SD 455 cars off the showroom floor would run mid-13s which was quite respectable at the time for a low-compression smog engine.
My daily driver low-compression D-port 455 with untouched ports and HO exhaust manifolds easily ran high-13s with a TH400 and a 2.56 geared open rear end. SD cars had either 3.42 or 3.08 gears if I’m not mistaken, and a posi differential standard like all Trans Ams.
https://forums.maxperformanceinc.com...22&postcount=4
Getting SD-like performance out of a D-port 455 is like falling off a log.