383 vs 400

2011 thread revived in 2017 and again today.

400 is a MUCH underappreciated Mopar engine.

The biggest disadvantage is lack of off the shelf pistons for anything but a stock compression ratio.

Note on page one a common book HP number mismatch was given-

383 with 330/335 HP and 400 with "only" 250.
That is a gross vs net mismatch and is an incorrect comparison.
I'd bet dollars that on a dyno, the numbers would be MUCH closer.

Also most stock 383 cars in the 60's had a standard 2.94 or 3.23 (maybe even 3.55) rear gear.
OTOH most late 70's 400 cars had a 2.76 or even a 2.4x gear.
That's another unfair comparison.

I've had both and found them to be very, very similar.
(383/906head HP, and 400/452 head in the same B body car with 3.55 gears)

A point I didn't see but may have missed is the early non-HP 383 came with smaller valve 516 heads.
Almost all 400s came with 452 heads which are very similar and flow like the "HP" 906 head from the 60's.