A buddy and I both have TwinStars with GMS .32s. We had trouble running 9-6 props or any other that let the rpm go up. I think it may be a sympathetic vibration problem and fuel foaming, but I can't be sure. Our problems went away when we went to 10-6 props and got the rpm down. The 10-6 Master Airscrews run fine. With 9-6 APCs we landed single engine about half the time.