can always use a piston stop to accurately locate TDC, but that's not where you'd want the timing set to.

The ECM does not know nor care what the static mechanical timing is set to. All it does is put out the spark signal some length of time after the last reference pulse it received from the dist. IOW, if the stock spec is 6 degrees static, and the ECM's program says to add 20 degrees for whatever conditions it's under (load, RPM, etc.), and you set it to 6, the it will end up at 26; if you set it to 10, it'll end up at 30; if you set it to 15 it'll be at 35; and so forth. Engines almost never run their best at the stock spec, not least because the spec is designed for emissions compliance, not best running.