I have both the RCV60SP and the RCV91CD, both are working flawlessly and they tend to get stronger with time. I due like to stress that the break in period is very, very important. Not only that but also make sure they have plenty of cooling. Follow the recommended props as well!!!! Once you achieved these goals they should not give any problems. I'm planning on getting the VQ FW190 once they are released and I'm planning on getting another RCV SP series engine for the FW190. Customer service is also WORLD CLASS!!! O yeah.....almost forgot, the sounds of these engines are incredible!!!!