I believe you will need to add about 15oz of lead in the tail for the hellcat to balance. They quote the Zenoah will weigh 41 oz compared to 19oz for the Saito 100. I will use the Saito 100 like I have used in all my Hanga 9 warbirds. No additional weight required. With the correct exhaust system, I get very little residue on my aircraft when finished flying.