Richard Holdener
June 3, 2014

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.