Does anyone know if 65-66 HiPo flywheels, casting# C3OE-6380-B, were cast differently than standard flywheels? I've been doing some research on these and think they might have been but can't find any info anywhere to support or reject this. Some of the books out there say the C3OE-6380-B is HiPo specific but that's not true, I've seen plenty of them that were original on standard 289's as well. I did find out that the HiPo ones are counter balanced differently, 30.4 oz.in. compared to 26.2 oz.in. for the standard flywheel. Apparently the difference in balance is to compensate for the crankshaft counter weight (hatchet) that the Hipo uses on the front of the crankshaft. Ford did mark the HiPo units with an orange paint daub. What makes me think HiPo C3OE's may have been cast differently (like HiPo cranks) is all the confirmed originals I've seen also have a polished area and hardness test mark which I've never seen on a standard C3OE flywheel. The attached pics of the original flywheel from my 66 GT350 show what I mean. If this isn't a hardness test mark what is it? If it is, why would they test them if HiPo flywheels weren't cast differently than standard ones? Any thoughts? Thanks, Dave
