1970 Datsun 521 L-16 engine with rebuilt "210" head.

Blue test is with the engine driven fan, points distributor timing set @ idle 5 btdc
Red test with fan removed.
Green test Electronic 1980 Nissan 720 (200 SX) distributor timing set @ idle 12 btdc
Purple test same as green but NGK Irudium BPR5EIX-11 (-11 = .044" gap)