If you're going to swap gears, the stock Traction-Lok has to come out anyway, so it's a good time to consider swapping in a performance differential. To get the most performance from your ride, you need all the power applied to the pavement. Drag cars can simply connect both axles with a spool, but a street car like PVT needs torque biasing for all-around use. I opted for the Torsen T-2 diff (PN M-4204-T31; MSRP $589) from Ford Racing Performance Parts, which uses helical gears to constantly bias torque between the two rear axles. The Torsen is quiet enough for the street and durable enough for the FR500 race cars (in T2R form), so it's a good match for PVT.