Every plane is different, like they said. Really no set formula. I just ordered a SV26 that has a rear carb and pitts muffler for a Carl Goldberg Ultmate. I picked it up with only a few flights on it. The guy had a Magnum .65 on it and had to add nose weight. Total for engine, muffler, mount, and weight was 2 pounds and 6.6 ounces! The SV26 will add a pound of weight. I'll be able to use a little bit smaller fuel tank also to save weight. The plane with the glow engine weighed 8 pounds 3 ounces, with a wing loading of 19.03oz. With the 26 the weight will be 9 pounds and 3 ounces and the wing loading with be about 21.5oz. Pretty good for a biplane. Nothing will stick out the side of the cowl. Engine will hang out of the bottom though. That's OK by me, it'll be nice'n cool.[sm=shades_smile.gif]