Yeah, true the RX-8 has 175bhp/l and the tuned ones (like the RX-7 RZ) have almost 230Bhp/l
But the fact is they're rotary engined cars therefore they don't really count. I think
Dev_zero was implying the traditioanl piston-engined sense.
I think Skylines like the R34 GT-R V-spec 2 have about 130hp/l (even though they're only supposed to have 105)
But furthermore, what about the old style F1 cars? A world of their own i know, but some of those managed a whopping 520hp/l! That's a power to displacement ratio!!