This engine is one of the strongest they made, so it was used to be driven for lots of kilometers and not complain. That's the very good point of this engine by the way. It is indestructible, doesn't need a lot of attention, and is very easy to repair. Plus it's very cheap to maintain. So don't see the glass as half-empty, see it as half-full.

So if you want a 309 with more power, the only solution would be to buy another 309.