Quite a few differences. The short block is essentially the same, but that's about it. The 525 has alum. Edelbrock heads and the 500 has cast iron. The camshafts are different. The 500 has Etop headers and the 525 uses the sweeper style Sport Tubes. The 525 is close cooled. The 500 uses a Mefi 3 ecm, where as the 525 has a Motorola 555 controller. If you install the Whipple on a 525, you need to remove the 555 and install the Mefi 4 ecm and harness that comes with the kit. You also have to install a distributor, coil and plug wires, since the 525 is a DIS (distributorless ignition system). The 500 already has a distributor, coil, etc. That is the biggest reason that the 525 Whipple kit is so much more than other kits. You have to add the ecm, harness, dist., coil, plug wires, sensors, etc. That all adds a couple grand to the kit. It is still worth every penny.