The only thing that sounds like a Merlin is a Merlin unfortunatly.
Trying to emulate the sound of a simple Cessna light aeroplane is difficult enough if not impossible with a model.... our engines rev to high and the prop (the biggest contributor to full sized sound) are so small in comparision.

We experimented with a 3rd scale Tiger Moth/G38 with a Tony Clark reduction drive and super mufler togerther with a 36" wooden prop (max revs about 2200rpm idle 500rpm). Without doubt the most convincing combo I've ever witnessed. I have also seen two different aeroplanes powered by the wonderful Moki (RCS in the USA) 215cc radial. Both were seriously large models swinging big wood... now I'm quite sure a real FW. 190 would sound distinctly different but once again, boy this was an impressive sounding RC aeroplane... Once you get this many cc's poppin' and coughin' and again a seriously large prop beating the air, things start happening. You get the Doppler effect, you get the prop sound... it's not "scale" but it's starting to sound like an aeroplane and not a model.

Unfortunatley, you just can't "fake it".