I have not found one made for models. I have made one that worked great for larger model aircraft engines. I just welded a plate to a .625" shaft 18" long, then mounted that into a pair of cheap ball bearing pillow blocks. I clamped an arm to the shaft that attached to a scale. And then used a tachometer and a calculator for determining HP. It was not calibrated for accurate HP numbers but was excellent for making comparisons.