Richard Holdener
June 3, 2014

Whenever someone utters the words, “Hey, I have an idea,” it usually falls into one of two categories. Category 1 is for those inspiring, grand gestures with the strength to alter all of humanity. Simple statements like, “Let’s put a man on the moon,” “Let’s end apartheid,” or “I found the cure for cancer.” Category 2 is home to those on a slightly smaller, and decidedly dumber scale—“Let’s jump off the roof and use a bedsheet as a parachute,” or “Let’s pull this office chair behind the truck down a crowded street and get a reaction on Youtube.” That sort of thing.

Thus, we came up with the idea to illustrate the strength of the stock 351W short-block by subjecting it to obscene boost levels.

The original idea was to clear up Internet myths regarding the strength of a stock Ford block and cast rotating assembly. We’ve all heard the stories—cast cranks, rods, and pistons will only withstand 8-, 10-, or maybe 12 psi. The fact is these components have no way of recognizing boost pressure. Actually, you might be surprised just how much power (and boost) the stock components can take before giving up the ghost. The obvious exception is the notoriously weak factory 5.0L block, but knowing this, we chose to run our boost test on the larger and stronger 351W.

The idea was simple. Take a stock 351W short-block from the wrecking yard; add heads, cam, and intake; and then start adding boost until something breaks. You might question adding the aftermarket components, but we wanted more than just big boost with our Big Bang—we wanted big power numbers to go with it. Boost multiplies the output of the normally aspirated motor, so we wanted to start with something that made more than 250 hp. This also gave us the opportunity to freshen up the junkyard jewel, since we had no idea what abuse it had endured prior to its revival.

The injected 5.8L (351W) test motor was pulled from the engine bay of an F-250 truck. The hydraulic-roller motor made life easy for us, since all we had to do was replace the cam. The motor was given a quickie ball-hone and minor surfacing to ensure good head sealing. The crank was polished and given fresh bearings, but the stock rings were cleaned and reused after increasing the ring gap to 0.035 inch.

The majority of piston destruction can be attributed to one of two issues, detonation from improper tuning, or insufficient ring gap. The extra heat generated in forced-induction applications will cause to rings to expand. The combination of excessive expansion and insufficient ring gap can cause the rings to butt together and stick momentarily in the bore. The result of this is a snapped ring land on the piston. The resulting broken piston was not due to inherent weakness (metallurgy or otherwise), but rather insufficient ring gap.

Hey, I think we are going to need one of these (if we want the 351 to live a long life).

The stock short-block was reassembled using the stock cast crank, rods and pistons, then augmented with 1⁄2-inch ARP head studs and Fel Pro 1011-2 head gaskets. With our test mule ready, we added the first of the power producers, namely heads, cam, and intakes. Having just run the AFR 205 heads previously on our twin-turbo, carbureted 347, they were perfect for this 351W. The heads offered exceptional flow (331/235 cfm), small (58cc) combustion chambers and a 2.08/1.60 stainless valves package. The AFR heads also featured a spring package that offered sufficient rate and coil bind clearance for our sub-0.600-inch lift hydraulic-roller cam.

Crane supplied our hydraulic roller cam, but it could not be installed until we cured a piston-to-valve clearance issue. The stock dished pistons featured plenty of clearance using the factory cam and stock valve sizes in the iron heads, but the added duration and larger intake valves in the AFR heads required additional clearance. After marking the piston with clay, we used a Dremel rotary tool to notch each piston for clearance. It wasn’t pretty, but our cam now had 0.060-0.070 piston-to-valve clearance.

We finished off the power producers with a TFS-R intake combo, a Holley 75mm throttle body, and 83-lb/hr injectors. Run on the engine dyno with a Holley HP EFI system and Hooker long-tube headers, the mild 351W produced 410 hp at 5,800 rpm and 406 lb-ft at 4,400 rpm.

We had just run the twin-turbo kit from CXRacing on the carbureted 347 stroker, now we applied it to the larger (but less powerful) 351W. We did, however, make a few changes to the turbo system to facilitate our test.

The first change was to replace the air-to-air intercooler with an air-to-water unit. The next change involved replacing the T-3–based GT35 turbos with larger T-4-based T76 models. This required making adapters that stepped up the T3 flanges to larger T4 flanges to accept the 76mm turbos. Capable of exceeding 700 hp each, we had more than 1,400 hp worth of turbos for the 351W.

Because we had extra wastegate springs on hand, the CXRacing wastegates were replaced by a set of Hyper-Gate 45s from Turbo Smart. We had 14-psi springs and the ability to take boost even further with a manual wastegate controller. Turbo Smart also supplied a Race Port blow-off valve. The remainder of the twin-turbo kit (tubing, couplers, and clamps) to supply the necessary boost to the awaiting 351W came from CXRacing.

Naturally, we started off slowly and worked our way up. We replaced the pump gas with 118-octane Rocket Brand race fuel and dialed back the total timing from 35 degrees to just 20 degrees. The intercooler was fed dyno water (there was more power to be had with ice water, but it is a hassle when you have to make 60-70 dyno pulls).

Starting at 7 psi, the turbo 351W produced 631 hp and 608 lb-ft of torque, while stepping up to 10.5 psi brought 719 hp and 687 lb-ft of torque. The stock crank, rods, and pistons were all still in place, so we cranked up the boost to 12.6 psi—the 5.8L pumped out 790 hp and 776 lb-ft of torque.

01. The stock dish pistons in the 351W required some minor machining to provide adequate piston-to-valve clearance. A Dremel rotary tool made short work of the cast pistons to provide the necessary clearance.

02. We replaced the stock cam with a Crane hydraulic roller. The Crane cam offered a 552/563 lift split, a 228/232 duration split, and 114-degree LSA.

