ok, well, there are basically two different ways to do a hybrid vehicle:
(1) the way the US Navy used to do submarines before nuclear power: both the diesel engine and the electric motor are on the drivetrain, and you can switch between them. While submerged, the electric motor runs the boat, but while on surface, it is diesel. In the case of cars, the electric motor drives the car below a certain speed, then the gasoline engine kicks in.
(2) the other way is that the engine is NOT on the drivetrain, and it is only the electric motor driving the vehicle, and the engine is used ONLY to provide electricity. Batteries are used primarily, if there is too much electrical demand and/or the batteries run out, the engine starts, and any electricity it provides which is not used for the motor is used to charge the batteries.
So in case (1), a V8 could still get an advantage, since it is on the mechanical drivetrain. In case of (2), you can theoretically get by with a leafblower engine, as long as it generates enough electricity to power the electric motor. In the case of (2) the engine always runs at the same speed whenever it is on, in the case of (1) you can have a variable speed engine. Actually, in both cases the V8 can be an advantage to some extent, as it could drive the alternator (or whatever) a lot faster.
Plus, there is no reason "550 horsepower" cannot refer to an electric motor. Horsepower is just the old British unit (now, mainly American unit, as we are the only country left that mainly uses that system) for what is known in metric/Systeme Internationale (SI) as Watts. 550 HP would be 410 kW.
http://www.onlineconversion.com/power.htm
And yes, if it is a "hybrid" there is an electric motor involved in the process. So in other words,
a hybrid vehicle is in fact an electric car, just with an additional source of electricity for the motor other than the batteries. In fact, with the Toyota Prius, there is a plugin hybrid mode, where you can charge the car at home and run on batteries even longer (and the car can be modded to have more batteries). This mode is factory installed only in Japan, but the car can be modded to enable it on US models.
btw on a modern nuclear submarine, we can still run on batteries in the event of failure of both the reactor and the diesel, but it would be very s-l-o-w. Our top speeds are classified, so I can't tell you exactly how slow, but obviously it would be very slow. We can also turn the rudder in complete manual mode, that is to say, you can get buffed guys in the Engine Room and turn the thing manually. If the boat is that broken, though, I doubt operating the rudder would be the biggest problem...
--Brian ("Qualified in Submarines" on the USS Florida and USS Asheville)