I bought a new 55 Cheve with the V8 engine and the plugs only lasted 1000 to 1500 miles no matter what brand or heat I tried. The insulator glaze was burned so cleaning did not help. The dealer suggested I put in a dual-point distributor but that made no difference. I traded the car in on a new 57 Cheve with the 6 cylinder engine and plug life was short on that engine also until a new plug called “power tip” was introduced and then the plug life was about 5000 miles.