I need schooling - old vs. new engines

66fs said
You can have performance and mpg. Been doing it since the 70's. Carbs and all. How much HP do you want or need? Any motor that sits between your fenders. Why spend the coin for a new drivetrain and cobble it into your 60's or 70's A Body? Just buy a new car.

There's a point where that doesn't work out so well, I'd say around 600 HP. At that power level you're pushing the limits of a garden-variety LA block (and need thousands in aftermarket heads, cam, intake, carbs) and to get the 25+ MPG you'd need to "cobble" in some kind of overdrive trans which you'd have to do for a G3 Hemi anyway. G3 6.4L can hit 600 HP with a big cam and CASCAR intake, no need for head work or internals. So at that point it's kind of a wash, either dump money into a max-effort pump-gas SBM or dump money into parts to swap a new Hemi. And if you go with the Hemi there's far more potential power to be had.

With that said I have a 2014 5.7L sitting in storage but the 450-hp 5.9L Magnum/LA runs so well in my Duster I currently have no reason to swap. That engine has Cometic head gaskets and head studs plus factory Magnum short blocks are known to safely handle ~15 psi of boost so when I'm ready for more power it's simply a matter of bolting on a Procharger. On the topic of carbs as well, the engine currently runs fantastic with the 750 cfm Street Demon but when I'm playing with boost I'm gonna want EFI and electronic timing control. Yeah blow-through carb would work but I want that closed-loop AFR management too where I don't need to change jets when the weather or altitude changes.

I'd buy a modern Hemi car if they didn't all weigh as much as an old C-body or more. Just going off wheelbase and weight that's basically what a modern Challenger is, a 2-door C-body with 12" taken out of the wheelbase. They're friggin yuge and it really bums me out. I watched a video of a guy on YouTube who swapped a stock 6.4L SRT Hemi into a Duster with a T-56, since it's about 800 lbs lighter than a modern Challenger that car is as fast as a stock Hellcat with 200 less HP naturally aspirated and reliability of a factory-stock engine.