The difference is in the efficiency of the Magnum over the LA. It's a roller motor with closed chamber heads. Either one can be made into a firebreather, IMO pound for pound the Magnum is superior, especially as delivered.
The closed chamber isn't as good as the open chamber. A hydraulic roller is worthless any a performance oriented build, unless you use solid rollers on it.
So the magnum is at best, not as good as the LA because the rocker system is garbage.
