Ford’s New Truck Engine Has Excellent Performance Potential
The easiest and simplest way to build torque with an engine is to merely add displacement. That concept can be traced back to the earliest internal combustion engine builders and it’s still true today. When Ford decided that it needed big torque for its F-250 and larger trucks, they didn’t add a supercharger to a Modular engine. Instead, they designed a big pushrod, two-valve engine to get the job done. And there are a lot of Blue Oval hot-rodders who are very happy they did.
This story will pull up the details of this new engine, along with a few performance ideas that reveal this engine’s potential. It all starts with a healthy 4.22-inch bore and a nearly four-inch (3.976-inch) stroke that equates to 445 cubic inches (there is also a 6.8L/415-cu.in. variation that appeared for 2023 to replace the older 6.2L “Boss” V8, but for the sake of this article, we will focus on the 7.3L engine). Combine that with a modern combustion space that allows this production engine to run on 87 octane fuel using an efficient 10.5:1 compression ratio that makes 430 horsepower and 475 lb-ft of torque. That is 1.06 lb-ft of torque per cubic inch from an engine combusting cheap gas and rated with the conservative SAE correction factor. If all we did was apply the older, more traditional hot rod-style correction factor used in magazine stories, the difference is generally worth an added five percent. That would push this bone stock engine to just below 500 lb-ft of torque and right at 450 horsepower at the flywheel. That’s serious OE power that indicates this engine offers outstanding potential.
The cast-iron foundation for this 7.3L effort begins with a deep skirt design that uses four-bolt main caps that are laterally assisted with smaller cross-bolts. Bore spacing is defined as the distance between adjacent bore centerlines. Ford’s Modular engine family is restricted in bore diameter because of its limited 3.93-inch distance compared to the 7.3L’s elongated 4.530-inch spec. This is also 0.150-inch more than the traditional 351W. You might want to tuck that away in your favorite Ford spec chart sheet for future reference. This more expansive distance allows large bore diameters to increase displacement along with potentially longer strokes given the 7.3L’s 9.650-inch deck height.
Other notable features for the Godzilla block include piston cooling jets to keep the back sides of the pistons from overheating. This is an especially useful feature for anyone considering a supercharger for these engines. Topping it all off is a bellhousing pattern that is the same as the 4.6L, 5.0L, and 5.4L Modular engines. This should make transmission swapping much easier.
Modern V8 engines have all moved to four bolts per cylinder clamping but employ MLS head gaskets to seal the pressures in the cylinder. The 7.3L uses 13mm (1/2-inch) head bolts that increase the clamp load.
Because Ford knew this engine would be worked hard at lower engine speeds, the crankshaft is forged steel using eight crankshaft flange bolts to keep a tight grip on the power as it is applied to the drivetrain. The connecting rods are powdered metal to achieve a fractured cap design with a relatively large crankshaft main journal diameter to achieve a solid overlap between the main the rod journals for improved strength. The main journals are roughly 0.100-inch larger than Ford’s Coyote engine, while the rod journal diameters are duplicates of the Coyote.
Connecting rod length for Ford’s new engine extends to 6.139 inches which puts the rod-length-to-stroke ratio at 1.58:1. This measurement is just a number and does not reflect on power potential one way or the other. But the taller deck height does offer the potential to increase rod length should someone get the crazy notion to add some swing to the stroke to well over four inches. Plus, while we’re still in the lower end, the camshaft to crank center distance is a much expanded 5.430 inches, which not only offers more room for connecting rods for stroker applications but also moves the cam closer to the rockers to reduce overall pushrod length. This inherently makes the valvetrain stiffer, which is a good thing.
This photo of the factory front cover offers hints at how wide the factory accessory drive really is even without the alternator, power steering, and A/C pump. Several companies, including Indy Power Products and Holley have aluminum covers that will dramatically narrow this dimension, which will allow for easier swaps.
The cast hypereutectic Godzilla pistons are a typical production choice and the dished design keeps the compression in line. The ring package is somewhat conservative, based on more modern engines with thinner rings but engineers did trim the thickness from 1.5mm on the top ring to 1.2mm for the second while tightening the oil ring to 2.5mm. All of these efforts reduce friction which contributes ultimately to better fuel mileage and slight power improvements.
While lubrication systems usually don’t garner much attention, it’s clear that Ford put some effort into this system as it is certainly not traditional. There is a separate crank-driven chain located below the crankshaft centerline that drives a large, horizontal jack shaft located in a cast-aluminum mount placing the pump in the center of the oil pan amid a rather substantial casting. Because oil pumps with long inlet pipes (like the GM LS engine) suffer from oil pump cavitation issues at higher engine speeds, this may be one reason why Ford engineers chose to relocate the pump towards the center of the pan where it minimizes the draw pipe length and allows for improved pump performance.
This Ford cutaway engine photo reveals the relative depth of the stock oil pan. There are options for relocating the oil pump and shortening the oil pan from several companies that will help fit the engine into different applications.Photo: Ford Motor Company
Moving upward slightly, the aforementioned raised camshaft location benefits from a larger 60mm cam journal diameter that is substantially more robust than older Ford pushrod engines. The engine oddly employs smaller, 0.842-inch diameter hydraulic roller lifters, which is exactly the same diameter as the old small-block Chevy and newer LS engines. That may be a cost consideration. The lifters also use plastic sleeves that are similar to those used in the GM LS engines.
Valve timing for the hydraulic roller cam is 201/212 degrees at 0.050-inch tappet lift with valve lift on the intake at 0.539- and just under 0.600-inch on the exhaust. Adding duration would certainly push this engine’s power curve well up into the 6,000 rpm range where horsepower would clearly benefit. What helps this engine make serious torque is variable valve timing that swings through a broad timing range to advance the cam for low speed torque, and then retarding as rpm increases to benefit power at higher engine speeds. The aftermarket already has longer duration cams for quick power increases but these will generally need either a VVT-delete or at least limit the VVT travel in order to accommodate more valve lift with longer durations. There are also two separate chain tensioners to maintain tight cam timing numbers.
The 7.3L’s oil pump, pan, and lubrication system differ from tradition with this jackshaft-driven oil pump that is located in the middle of the oil pan. This makes the pan much deeper, which makes swapping the engine without altering the pump and oil pan a challenge.
One area where this big-inch motor takes advantage of its modern, stiffer valvetrain is with rocker ratio. This big motor uses investment-cast roller rocker arms with an aggressive 1.8:1 rocker ratio. Higher ratios multiply the lobe lift to benefit valve lift and improved airflow. However, higher ratios also challenge valvetrain stability, even at engine speeds below 6,000 rpm. Keeping with modern tradition, beehive valvesprings are also used and we noticed a much taller installed height in order to accommodate near 0.600-inch valve lift numbers.
Moving farther upstream, the aluminum two-valve cylinder heads clearly benefit from modern cylinder head technology starting with a very aggressive 8.8-degree valve angle that is also canted slightly at 1.8 degrees. This is not much different from the Ford 429/460-cu.in. engine family, but this new engine is considered to be closer to the small-block side of the Ford family tree. Benefitting from this more vertical valve angle are large 2.17-inch intake and 1.67-inch exhaust valves. Combined into a 62cc combustion chamber, the rectangular oval port inlets also seem to have pulled input from the Modular family with their more vertical entry angle intake port flange.