In this paper, a rate allocation policy is proposed for truncated transmission of spinal codes based on imperfect feedback over block fading channels. By constructing and solving the throughput optimization problem, the optimized rate allocation policy is obtained under the constraint of limited transmission attempts and frame error probability. Both analysis and simulations show that the rate-allocated transmission of spinal codes achieves higher throughput in block-fading channel with noisy feedback compared to the fixed rate transmission.