Vintage Cars: SD 455, duty engines, original tune

Question
Was the Super Duty motor a detuned race engine?  I read somewhere that it was a detuned nascar 366 engine and could be converted with a cam intake and headers back to its original tune.

Answer
The original "Super Duty" engines were intended for race duty starting in 1960 with performance parts on the 389.  Then things got real interesting in late 1961 with the 421.

But NO, I don't think the 455 was ever a 366? that was detuned for street use.  Never heard anything about that, just one of those things that probably got started from incorrect information.

The original 421's were run just like that, they ran whatever the manufacturer had till the late 60's I think.  Not exactly sure when they went to mandated cubic inches in NASCAR, but today, the engines in NASCAR have NO relationship in effect with any factory engine.  They all started out that way, but today they are specific castings and heads and I don't think there is anything inside that is very similar to any street engine except maybe the original bore spacing etc.

Don