Ford Mustang Twin Turbo – 526 Cubic Inches

A 3.91 at the eighth-mile stripe on a drag radial that looks almost too small for the job isn’t something a stock small-block Mustang was ever meant to produce, but that’s exactly what Josh Klugger’s Fox Body delivered in qualifying. Behind that number sits a 526 cubic inch stroker short block, twin 102mm turbochargers, and a FuelTech FT500 engine management system working together to survive cylinder pressures the factory 302 was never designed for. Read on to find out what it actually takes to build a small block that can run numbers like that.

Three-point-nine-one at the eighth-mile stripe on a tire that looks like it wandered off a bicycle — that’s not a number a stock small-block Mustang was ever built to produce, and yet that’s exactly what rolled off the trailer at this event. Getting there means feeding a small block enormous amounts of air, more than any naturally aspirated combination could ever supply, and somebody decided the only way to do that right was with two turbochargers instead of one. The engine bolted between the shock towers isn’t stock displacement either. So what does it actually take to build a Fox Body that runs times like that on a track meant for cars several times its size?

Three-Point-Nine-One Is Not a Beginner’s Number

An eighth-mile pass in the low 3.90s translates to a full quarter-mile run deep into the 6-second range for a car built around a small-block Ford platform, territory that’s normally reserved for purpose-built Pro Mod and radial-tire cars rather than something that started life as a factory Fox Body. Josh Klugger backed up that 3.91 in qualifying without drama, which in eighth-mile drag racing is often the harder achievement — plenty of cars can run a number once and never repeat it.

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526 Cubic Inches Where a 302 Used to Live

Fox Body Mustangs left the factory with a 302 cubic inch small block, and this build has grown that displacement all the way to 526 cubic inches — a stroke and bore job that leaves almost nothing of the original short block behind. That much displacement gives the twin 102mm turbochargers a far larger volume of air to work with on every cycle, which matters enormously when the goal is spooling turbochargers that size quickly enough to matter in an eighth-mile pass rather than a long, lazy top-end pull.

Small Block, Enormous Turbos

Twin 102mm turbochargers are an extreme sizing choice even by drag radial standards — units that large typically need serious engine speed and boost pressure to spool efficiently, which is exactly why a build running this combination almost always pairs them with a fully built, stroked short block rather than anything resembling a stock long block. The trade-off is real lag down low in exchange for genuinely massive top-end airflow once both turbos come fully online and start making real boost.

Why FuelTech Controls Make or Break a Build Like This

A FuelTech FT500 engine management system gives the tuner the ability to manage boost, timing, and fuel delivery in real time across an entire launch, which matters enormously on a combination pushing this much cylinder pressure through a comparatively narrow drag radial tire. Get the tune wrong and the tire simply can’t hook; get it right and the result is a 3.91 at the eighth-mile stripe on a tire width that looks almost comically undersized for the power going through it.

The Tire Doing an Impossible Job

A drag radial narrow enough to look borrowed from a much smaller car is being asked to translate several thousand horsepower worth of turbocharged torque into forward motion without spinning into a haze of smoke. That’s a suspension and tuning problem as much as a tire problem — weight transfer, launch RPM, and boost curve all have to be dialed in together, or all that displacement and turbo capacity just turns into wheelspin instead of a clean 3.91.

Building a Short Block That Can Survive This

Stroking a small block out to 526 cubic inches and bolting on twin 102mm turbochargers means the internals have to survive cylinder pressures nowhere near what a factory 302 was ever engineered for — a forged rotating assembly, priority-main oiling, and a stout head gasket setup are the bare minimum before boost even enters the conversation. None of that shows up in a quarter-mile time slip, but all of it is the reason this engine survives repeated full-throttle passes instead of grenading on the second run.

The Fuel System Has to Keep Up Too

Feeding a 526 cubic inch turbocharged small block enough fuel to stay safe at wide-open throttle is its own engineering problem, separate from the turbos and the short block entirely — high-flow injectors, a return-style fuel system capable of supporting serious boost pressure, and a pump sized well beyond anything a factory Fox Body ever needed are standard equipment on a build chasing numbers like this. Running lean for even a fraction of a second at this power level is usually how engines like this end up in pieces.

Chassis and Suspension Do the Unsexy Work

Runs like a 3.91 only happen with the fundamentals dialed in underneath the car — suspension geometry tuned specifically for weight transfer under hard launch, a converter matched to the turbo combination’s powerband, and a chassis reinforced to survive repeated full-throttle launches without flexing or breaking parts. It’s a reminder that in drag racing, the engine gets most of the attention, but the chassis and the tune are just as often what separates a good pass from a broken one.

Why Fox Bodies Keep Showing Up at Events Like This

The Fox Body platform has stuck around in drag racing circles for decades because it’s light, simple, and endlessly adaptable — a body style originally built for economy and modest V8 power that turned out to be an ideal starting point for exactly this kind of extreme turbo build. Decades after the last one rolled off the line, Fox Bodies are still showing up at record-chasing events wearing engines and turbo combinations nobody at Ford ever could have imagined for the platform.

What a 3.91 Actually Represents

A number like 3.91 at the eighth mile isn’t really about one single part — it’s the sum of a 526 cubic inch short block that can survive the cylinder pressure, twin 102mm turbochargers big enough to feed it, a FuelTech system smart enough to manage all of it in real time, and a chassis built to put the whole combination down on a tire that looks far too small for the job. That’s what it actually takes to run those kinds of numbers, and it’s exactly why passes like Josh Klugger’s keep drawing a crowd.

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