Eight tanks so far. This is one of the best little engines I own. I have three! I will switch to a 6.5 X 6.5 APC next. Then a 7 X 7 Graupner. The Graupner is an electric prop, but works just fine on our OS .15 LA's we use for club 20 racing. The LA turns 16,400 on the 6.5 X 6.5. This little MDS is great engine. You will love it!!!