Good day, my first comment is how much power do you need?? How many amps total, not just at idle. The 2500 series and 4000 series turn on at fairly low speeds. But this can also be manipulated by changing pulley ratios too. Look at our website where you can see performance curves of our alternators. If I knew how much power you need I can make a better recommendation. We also have marine rated alternators too if that is important to you, email me or try calling our tech service line at 866-288-9853. Thanks