YES- the muffler will make a considerable change in power
Guessing?
No- - a few year back i tested most of the ZDZ engines coming into the USA- ( for the folks who imported em) as well as Evolutions DA's and also made up ignition conversions on ST2300 engines .
Opinions are opinions and everyone has one.
The short story is that on ANY gasoline engine, the exhaust system plays animportant role .
Pipes ALWAYS produce more torque- which results in more rpm - there is NO max torque rating which means anything unless the exhaust system used is factored in.
do emwrong tho and you loose power .
The in cowl small thingys are typically the worst power robbers .
Why?
in a nutshell -theses designs are simply air pumps - and respond just like a table fan.
restrict output and input decreases. No exceptions
The free flowing exhausts empty the chamber quicker (faster flow) which allows the crankcase to pull in more and flow into th e chamber faster - filling it more completely - no exceptions.
A correctly setup pipe , extracts the spent charge faster, earlier , again creating a strong extraction from the crankcase into the chamber - it also stops spillage of fresh gasses out the exhaust -resulting in MORE fresh fuel charge ( density is higher ) and the result is of course - more power .
There are lots of goofy explanations about pipes but the bottom line is - they simply provide for a stronger faster filling of the chamber - period.
Oh yeh -they don't push burnt gasses back into the chamber.
If your model simply does not allow for a full pipe - there are a few (very few ) decent mini exhausts which are not bad - typically tho you need a long header to make any of em work
IF you simply must have the muffler in the cowl- make the muffler as large as possible with a smallish outlet - this is the most effetive setup for least power loss with most noise reduction.
IF you need more power with your ignition engine - switch to alky and 5% nitro and 20-1 synthetic (compatible type) oil.
Now you can use a carb with double the flow and power goes WAAAAY up so does fuel consumption. No exceptions.
I did this with the 2300 Tigres and power, starting etc., was excellent - I did use more oil -of course - 20%
The best of the small engines I tested and used were the 26 Evolutions on a full pipe - best design. on 18x6 props we turned these 8800 on the ground and 10,000 in the air (internal ignition tach)
This new engine should be great for smaller designs whre optimal power per pound is not required -