Performance Gains with the Hks Gts707 Turbo Kit on K-series: Real World Power Numbers

The HKS GTS707 turbo kit has carved out a strong reputation in the Honda tuning community as a well-engineered, high-output solution for K-series engines. Unlike generic turbo kits that require extensive fabrication and guesswork, the GTS707 is designed as a complete system, engineered to deliver predictable, repeatable power gains on both daily-driven and track-oriented builds. This article goes beyond basic dyno numbers to examine the real-world performance of the GTS707 on K20 and K24 platforms, the engineering decisions that make it effective, installation realities, tuning strategy, and how it compares to other popular turbo kits on the market.

Understanding the K-Series Engine Platform

Honda's K-series engine family debuted in 2001 and quickly became the gold standard for four-cylinder performance. Featuring a dual-overhead-camshaft design, i-VTEC variable valve timing and lift control, and an all-aluminum block with cast-iron cylinder liners, the K-series offers a remarkably strong foundation for forced induction. Displacements range from 2.0 liters (K20) to 2.4 liters (K24), and the engines are known for their high-revving character, efficient combustion chambers, and excellent aftermarket support. The head design, in particular, flows well from the factory, which reduces the amount of work needed to support turbocharging.

Stock K20 engines in applications like the Civic Si, RSX Type-S, and Integra typically produce around 140-160 wheel horsepower. A K24, found in the Accord, CR-V, and TSX, makes approximately 160-180 wheel horsepower in factory form. While these numbers are respectable for naturally aspirated four-cylinders, the real potential of the K-series is unlocked with forced induction. The closed-deck design of certain K20 blocks and the strong rod/stroke ratio of the K24 make both variants well-suited to power levels well beyond 300 wheel horsepower with proper supporting modifications and tuning.

High-revving capabilities: The K20 can safely rev past 8,000 RPM, while the K24 offers excellent torque with a slightly lower redline. Both respond well to upgraded valvetrain components for higher RPM operation under boost.
Strong aftermarket support: The K-series is one of the most heavily supported engine platforms in the world. Turbo kits, intake manifolds, fuel systems, engine management solutions, and forged internal components are widely available from dozens of reputable manufacturers.
Versatile for various applications: K-series engines have been swapped into everything from classic Civics to rear-wheel-drive tube-frame builds. The GTS707 turbo kit is specifically designed for chassis that originally housed a K-series, but the turbo itself can be adapted to custom setups as well.

The HKS GTS707 Turbo Kit: Engineering and Design Philosophy

HKS is a Japanese tuning house with decades of experience in turbocharger design and manufacturing. The GTS707 is a ball-bearing turbocharger that uses a lightweight, high-flow compressor wheel and a low-inertia turbine wheel. The "707" designation refers to the compressor wheel trim, which is sized to support up to approximately 400 wheel horsepower on a K-series engine while retaining excellent spool characteristics. This makes it a "street-friendly" turbo that does not require sky-high boost levels to produce satisfying power gains.

The complete GTS707 turbo kit for K-series includes the following components:

HKS GTS707 ball-bearing turbocharger: Features an investment-cast turbine housing with an integrated wastegate, reducing the number of potential exhaust leak points. The turbine housing is available in different A/R ratios, but the kit is typically spec'd for a 0.73 A/R to optimize the balance between spool time and top-end power on 2.0L and 2.4L engines.
Cast exhaust manifold: HKS engineers a dedicated cast-iron or high-nickel steel exhaust manifold for the GTS707 K-series kit. The manifold is designed with equal-length runners to promote even cylinder evacuation, which improves spool consistency and reduces the risk of cylinder-to-cylinder knock. The manifold also features a T3-style flange, allowing some end-users to swap the turbocharger without changing the manifold if desired.
High-capacity intercooler: The kit includes a bar-and-plate intercooler core that is sized to reduce intake air temperatures under sustained load. The intercooler uses cast aluminum end tanks with smooth internal transitions to minimize pressure drop. Inlet and outlet diameters are matched to the compressor outlet and throttle body piping.
Mandrel-bent charge piping: All piping is fabricated from 6061 aluminum with mandrel bends to preserve cross-sectional area and reduce turbulence. Couplers are reinforced silicone with four-ply construction and T-bolt clamps at all critical junctions.
Blow-off valve: HKS supplies its own Super Sequential blow-off valve, which is adjustable for different boost levels and intake configurations. This valve recirculates excess boost pressure during throttle closure, helping to maintain compressor wheel speed and reduce turbo lag between shifts.
Oil and coolant lines: The kit includes braided stainless steel oil feed and return lines, along with coolant lines if the turbocharger is water-cooled. Banjo fittings with restrictor orifices are used to control oil flow to the turbo cartridge.

One of the standout design features of the GTS707 is its emphasis on reducing turbo lag. The ball-bearing cartridge assembly has far less rotational inertia and friction than a traditional journal-bearing turbo, meaning it accelerates to operating speed with less exhaust energy. On a K24 engine, the GTS707 can reach 10 psi of boost pressure as early as 3,200-3,500 RPM under load. On a K20, full boost arrives slightly later due to the lower displacement, typically around 3,800-4,200 RPM depending on exhaust configuration and tuning.

