Custom Built Limited Slip Differentials. These units are custom built and are available in a variety of different ratios ranging from a 3.46, 3.64, 3.73 to 3.91. We typically stock the most popular 3.73 ratio and the other units will be custom built. Please allow 4 weeks for a custom gear ratio. There will be a refund of $300 for a useable core when we receive it customer responsible for return shipping. Total of $2,295 after core charge is returned.