Does anyone know if this flywheel is steel or nodular iron?
GM part # 3991469 Flywheel
Outside diameter is 14" for years 1955-85. Crank Flange bolt pattern: 3.58"; clutch dia.: 10.4", 11"; starter ring gear teeth: 168. For two-piece crank seal. This 14" diameter manual transmission flywheel accepts an 11" diameter heavy-duty clutch. It can be used with all internally balanced Chevy big-block V8 engines.

Thanks - Tski

About 20 years ago when I was in in my first life as a hot rodder, I remember that the nodular iron flywheels had an "N" after the casting number. Not to say yours isn't...

Remember, the casting number is different on flywheels than the part number. I have also seen NF after the casting number. I think it means Non Ferrous (cast iron)??

according to the GMPP catalog, it is cast iron. if it was a lightweight nodular flywheel, it would be mentioned in the description- like part #14085720-12 3/4" OD, 1955-85,3.85 flange pattern,10.4" clutch diameter,153 tooth ring gear "Lightweight nodular iron flywheel. Weighs approximately 15pounds. for two piece crank seal".

Thanks