[serialk11r]

Aside from the substantial cost of batteries and controller, there is one more annoying hurdle which is actually getting power to the crankshaft. Every single combined alternator-starter system out there uses dual belt tensioners, and I think there's a good reason for that.

You would have to figure out a place to add a second tensioner to your belt before the motor if you want to replace the alternator with a motor. Or, you can use a toothed belt and add an extra pulley. I know that's a common way to power dry sump systems, but I am not sure how difficult it would be to do that.

There is of course a limitation, which is that the belt cannot handle very much power. Supercharged engines are probably the most demanding on the belt so that's a good place to look for clues as to how much. I recall doing the calculations and a Lotus Elise SC should put something like 10Nm on the crank pulley, which is probably around 20Nm on the supercharger pulley. Since the supercharger pulley is fairly small, I think with a larger pulley you could probably send 20Nm to the crank safely with a 5" crank pulley but I wouldn't go above that. Your engine pulley is I think 7.25" so you might be able to get away with close to 30Nm.

Frankly for your application I think this is the wrong solution; you already have a big V8 with a lot of power ready to go, if you press the gas pedal harder and it turns on the extra 4 cylinders, what is wrong with that? The efficiency of your engine actually goes up because those 4 pistons aren't dead weight anymore. The point of a mild hybrid is to provide some extra torque and stop start capabilities, but your engine is already very powerful and has quite a bit of fuel saving measures, so it would need a very powerful electric motor and battery to make a difference.