Harry Hruska, founder of HPT Turbocharger, has been at the forefront of turbo technology for decades. In the 1980s, he helped revolutionize the performance turbo market as the founder of Precision Turbo & Engine, with innovations that set over 300 world records. After learning the ropes at Garrett Turbochargers and then building Precision, Hruska eventually sold that company. After selling, he was able to return to the tracks and realized how much he missed the direct racing involvement. Eventually, he launched HPT Turbocharger as a new chapter focused on custom development.

“I had less and less time to go to the races and meet customers in my last days at Precision, and that’s not how I wanted to finish,” Hruska recalls of stepping away from the big corporate role. At the urging of former customers, he returned to the industry.

“I found out that I really loved what I did at the beginning, and I’m back to loving what I do now which is developing turbos and working with customers”. The name HPT, by the way, is just a brand label. “Some people say it stands for Harry’s Performance Turbos. No, it’s just HPT Turbocharger. I always keep my name out of it,” he quips.

Size matters. An HPT F5 series turbo (left) dwarfs an F2-series unit (right), illustrating the range from compact street units to massive race turbos.

Turbocharger Sizing: What Does the F1 Through F5 Designation Mean?

HPT uses a naming system from F1 through F5 (a playful nod to the Fujita tornado scale) to categorize its turbo lineup. Each step up corresponds to a larger turbo frame and higher horsepower potential. The range runs from the small F1 units (for UTVs, motorcycles and big-power street builds) up to the mighty F5 series for 1,800 to 3,200-plus-horsepower dedicated race engines.

For instance, in our latest edition of Horsepower Wars, teams are both running HPT F3 turbos aimed at about 1,300 horsepower from 5.0- and 5.3-liter V8s. The F3 housing size is similar to the “T4” sizing of other brands, and even offers T4 flanges on the turbine housing as an option.

 Area Over Radius and How It Affects Choosing the Right Turbo

Another key spec to any turbocharger is the Area/Radius ratio (A/R), essentially the size of the turbo housing relative to the turbine wheel. Hruska describes A/R as “a ratio between the diameter of the turbine wheel and the area of the inlet throat of the turbine housing.” In simple terms, it dictates the trade-off between low-end response and top-end power.

A smaller A/R means a tighter housing that spools up the turbo faster (full boost at lower RPM), but it can create backpressure at higher RPM that stifles top-end power. A larger A/R flows more freely for better peak horsepower at high RPM, but generally takes more exhaust energy (meaning a higher engine RPM) to reach full boost. HPT’s Quick Spool Technology ball-bearing system helps mitigate this compromise, allowing even a big turbo to spool like a smaller one.

In our Horsepower Wars competition, our engine builders discovered they had very specific needs when it came to turbocharging small cubic-inch engines (5.0 liters) at around 9,000 rpm. In response, HPT Turbochargers was able to come up with customized F3 turbos that fit the unique configurations of our competition engines.

Mixing Different Compressor and Turbine Sizes

Not all turbochargers use exactly matched compressor and turbine wheels. Sometimes one side is sized differently to fine-tune performance. Hruska emphasizes that the two halves of the turbo must work in harmony. “The relationship between the compressor wheel and the turbine wheel has to be a marriage,” he says. Each must complement the other. Finding the ideal pairing is complex, involving wheel diameters, trims, blade counts, and more. This is where HPT’s expertise comes in.

“After 38 years of doing this, that’s a strength we have because we understand the relationships,” Hruska says of optimizing compressor and turbine combos. “We don’t expect the customer to understand everything. That’s our job to help them navigate.” There’s a lot of science going on here, so don’t feel like you’ve got to understand it all yourself — or depend on some anonymous person on a message board. HPT’s ability to custom-tailor those internals is a key advantage over one-size-fits-all solutions.

Turbine Flange Types And Turbocharger Performance

Turbo housings come with different flange types for mounting, commonly a V-band clamp or one of the various standardized four-bolt flanges. Does one style perform better? Hruska says it’s mainly a matter of packaging and proper sizing. He actually breaks out spreadsheets to calculate header and collector dimensions and ensure there are no sudden area changes into the turbine.

Normally, performance enthusiasts struggle to find the balance between choosing a smaller turbo that spools quickly or a larger one capable of moving tons of air into the engine. But HPT Turbochargers’ Quick Spool Technology system — headlined by super-efficient ball bearings — means bigger turbos can spool more quickly than ever, giving you the best of both worlds.

“Any time we expand the gases and then recompress them, we lose energy,” he notes of the importance of a smooth flow path. As long as the turbo inlet and exhaust manifold are well matched, either flange style can work equally well. “You almost can’t do it wrong unless you do something really crazy, like put an expansion chamber way before the turbo,” Hruska laughs, recalling an instance where an overly large header collector killed performance.

So, for those keeping tally at home, the two turbochargers being used on the LS vs. Coyote 3 engines are essentially identical in performance, given that the only difference between the two turbochargers are the turbine flanges; one is a V-band and the other is a T4 rectangular four-bolt flange.

Turbocharger Internals are Important

Often, it’s the stuff on the inside you can’t see that’s the key to making everything work. For example, Hruska spent nearly two years developing a proprietary bearing that pushes the envelope of efficiency (even the bearing manufacturer was hesitant to make it at first). The payoff is exceptional spool speed and durability. No bargain turbo can replicate it. “The low-buck guys don’t have that bearing, and they don’t have a turbocharger that, if you just spin it with your finger, it’ll turn longer than you can hold your breath,” he points out.

Another major advantage of HPT is the knowledge and support behind the product. Hruska and his staff have a deep motorsports heritage — they’ve raced and tuned everything from Pro Mod drag cars to road racers — and they make that expertise available to customers. “For the last literally 40 years, we’ve been helping people get down the racetrack. You can’t get that from most companies,” Hruska says about HPT’s hands-on approach.

The shape of the impeller is critical to moving air efficiently without adding any unnecessary heat. CNC billet units are the ultimate in precision.

If a customer is having trouble, the team can help diagnose the entire combination. “Many times if the turbo isn’t making power, we’ll start diagnosing what’s going on with the engine,” he notes. Sometimes the turbo will get blamed when the real bottleneck — whether it’s a weak ignition, fuel delivery issue, or something else — may be tougher to diagnose.

Finally, HPT’s customer service philosophy is refreshingly focused on long-term success. Hruska prefers to speak with buyers to ensure they get the right turbo for their needs. To that end, the HPT Turbo team put together a turbocharger that isn’t on their website in order to meet the ruleset of LS vs. Coyote 3, taking the compressor side from its F3 7675 turbocharger and mating it to the turbine side of the F3 7880 for a custom 7680 turbo for our competitors.

“Talking to us is the best way to get the solution. Very rarely does someone just order a turbo on the website and we haven’t talked to them,” he says. “Our deal is to the finish line, not [just] from when we get it. I’ve made all the money I need to make. Now it’s just taking care of people.”

Although a big turbo bolted to the front of an engine is often the headliner, it is only part of a complex system that all must work together to produce maximum horsepower. It is important if you are having problems, to be able to work with experts who can help you find the real source of a problem and not simply suggest band-aids.