When it comes to building a high horsepower engine, you can’t beat the Ford 4.6L block as a base. The stock Mustang GT block has been known to handle up to 500 flywheel horsepower. However, this is flirting with disaster. Granted, with the proper mods the 4.6L can handle well over 1000 rwhp! Not bad for a stock cast block, especially one with the revving capability of the 4.6L.

There were two cast iron blocks used in the Mustang GTs. One is the Romeo, and the other a Windsor (named for the factory they were produced at). The Windsor is pretty easy to identify as it has a “W” cast into the valley area between the cylinders and also on the front of the block. The Romeo block has an "R" stamp instead. Instead of taking apart your engine to find our which engine you have, you can also reference the VIN numbers. The Windsor block has an "X" in the 8th spot, whereas the Romeo has a "W". The Windsor The main bearings on these two blocks are not interchangeable. These blocks utilize two main bolts and two precision dowels to locate the main cap.

Keep in mind the Romeo block found in the 99-04 Mustangs is the same as the one in the 1996-1998 Mustangs.