03. Crane also supplied a double-roller timing chain for the 351W.

04. Since we planned on cranking up the boost, we augmented the Windsor with ½-inch ARP head studs and Fel Pro 1011-2 head gaskets.

05. Having had such great success on a previous 347, we installed a set of AFR 205 Renegade heads on the 351W. The AFR heads offered exceptional airflow and a thick deck to ensure sealing under boost.

06. Thanks to complete CNC-porting job, the AFR heads offered exceptional airflow, peaking at 331 cfm on the intake and 235 cfm on the exhaust.

07. The AFR heads featured a 2.08/1.60-inch stainless valves and a spring package that offered sufficient rate and coil bind clearance for our 0.560-lift Crane cam.

08. Our intake choice for the 351W was a TFS-R upper and lower. Here the lower was installed onto the awaiting long-block.

09. The TFS-R upper intake featured shorter runners to optimize power production higher in the rev range. On this application, we were not interested in low-speed power production or the better choice would have been the long-runner Track Heat or Street Burner intakes.

10. The two-bolt bottom-end was all stock, including the original rotating assembly, high-mileage oil pump, and pick-up.

The 800hp mark came and went at 14.6 psi, and the power numbers peaked at 943 hp and 901 lb-ft of torque at 17.8 psi. Things were getting serious! Another 2 psi brought 974 hp before cresting 1,000 hp with a peak of 1,023 hp at 21.5 psi, but this is when things started to unravel.

We managed to coax 1,054 hp out of the beast on one of the runs, but we were out of adjustment on the manual wastegate controller and had used up our supply of Turbo Smart wastegate springs. Daylight had long since disappeared, and though Turbo Smart was less than 10 minutes away (to secure stiffer wastegate springs), it had already closed for the day.

It was decision time and our choices were few. We could call it a day and be happy with a running, twin-turbo 351W wrecking-yard motor that just produced 1,054 hp and 1,033 lb-ft of torque. Or we could wait for Turbo Smart to open in the morning and secure the stiffer springs to properly increase the boost pressure and find the power limit of the combination. Or … “Hey, I have an idea. Let’s …,” which you may have guessed is the route we took.

Swapping over the boost reference lines to the top of the wastegates effectively closed them for good. Our “good” idea was to then control the boost pressure with the throttle during the dyno test.

Much like the rooftop and bedsheet experiment, our parachute never opened. With no wastegates to control boost, the boost pressure rose rapidly. Though we attempted to keep it near 20 psi at the start, the difference between some boost and all of the boost was a matter of milliseconds.

Before we knew it, the high boost extinguished the spark and literally shut down the motor—not good. After a few failed attempts, we finally managed to anticipate the situation and gain control, but the results were less than spectacular.

Rather then keep boost at a reasonable level, our throttle adjustments pulled away boost and power by the truckloads, dropping power production from 1,000 hp to 600 hp, then back up past 1,000 hp after adding more throttle, and so it went.

As if 1,000hp runs weren’t enough, the stock internals quickly grew weary of our throttle-induced stupidity and decided it was time to put an end to all the madness. The internal Big Bang prompted a massive smoke cloud and drop in power (not caused by throttle manipulation) that signaled the official end to our twin-turbo 351W program.

A post mortem revealed piston, rod, and even crank carnage. Looking back, we recognize that exceeding 1,000 hp with stock internals was impressive, but we can’t shake the feeling that there might have been even more left in the 351W had the author not been an idiot.

11. CXRacing supplied a pair of drain fittings for the turbo kit. We drilled holes in the pan and installed the bulkhead fittings.

12. Holley supplied the 83-lb/hr injectors and HP EFI system, while Hooker supplied the 1 ¾-inch headers. The headers were used to run the 351W normally aspirated prior to installation of the twin-turbo kit. Note the MSD distributor and stock plug wires.

13. Run in normally aspirated trim, the low-compression 351W produced 410 hp at 5,800 rpm and 406 lb-ft at 4,400 rpm. Now we’re ready for boost.

14. The Hooker headers were replaced by the dedicated turbo manifolds. Clearance was actually very good, allowing use of the factory plug wires without fear of burning. Hoping to exceed 1,000 hp, we replaced the GT35-style turbos run previously on the carbureted 347 with T4-based T76 turbos.

15. The larger T4 T76 turbos from CXRacing required adapters to convert the supplied T3 flanges to the larger T4 flanges.

16. The supplied air-to-air intercooler was replaced with an air-to-water intercooler. Supplied by CXRacing, the air-to-air intercooler featured a dual-inlet, single outlet, making it perfect for our injected Windsor.

17. Turbo Smart stepped up with a pair of 45mm, Hyper-gate wastegates. Even with our spring combinations and manual waste gate controller, we did not have enough boost to damage the stock internals-though we did find a way!

18. To eliminate the pressure spike that accompanies lifting off the throttle at maximum boost and rpm, Turbo Smart also supplied a Race Port blow-off valve.

19. Running boost to the 351W took us past 600 hp, 700 hp, and then 800 hp without even trying. Next came 900 hp and then 1,000 hp before running out of available boost. We managed to produce 1,054 hp and 1.033 lb-ft of torque before resorting to outside-the-box boost control.

20. The carnage that accompanied all the throttle manipulation. When she let go, she let go big bang style!

The graph illustrates the power curves offered in normally aspirated trim, then with the twin-turbos running 7 psi, 12.6 psi and 21.5 psi. The output jumped by nearly 200 hp with each successive increase in boost pressure. The 410 hp 351 eventually produced as much as 1,054 hp and 1,033 lb-ft of torque before we let all the magic smoke out.