Small displacement engines such as the LFX ( 3.6L=220 in^3 ) need to be turning more RPMs to make high HP. For the LS4 (5.3L=325 in^3) , because it has more torque, it makes good horsepower at lower RPMs, and hence accelerates well from a standing stop.While it's the same HP, the LFX has a lot less torque - so even though the SS is heavier and the same HP, an SS will still "outrun" a LFX Impala.
Don't get me wrong, I love the LFX in my 2012 Impala - but the SS will still win in a race.
Having driven both, but not raced them, my take is that the SS will definitely get the hole shot, and maybe take the ⅛ mile, but the LFX will win the quarter.I remember having this "debate" here on the forum before - and someone had both an SS and an LFX Impala and they said that the SS beat the LFX Impala every time (I think he was racing his wife, if I remember correctly). He made it sound like it wasn't even close really...
Persoanlly, I've never driven an SS, so I can't speak from experience. Just from what I've read.