here you have some reading about exhaust gases and some possible use (not only for aviation)
http://www.formula1-dictionary.net/coanda_effect.html
https://en.wikipedia.org/wiki/Coand%C4%83_effect
I’ve just watched a video about the Rolls Royce Merlin engine from WW2 and they got the equivalent of 150HP extra thrust by pointing the exhausts backwards!
I don’t think that is ‘thrust’ from the exhausts per se, rather the positive effect on gas flow through the cylinder heads of having the exhaust stacks exit into an air flow that’s going in the right direction and thus adding a suction effect rather than (if you point them forwards) the exhaust gases having to push against a 300mph+ airflow trying to push them back into the engine!
Active exhaust scavenging, I think the motor racing lot call it. The numbers sound sensible, as in automotive tuning you can easily put 10% on peak power by optimising an exhaust system for performance when compared to a compromise system that is mainly concerned with noise reduction as well as cost and ease of engineering.
