Funny, I have never driven a big block that could be considered a "turd" and I've driven all kinds. Supercharged ramjet 502, to a bottom feeder smog era 454. Even a 8.1 burb.
No healthy (proper compression, firing on all 8, fuel and spark, etc,) BBC is a turd. Even a smog era BBC is still a one wheel tire fryer.
And yes I have driven all kinds of modern diesels. I would regularly race and beat my uncles 12v with my tbi big-block.
Was it modded? No, but either is my tbi454.
I understand turning up the pump and turbo and blah, blah, blah, I can put cam and heads on a big block. So I won't compare modded stuff. Stock via stock.
Fuel milage, you say? The extra cost up front and the cost at the pump. I can feed alot of fuel in a BBC for that extra cost. So yes, they eat fuel like a fat girl on hot day eating popsicles.
Maybe it was a the crew dually weight. But turd? I doubt it.