do they work well on big inch builds say like a 117 twincam or is it minimal performance gains .
Stepped pipes lift both ends of the curve, and help fight reversion.
If you really want to do it right, have Burns stainless design the pipe to match your engines build specs.
https://burnsstainless.com/
True duals to a good stepped 2-1 will see a major performance improvement (especially if the cam has lots of overlap)