Richard Holdener
October 12, 2012

As production powerplants go, the new 5.8L Shelby engine is one serious piece of hardware. Some may put it down to the simple application of displacement and boost, but that is, at best, only a portion of an extremely complex equation. Ford engineers applied a tremendous amount of technology to ensure that the increased displacement, boost, and power level measured up to rigorous production standards. The benefit to us mortals is 662 hp and 631 lb-ft of torque, and a foundation capable of supporting a whole lot more. We are literally salivating at the thought of a combination that started out with an extra 160 hp over the last Shelby!

Before getting to the inevitable Kenne Bell blower upgrade for the new GT500, we should take a quick look at what separates this Trinity version (also the top secret code name assigned to the first U.S. nuclear test) from the previous 5.4L Condor combination. Here at MM&FF, we have stressed time and time again that the best route to a powerful supercharged engine is to start with a healthy normally aspirated model. Then, any changes made to boost will be that much more effective. Ford threw pretty much all the bells and whistles at the new 5.8L, but it is the execution that sets the combination apart.

The first step was to increase displacement, taking the 5.4L to a full 5.8 liters, or 351 ci for those yet to embrace the metric system. Like the 5.0L 302, the 5.8L 351 displacement offered historical Blue Oval significance, especially for Cleveland, Midland, and Windsor Ford fanatics. The bore and stroke of the modern modular engine differs from those originals, but the shared displacement at least provides a link to the past. The extra displacement was achieved by increasing the bore of the 5.4L from 90.2 mm (3.55 inches) to 93.5 mm (3.68 inches). The already lengthy 105.8mm (4.165-inch) stroke remained unchanged. Given the restrictive bore center of the modular engine, the increase in bore size was only possible thanks to a new spray-bore process Ford calls Plasma Transfer Wire Arc, that replaced the iron cylinder liners with a ultra-thin (0.006-inch) cylinder coating.

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Inside the aluminum GT500 block, Ford modified the internals for the intended output. The increase in displacement was accompanied by an increase in the static compression ratio, too. The revised power output and attending cylinder pressure required a new (stronger) piston design. Mahle was given the nod to design forged slugs with the strength to withstand the elevated cylinder pressures and temperatures. The (just under) 3cc decrease in dish volume was combined with the (just over) 3mm increase in bore size to bump up the static compression ratio from 8.4:1 to 9.0:1. This should improve off-boost performance and efficiency. Minor revisions were made to the small end of the connecting rod and bearing material, as well as the overall balance of the forged-steel crankshaft (required from the change in piston weight).

To increase heat dissipation and piston life, the 5.8L is equipped with piston oil squirters. A great deal of research and development went into the design, placement, and flow of the squirters to ensure adequate and not excessive oil flow under all conditions. The 5.8L retained the Four-Valve cylinder heads with only minor revisions. The heads were treated to new Nimonic alloy exhaust valves equipped with Stellite rings on the seating surfaces. To better withstand the added pressure and heat generated by the 5.8L, the exhaust valve facing was also changed. To further enhance longevity, the 5.4L heads were also treated to an additional machining operation to improve coolant flow between the exhaust valves. The 5.8L aluminum block received a similar operation to route the coolant through the passage in the cylinder heads.

Unlike the 5.0L Coyote engine, the 5.8L does not require variable cam timing, and relies on the high-lift cams from the 5.4L Ford GT supercar. The Ford GT cams increase lift by 1.1 mm on the intake, and 1.4 mm on the exhaust over the GT500 cams. The GT heads and cams are combined with a blower upgrade from the M122 used on the previous GT500 to the 2.3L Eaton TVS.

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The bigger blower also received a smaller blower pulley (down from 3.06 to 2.71 inches), the result of which was an increase in peak boost pressure from as little as 8 psi on the original 5.4L to as much as 15 psi on the new 5.8L. The increase in discharge temperature is handled by a revised intercooler system that (according to Ford engineers) has doubled in cooling capacity. Toss in a larger blower inlet (increased by 33 percent over 5.4L), and you start to see the level of technology that went into making the new GT500 bigger and better--and we have just scratched the surface.

Cool stuff indeed, but as impressed as we are in stock trim, we just couldn’t leave it that way. Here at MM&FF, we are all about pushing the envelope, and having such impressive hardware to start with meant the rewards would be than much sweeter. Since Ford saw fit to offer the GT500 with factory forced induction, we knew the engine was plenty stout. The list of specifications reads like a wish list for anyone building a modified modular plant. All we had to do was replace the one component that stood in the way of this engine making crazy power, namely the factory TVS supercharger.

