These are the current Davis In Cowl mufflers, they are of high quality, very quiet and do not effect rpm. The engines are an MDS 2.18, Irvine 1.50 and a Dieselized Irvine .25, the extra muffler goes on a Super Tigre .90 also Dieselized. You'll just have to excuse the clutter on my work bench, I'm suffering from a real bad case of projectitis and have been going through engines checking bearings, re-building an engine for a friend, you know how it goes.