Q about starter heat shields

[5.0 Fiend]

The car is an 84, so I imagine thr starter is that old, also I am running shorty headers.
What do you guys mean by timing? Ignition? Cam? I dont have a timing light, should probably get one, I just take the number one plug out, jump the starter solenoid to get the cylinder on the compression stroke to top dead center, then I point the rotor to that wire and do a quarter mile run (estimated), and keep adjusting the dist. till I am happy with the results. Why would the timing affect the engine when hot, but not cold? The next time it happens, should I try to retard the dist timing a little bit? I guess I'll try a heat shield to see If I can pull a little more life out of the starter.