How much is a lot?
I am talking about 164-165 degree ( it's 5.0 mm exhaust height). There is no way you can go higher due to the limited pipe space.
It is not about exhaust duration-it is whole chain of events happened in our two cycle engines. If you just increase exst ( I never try this thing-doesn't make any sence) defenetly yu will loose torq and milage will go down, but if everything else will be broght to specs-you will gain 1 minut easy. On Novas based engines with modded timing 6 mnuts 30 second is absolutly normal run time, but if material for P/S set are changed ( AAC and BRB) you can lean much further with a lot of gaining run time and power.I am talking about use fuel as fuel, not as cooling liquid. It is totaly from my knowlodge and my expirience and it is not meaning this is ruls. So if you want to prove it your self, you need to try. But please remember-if you change one thing in chain, you will need to change everything else. If everything dne right-milage will be realy good.