Sure, the 2.3L is a sizable blower, but ultimately, it is the limiting factor to serious power production. Ford engineers designed the system to produce the desired power goal; the 2.3L blower was never designed for four-digit power levels. What the 5.8L GT500 needed was a larger, more efficient supercharger. Enter the Kenne Bell 3.6L Twin-Screw.

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Truth be told, Kenne Bell offers its Twin-Screw supercharger in a variety of different displacements. Though smaller in displacement than the 3.6L used in this test, the benefits of the 2.8L include fitment. The 2.8L will fit under the stock GT500 hood, while the larger 3.6L requires a Super Snake (or other aftermarket variant) hood for proper clearance. Despite the fitment issue and the fact that the 2.8L is capable of supporting over 1,000 hp, we suspect most GT500 owners will be stepping up to the 3.6L. To meet our deadline, we were forced to run this test in an accelerated fashion. Look for even bigger power levels coming your way.

Run in stock trim, this supercharged 5.8L pumped out 603 hp and 604 lb-ft of torque as measured on the Dynojet. Given our limited time schedule, we were unable to perform the usual battery of tests on the stock configuration. We know many enthusiasts will be cranking up the boost, adding air intakes and headers, and dialing in the tune. There is certainly more power to be had before replacing the stock supercharger, but if you are looking for big power, you will need a bigger blower. We suspect guys will easily exceed 700 rwhp and find ways to top 750 rwhp with the stock blower, but the ease at which we bested this level makes a compelling argument for upgrading the supercharger.

That Shelby offers the 3.6L Kenne Bell supercharger on the highest power option for the Super Snake and GT1000 programs is a testament to the power and reliability of the Twin-Screw system. With our baseline out of the way, off came the stock 2.3L TVS blower and on went the Liquid-Cooled, 3.6L from Kenne Bell. The blower upgrade retained the factory air-to-water intercooler, meaning boost will be properly chilled before making its way into the combustion chambers. The blower swap also retained the factory 55-lph injectors, augmented only with a 20V Boost-A-Pump. According to Kenne Bell, the stock fuel system (with BAP) will support over 950 rwhp! Once the Kenne Bell 3.6L blower upgrade was installed, we made a few minor changes to the system. Realizing the stock air intake would be restrictive, Kenne Bell designed its own 5-inch inlet system. Getting cool air to the engine is critical, and will be a chore given the confines of the engine compartment. The factory openings are helpful, but inadequate at the revised flow levels.

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The revised air intake system includes a massive filter and 5-inch inlet tube, with mounting provisions for the MAF electronics, feeding a dual-75mm throttle-body (up from the stock dual-60mm unit). All of this was hooked to the Kenne Bell Mammoth intake manifold (feeding the blower) to ensure uninterrupted airflow to the liquid-cooled 3.6L blower.

Equipped with the stock crank pulley and 3.0-inch blower pulley, the Kenne Bell supercharged 5.8L pumped out almost 20 psi of boost. The result was a jump in output from 603 hp and 604 lb-ft to 801 hp and 711 lb-ft of torque. Where the stock supercharger struggled to reach 600 lb-ft, the Kenne Bell combo exceeded 600 lb-ft from 2,300 rpm to 7,000 rpm! Best of all, we have just scratched the surface of this combination. Check back with us next month when we get the Kenne Bell to really start whistling.

5.8L GT500-Stock 2.3L TVS vs. Kenne Bell Blower Upgrade

How do you not absolutely love a bone-stock modular engine that pumps out 600 rwhp and a like amount of torque? As impressive as the new 5.8L is, check out what happens when you plop on the Kenne Bell 3.6L blower and crank up the boost. If there is an easier way to add 200 hp, we don't know about it. Better yet, the 3.6L is just getting started, as we know there is even more power waiting in the wings just begging to be unleashed. For now, we are content with a 5.8L GT500 pumping out just over 800 rwhp and 711 lb-ft of torque, but look for us to change that situation in the next issue.

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18 Equipped with the liquid cooled 3.6L Kenne Bell blower upgrade, the 5.8L Shelby pumped out 801 rwhp and 711 lb-ft of torque at just under 20 psi. Check back with us next month when we make this bell whistle even louder.