Underdrive pulleys are next. Again, the market has stabilized on sane underdrive percentages, so there is little chance you'll fall prey to the "race-only" mentality when it comes to pulleys. The alternator still needs to produce juice at low rpm, and the water pump still needs to turn at stoplights, and after years of over-slowing 5.0 engine accessories, the industry has found a good balance with the street 4.6 market.
One option the 4.6 pulley buyer will face is the type of pulley to use on the harmonic balancer. Because the 4.6 engine integrates the crank pulley with the harmonic damper into a single piece, you either replace the entire balancer/pulley unit, or fit a piggy-back pulley over the existing pulley. Our tuners recommended the one-piece damper/pulley replacement method as the installation is the same (you have to pull the harmonic damper in either case), and the replacement style keeps the harmonic balancer in the stock location on the crank snout. The slip-on pulley moves the balancer forward on the crank, which doesn't seem beneficial to the crankshaft, and can foul the transmission oil-cooler lines on automatic GTs. Popular brands in the pulley arena are ASP and Steeda, as well as pulley perennial March.
Another major pulley consideration is if you plan on supercharging your 4.6 at a later date. All supercharger kits-roots, screw, and centrifugal-are designed to work with stock crankshaft and accessory pulleys. So, if you buy underdrive pulleys now, then a supercharger a year from now, you'll find yourself needing to reinstall your stock pulleys. And you did keep your stock parts, didn't you?
Advice from the vendors and tuners was to simply stick with stock pulleys if you plan to supercharge at some date. Inevitably, it saves time and money.
While on the subject of supercharging, there doesn't seem to be the blower envy among 4.6 owners as there is among 5.0 and Mustang Cobra owners. For a fun daily driver, you can have a good time without a supercharger-on the other hand, a blower makes great street power and definitely has sex appeal. It's also a fair chunk of change, and in the end, a question each owner must decide on for himself.
Where the blower question is appropriate for bolt-on buyers is once again, will there ever be a blower on this car? If yes, then what kind of supercharger? It's important because there is little sense in dressing the engine with a bunch of bolt-ons that either must be removed or are supplied with the blower kit. That, and optimizing the supercharger combination calls for slightly different components than a naturally aspirated one will.
As examples, a throttle body, plenum, and 4.10 gears are great on a naturally aspirated Mustang, but if you later fit a Kenne Bell Twin-Screw blower, you'll find the kit comes with its own throttle body, eliminates the elbow, and makes so much torque that 3.73 gears are faster than 4.10 cogs, and you might even be happier with 3.55s, or happiest playing the cheapskate and staying with the free 3.27s. On the other hand, go with a centrifugal such as a Paxton or Vortech, and the big throttle body and elbow will support extra power, and those 4.10 gears will still pull the Mustang out of the hole until the blower boost becomes meaningful around 3,750 rpm.
At this point, the average owner has reached the practical end to his engine modifications. The fuel and ignition systems are quite good from Ford and don't need any help at the bolt-on (non-blower) level. That means the stock fuel pump and stock 80mm mass air meter ought to see you through the bolt-on stage. Of course, if you go past bolt-ons, you'll need to step up the fuel system, and possibly the ignition system if you really turn up the boost. But at 300 rwhp, the stock gear is OK.