How different / how important is back-preassure to how well a gas engine runs Vs a nitro ?
I have a muffler for a dle30 that has some leaks in it due to a modification to the shape of it. how airtight (aside from the exit ports) should a gas engine muffler be ?
I recall my muffler coming off of my lawnmower and it still ran- just really loud. - This may be very different (or not)- but how -also will it affect performance ?

FYI- I asked this question before, but never got a response: So I'm hoping if I phrase it differently, I might get some guidance.

Back pressure may help a slower idle speed but it doesn't help high speed

Usually backpressure might help with idling, but not much else. Now sometimes there can be some subtlities where a engine needs just a little bit of backpressure to run better where it might be more tractable with a little backpressure.

The glow engines use muffler pressure or back pressure to pressurize the fuel tank so the engine can draw fuel more easily. But with gas engines, if you are using a fuel pump/regulator system, then you don't need muffler pressure of course.

Yeah the muffler could leak a little here and there, it depends on the person as to whether it is too much or not.

The 2 stroke engines we use as modelers do not require back pressure to perform properly . most but not all actually perform best with no muffler or backpressure . The problem of a muffler not sealing is that it usually changes the tune slightly when it comes loose and may change idle or transition quality from what is was before it developed the leak . The change in performance is from the change in backpressure after the engine was tuned not that the engine needs or doesn't need back pressure just that the conditions have change since it was tuned.

Thanks CK1 & earlwb !
I really appreciate the Insight