If it has the same muffler mounting dimensions as the .46 FX then the Tower muffler will fit. I use it on my .52 size and it gives a good 5-800 rpm more than the stock muffler. As others have mentioned, your plane is very hevy for some reason. An Lt 40 should be around 6-6.5 pounds and that is your biggest problem. I`m not so sure that you will be happy even if you get the Tower muffler, you need a lighter plane or a bigger engine. A friend of mine had a FX .61 in his LT 40 and with APC 12.25-3.75 he took off on about 10 feet and went vertical, his plane weighed a little over 6 pounds