Back when people were starting to become aware of the stroked B motors, it took quite a bit of time (time = money) to cut down the RB crank mains to B size. So, the typical thoughts of "Why not just start with a RB motor to start with?" Like building a Chevy small block, just head to a 350 to start with.
NOW we have made-to-size cranks/rotating assys that make everything a bolt-in situation. The somewhat unfortunate result is that now we have (as chronicled by an episode of "Nick's Garage" graphically pointed out), a LA408 can make 425 well-mannered horsepower, so that suddenly gives those discarded motors a reason to live, if that's what the car came with. As stroker 440s go well past 530cid in the process.
With the advent of 6-8 speed automatic transmissions with low gears in the 4.6:1 area, low end torque seems to be less important as the engine gets through those lower rpm ranges quicker as a result. The magic of EFI then allows them to use 3.23 rear axle ratios and cruise in OD with a .70 ratio, too.
The magic of the LA340/360/408, like its similar Chevy 383 SBC/302/350/327 competition seems to be related to their approx 4.0" bore diameter. Reason? It's been there for years, just that in more recent times, due to emissions research. It's the time it takes for the flame front to travel from the spark plug to the opposite side of the combustion chamber. And to it efficiently and expeditiously in the allotted time it has to do it in. Of which the "fine wire" electrode spark plugs play a vital role. Which also means a closed chamber cyl head can be better than an open chamber, with respect to "active air flow" due to "quench" turbulence. LOTS of side issues!
Back in about 1969, Chevy built a CanAm430 big block motor. It ran better than their existing 427 (truck-based, factory race motor). The reputed reason was its "optimal" bore/stroke and rod length/stroke ratio . . . which were the same as their SBC302 motor. AND . . . the same as the Chrysler 383! Bore/stroke was (IIRC) 1.27 and RL/S was 1.9, with lower RL/S being more "torque oriented" and higher meant better high rpm performance. The Olds 350 was just a hair over 2.0. Lower "rod ratios" also influence how much side-loading the piston skirt sees against the cyl wall.
In the middle 1950s, as mentioned in an article on Chrysler engine design in an issue of the old "MoPerformance" magazine, Chrysler's "take" on rod ratios related to the skirt/cyl wall loadings. Chrysler determined that a 15 degree swing of the connecting rod on the piston pin was "the limit" for best power and reduced friction. In THAT criteria, the 3.75" RB stroke was the max stroke length. So with the existing connecting rod length, it all worked well.
One of the other reasons I liked 383s from my earlier times was a comment allegedly made by a Chrysler operative at a press showing of the new 1965 cars. That the 383 2bbl was a favorite among Chrysler engineers (for their personal/company cars) for its balance of power and fuel economy. Then, as now, I prefer relaxed cruising at 90mph with the engine at the peak of its rated torque curve over how fast it might get there in normal driving. Usually getting 15mpg doing it. Yep, it'd still cause some tire slippage from a dead stop on pavement, too. All good!
I know people like their RB stroker motors, but a ZF 8-speed behind a nice 383 might surprise people. Add some modern combustion chamber alloy cyl heads and such, even more so.
Happy Holidays!
CBODY67