its simple logic you have to work the 4 cylinder much much harder than a v8 to get the same hp. no matter what quality the parts are you are using that will still take a beating on the reliability side. what turbo's and nitrous does is effectively make the engine work like a larger engine, its allowing more fuel and air usage which is the same thing displacement is.


who cares about mpg when talking about performance that is a cop out, any turbo engine will make decent mileage if you stay out of the boost, hell my dads diesel can get anywhere between 8 and 20+ depending on how much i stay out of the boost in a 5k+ lb truck.

my friends mk3 supra has a ls1 turbo in it, it gets in the 20's mpg wise while making 420hp and 450ft/lb to teh wheels while on a very conservative tune because he's on 89 octane at the moment....


for 7k my new engine that i am putting together is going to have around 660-690chp n/a, another grand for a wet kit and i will be pushing close to 1000hp.


more displacement in a properly built engine will always net more hp with the same power adder used...