LISTEN TO THIS SHELBY GT350R HIT 8,200RPM!

John Hennessey’s shop strapped a Shelby GT350R to the dyno wearing its new HPE850 supercharger package, running on Shell V-Power 93 octane, and posted a pull that added 311 rear-wheel horsepower and 193 lb-ft of torque over the car’s naturally aspirated baseline. The resulting graph, a dual-scale readout where the horsepower and torque curves cross around 7,400 rpm, briefly confused viewers before the final number sank in. Watch the pull to see what boosting a flat-plane-crank Voodoo V8 actually looks like on the rollers.

A dyno chart is supposed to settle an argument, not start one. When John Hennessey’s shop ran a Shelby GT350R through a pull with its new supercharger package installed, the resulting graph confused viewers before it impressed them, a dual-scale readout where horsepower and torque lines crossed at a spot nobody expected, prompting one commenter to call it flat-out Holy Torque Curve, Batman. The number that eventually emerged put this GT350R in territory the naturally aspirated factory version never touches. Here’s what the numbers actually mean, and why one detail about the engine’s flat-plane crank made this pull unusually dramatic to watch.

The HPE850 Package Behind the Numbers

This build is Hennessey Performance’s HPE850 supercharger upgrade for the Shelby GT350R, run on Shell V-Power 93 octane fuel during testing. According to Hennessey’s own figures, the supercharger added 311 rear-wheel horsepower and 193 lb-ft of rear-wheel torque over the car’s naturally aspirated baseline, a gain that, stacked on top of the GT350R’s already potent factory output, is what pushed the total figure toward the 787 rear-wheel horsepower mark referenced in the video’s title.

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What 787 Rear-Wheel Horsepower Means at the Crank

One commenter did the math and put the crank-equivalent figure at roughly 938 horsepower, accounting for typical drivetrain loss on a manual-transmission platform like the GT350R. That kind of number moves this car from quick factory Mustang into supercar-adjacent territory, especially notable given the GT350R’s factory 5.2-liter Voodoo V8 was never designed with forced induction in mind.

Why the Torque Curve Confused Viewers

The dyno readout used a dual-scale graph, plotting horsepower and torque on separate axes rather than a single shared scale, a common dyno software convention, but one that visually distorted where the two curves appeared to intersect. One viewer flagged this directly, noting the crossover point looked like it landed around 7,400 rpm and initially worried something was wrong with the pull, before realizing it was simply how the chart was scaled.

The Voodoo Engine’s Flat-Plane Crank Factor

The GT350R’s 5.2-liter V8 uses a flat-plane crankshaft, a design borrowed more from European sports cars and race engines than typical American V8s, prized for how high it revs and how sharp its throttle response feels, but also historically trickier to boost reliably than a cross-plane V8. Hennessey’s HPE850 package getting nearly 800 rear-wheel horsepower out of that architecture without the engine falling apart on the dyno is a meaningful engineering achievement, not just a bolt-on power adder.

Hennessey’s Track Record With Forced Induction

Hennessey Performance has built its reputation over decades on squeezing four-digit horsepower numbers out of factory platforms, and the shop’s Tuner School program, a classroom built around an in-house chassis dyno and quarter-mile dragstrip, reflects how much of its business is built around teaching, not just building, this kind of forced-induction work. The HPE850 GT350R package fits squarely into that history of taking an already extreme factory car and pushing it further.

Why Hennessey Chose the GT350R Specifically

The GT350R’s track-focused chassis, stripped-down interior, and more aggressive aerodynamics made it the natural candidate for a supercharger package aimed at serious performance rather than daily comfort, and Hennessey’s decision to build the HPE850 around this specific variant reflects that. A standard GT350 buyer prioritizing comfort features would likely find the R’s harsher ride and lack of a back seat a harder sell, even with nearly 800 rear-wheel horsepower on tap.

How This Fits Into Hennessey’s Broader Mustang Lineup

The HPE850 sits within a family of Hennessey Mustang packages spanning multiple power levels and platforms, from the standard EcoBoost to the GT and now the flat-plane-crank GT350R. Each package is built around the specific engine architecture it’s paired with, which is why the GT350R’s HPE850 supercharger kit differs mechanically from what Hennessey offers on the pushrod-based GT, reflecting the added engineering complexity of boosting a high-revving flat-plane V8 safely.

What Happens to Reliability at This Power Level

Adding roughly 300 rear-wheel horsepower to a factory engine raises legitimate questions about long-term reliability, particularly for a flat-plane-crank design not originally engineered around forced induction. Hennessey’s testing regimen, built around the in-house dyno and dragstrip at Tuner School, exists specifically to validate that a package like the HPE850 can survive sustained use rather than just a single headline-grabbing pull, which is part of why the shop backs its builds with its own warranty coverage.

What Owning an HPE850 GT350R Actually Costs

A supercharger package capable of adding roughly 300 rear-wheel horsepower to an already $63,000-plus track-focused Mustang does not come cheap, and Hennessey’s HPE850 kits typically run well into five figures once installation, tuning, and supporting fuel system upgrades are factored in, on top of the GT350R’s own steep purchase price. That combined cost puts a build like this well outside what a typical enthusiast can casually justify, which is part of why documented dyno pulls like this one matter so much to the small community of owners actually considering the upgrade: verified, third-party-witnessed numbers are the closest thing available to proof that the investment delivers what it promises. For a car already positioned as one of the more expensive, track-oriented Mustang variants Ford has ever sold, adding a forced-induction package on top pushes the GT350R into a category of build that is less about daily practicality and more about chasing a specific, extreme performance ceiling most factory Mustangs never approach, regardless of trim or options.

Why Flat-Plane Cranks Are Rare in American V8s

Most American V8s, including nearly every other Mustang engine Ford has built, use a cross-plane crankshaft, valued for smoother low-end torque delivery and a deeper exhaust note that most domestic buyers expect. Ford broke from that tradition specifically for the Voodoo engine to chase the high-revving character and rotational balance more common in Ferrari and Formula 1-derived designs, a deliberate engineering trade-off that prioritized top-end performance and throttle response over the low-rpm torque character most American V8 buyers are used to, which is exactly what made adding forced induction to it, safely, at Hennessey’s scale, a genuinely uncommon technical challenge worth documenting on video.

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