ah, how you should really ask this question on ClubSi.com's Si vs. All forum...
answers:
1. Z06 has an LS6 350cid motor, 5.7 liters, not 7. This is now at 71hp/liter
2. japan car manufacturers get taxed based on displacement. This is why so many cars are 2 liter or under turbo vehicles, or extremely well engineered car that make crazy power but no torque.
3. "if honda made a 6 liter v8, it would make 600hp blah blah". No, this is not true, because if honda did make a v8 making 600hp, it would cost an arm, leg, and a testicle. This is why honda does not produce big engines. Biggest engine they make is a 3.5 liter v6, and most powerful is the 3.2 liter v6 in the NSX
4. State of the art? vtec? Ford had variable valve timing back in the 40s. DOHC design? Back in the 20s used in racing. I have a rotary rocket magazine I got from RacerX from 1982 that has an article of a prototype mazda hatchback, awd, WITH variable valve timing, 1.3 liter dohc 16 valve turbo motor. Just because it has high compression it doesn't mean it'll make crazy power. It just means you have to fill up with 91 octane instead of 87.
FWIW, my '99 neon r/t is 2 liter, 150hp dohc, 3.94 gearing, and runs as fast as a 160hp civic si. And gets better fuel economy. And has no resale value
5. LS1/6 engines are underrated, and undertuned. This is the same reason turbo vehicles from factory make low boost. We all know the L28et can do 10psi without changing anything but adding an intercooler and a manual boost controller and making 60 more hp. My friend's 01 z28 camaro made 440 hp to the wheels with an ls6 hotcam package, and some other tweaks. Naturally aspirated. You won't see a honda making that much power on a b16a2 block.
6. While we're at it, let's bust another myth. The chevy smallblock, ranging from the old 4 bolt main 350 from '50s to the all aluminum ls1/2/6 blocks of today, are all (with exception of the LT5, that was a DOHC 32 valve motor) over head valve design with pushrods. Honda crowd always refers to pushrod motors as DINOSAUR motors... When in fact pushrods were introduced some 30 years after overhead cam design was created. Pushrods are simpler design, less moving parts
7. In short, hp/liter arguement is good for people who like to punch numbers into a calculator and masturbate to the end result.