Gains to wheels? I'm betting 2 maybe 3 hp up top, but with a loss or torque due to inertial difference.
Changing the mass of the flywheel will change the feel of the engine's revability, but when you're balls deep in the throttle, having a sprung 40lb flywheel, or an unsprung 25lb flywheel won't make a huge difference in overall power output at the tires, especially considering there's still a 30 pound clutch assembly attached to it.
2013 Focus SE 5M Daily Driver
2003 Mustang GT V8/Auto Wife's Daily
1986 Mustang GT V8/5M Toy
- Jody -