OK, you sparked my intrest. I have built two GP RV-4 kits [ one modified to RV-8 specifications. ] Both powered with very reliable SuperTigres. One a .51 the other with a .60. The .51 is a little underpowered, the .61 works out much better. Both side-mounted using a Pitt's style muffler from Tower hobbies. The planes are ok[&o], I'm not too excited, and I use them once in a while. MM