I'v been back and forth on what I want to do. I had access to a free 4.6L long block out of a 1995 Thunderbird. That would be a downgrade from what I have before. Even if I used my PI cylinder heads, I didn't know the condition of the engine and didn't want to end up with the same as what I had before. I came across a heck of a deal on a complete engine out of a 2009 Mustang with 60K miles. It had a spun rod bearing. I eventually talked him into taking just $150 for it.
I tore the engine down, it was going to need a crankshaft and a complete bearing set but otherwise the block and cylinder walls were in excellent shape. I was excited to have an aluminum block 4.6L 3 valve that I was going to throw my 2 valve heads onto. With my heads, it would put me at a slightly high 11.5 to 1 compression ratio. I was also concerned if my heads would physically work with the 3 valve block. I found a buyer for both cylinder head/cam combos at $300, sold the valve covers for $50 BUT then someone offered my something I couldn't refuse. I ended up selling the WAP 4.6L aluminum block for $400. I feel like I made out like a bandit here.
Because of my mass profit, and my parts discount because of my employment at a Ford dealer, I decided to take advantage of an opportunity. Ford produced a limited run of brand new 5.4L short blocks. The short blocks come assembled, including new pistons, rods, bearings, caps, oil pump, an oil pan. I scored my engine for under a grand. With my heads, I would be pushing 11 to 1 compression ratio. The best part being the additional valve clearance because of the extra .120" piston to deck height over the 4.6L. Remember, I am running the Comp 262ah. I suppose I should contact them about degreeing the cams for a better center-line.
There are many disadvantages with going for a 5.4 in a Mustang. A bit a physics lesson awaits. The 4.6L is pretty square as far as bore x stroke. The 5.4L is basically a stroked 4.6L with the same size bore. The single biggest concern with a larger stroke engine is piston velocity. The piston has to move faster to cover a longer distance in the same amount of time. Historically, engines with a larger stroke to bore ratio are used in trucks because of the need for more torque and low rpm situations. An advantage of a bigger stroke is higher burning efficiency and less of a chance for pre-ignition and detonation. Big bore and short stroke are better suited for high RPM situations because of the lower piston velocity and better flow from the valves due to less shrouding. The 4.6L being almost square already have the higher RPM disadvantage here, but the 5.4L only makes it worse.
Aside from those physical disadvantages, intake and exhaust selection is lacking. The truck intakes are all aimed at torque production and are too huge to fit under a Mustang hood easily. As far as 2 valve setups, I will be using a set of adapters to install the 4.6L intake on my 5.4L. A now defunct company called HPS made an aluminum intake natively for a 5.4L in a Mustang. For those trying the 4 valve route, MMR makes adapters to installed a new coyote intake on Navigator 4v heads. No one mass produces a set of headers that fit this set up.
Many have been down this road before. Most say its not worth the effort to remove an otherwise good engine to do this swap. Obviously my reasoning is that I do not have a good engine. Comparing truck output specs to the original engine is pointless as is evidenced by comparing a 2004 Mustang 4.6L to a 2004 F150 4.6L. At the same time, those that have done it say its definitely worth it for a street car. The extra torque alone will be extremely noticeable. I'd say keep the gearing down to stock or at least under a 3.73 as the 5.4L doesn't like to rev as much as a the 4.6L. That goes for cam selection as well. What good does a stage 2 or 3 cam do for you if you can't consistently rev it out anyway? I always felt they were too high for a stock internal 4.6L, but they are definitely too high for a 5.4L. You'd kill all that newly found torque.
Lets get to building...