[oil pan 4]

I have a 30hp 922cc 2 cylinder 3,600rpm engine generator that needs a new exhaust system.
Because the OE exhaust system sucks. The muffler is right next to the generator and the tail pipe discharges horizontally at ground level.
I see 5 problem's with this:
1 It exposes people to carbon monoxide.
2 It kicks up dust which will be sucked up by the generator, engine and people.
3 Anything next to the tail pipe will be burnt up.
4 Exhaust heat from the muffler effecting the generator.
5 Noise blasted out the end of the tail pipe.

My solution, fire the exhaust straight up.
The carbon monoxide, tail pipe scorch, muffler to generator heat and dust problems all eliminated.

I have room to make the exhaust pipe primary tubes anywhere from 18 inches long to up to about 5 to 6 feet long max. Then put both primary tubes into a full size car muffler to tame the noise level a little bit more.

I'm going to run this engine hard, if it's not making at least 5 or 6kw then it should be off.
Normal operation could be an inrush of 20,000+VA running with 10,000 to 15,000VA.
So the tube design should be maximized for making full power at 3,600rpm.
Plus more heat that can be rejected by the exhaust the better since these engines tend to run too hot anyways, frying their oil.

What size tube and lengths should I be considering?