Has anyone attempted to engineer an exhaust that, like a two stroke dirt bike, has a baffle designed to push a pulse of fuel enriched gas back in to the engine to improve power/economy?

 

Well... Kind of an answer to my own question, I suppose exhaust overlap creates this effect on it's own. And of course the problem with that is reduced intake charge efficiency... That being true, why exacerbate the issue by designing and exhaust that sends pulses back in to the engine...

 

Along these lines Mazda did...sort of, build an expansion chamber into the design of the JDM down pipe.
At least it reminds me of the exhausts on all the small dirt bikes when I was a kid.