Installation: What to Expect

Installing the HKS GTS707 turbo kit on a K-series engine is a significant project, but it is far more straightforward than a custom turbo fabrication effort. The kit is designed to bolt onto factory engine mounting points, use the stock engine position, and clear common chassis configurations such as the Civic, RSX, and Integra. That said, the installation still requires mechanical experience and the ability to tune the engine management system. As with any turbo conversion, it is recommended to start with a healthy engine. Compression and leak-down tests should be performed before installation.

Proper preparation of the engine and fuel system is critical to achieving reliable power with the GTS707. Do not skip injectors, fuel pump, and engine management upgrades.

Key Steps in the Installation Process

Remove the stock intake and exhaust components. This includes the airbox, intake pipe, exhaust manifold, catalytic converter or downpipe, and any associated heat shielding. On some chassis, it is easier to remove the engine mounts or lift the engine slightly to access bolts on the exhaust manifold.
Install the turbocharger and exhaust manifold. Apply a thin coat of anti-seize to the manifold studs. Torque the manifold nuts to the factory specification in a cross pattern. Use a new exhaust manifold gasket. Attach the turbocharger to the manifold flange using the supplied gasket. Torque the retaining nuts or bolts to the HKS recommendation (typically 35-40 ft-lbs for a T3 flange). Connect the oil feed line to the turbo. Do not over-tighten banjo bolts; use the proper crush washers.
Connect the intercooler and piping. Mount the intercooler core behind the front bumper or in the lower grille area. Use the provided brackets to secure it. Route the charge piping from the compressor outlet to the intercooler, then from the intercooler to the throttle body. Ensure that all couplers are fully seated and that the T-bolt clamps are oriented for easy tightening. Route the piping away from hot components and sharp edges.
Install the downpipe and exhaust system. The kit typically includes a downpipe that connects the turbine outlet to the vehicle's existing exhaust system. You may need to modify or replace the mid-pipe if it is restrictive. A full 3-inch exhaust system is recommended to keep exhaust backpressure low and maximize power output. Use a high-flow catalytic converter if emissions compliance is required.
Reinstall necessary engine components. Connect the intake pipe from the turbo inlet to the air filter. Reinstall any brackets, heat shields, and under-tray panels that were removed. Inspect all wiring and hoses to ensure they are not pinched or routed too close to hot surfaces.
Perform tuning to optimize performance. The stock ECU is not capable of supporting a turbocharged K-series engine. You will need a standalone engine management system such as a Hondata K-Pro, AEM Infinity, Haltech Elite, or MoTeC. Base maps are available from some tuners and may allow you to start the engine, but professional tuning is strongly recommended to achieve safe air-fuel ratios, proper ignition timing, and reliable power output. Do not attempt to drive the vehicle with a stock calibration after turbo installation.

Real World Power Gains: Dyno Results

Dyno results vary based on engine condition, fuel quality, tuning skill, altitude, ambient temperature, and supporting modifications. The numbers below are representative of well-tuned, healthy engines running 93 octane pump gasoline or a suitable ethanol blend. They are presented as wheel horsepower (WHP) measured on a Dynojet dynamometer, which reads approximately 10-12% higher than a Mustang or Dynapack dyno.

Stock K20Z3 (Civic Si) with GTS707 Kit

Peak power: 305-315 WHP at 7-8 psi of boost
Peak torque: 240-260 ft-lbs at 4,500-5,000 RPM
Boost threshold: 4,000 RPM
Redline: 8,000 RPM

At this boost level, the engine is still within the reliability margin for a stock internal K20. Many owners choose to run 10-12 psi, which pushes power to 340-360 WHP. At this point, the fuel system must be upgraded (larger injectors, higher-flow fuel pump). The stock clutch will also begin to slip at around 340 WHP and should be replaced with a stage 1 or stage 2 clutch kit rated for 400+ ft-lbs of torque.

Stock K24A2 (TSX or CR-V) with GTS707 Kit

Peak power: 340-360 WHP at 7-8 psi of boost
Peak torque: 290-320 ft-lbs at 4,200-4,600 RPM
Boost threshold: 3,500 RPM
Redline: 7,200 RPM (stock valvetrain)

The K24's larger displacement and superior low-end torque give it a clear advantage over the K20 in daily-driven turbo applications. The engine reaches full boost at least 500 RPM earlier, and the torque curve is significantly broader. With the GTS707 at 12 psi, power levels of 380-400 WHP are achievable. At that point, the stock connecting rods become a weak link on the K24A2, and forged rods are recommended if you plan to drive the car hard or increase boost further.

Built K20/K24 (Forged Internals) with GTS707 Kit

Peak power: 400-430 WHP at 15-18 psi of boost
Peak torque: 330-360 ft-lbs at 4,800-5,200 RPM
Boost threshold: 3,800-4,200 RPM (depending on displacement and header design)
Redline: 8,500+ RPM with upgraded valvetrain

Built engines with forged pistons, forged rods, ARP head studs, and upgraded valvetrain components can safely handle 18-20 psi on the GTS707. At this power level, the turbo is operating near its compressor map limit. Power curves tend to plateau around 430-440 WHP, and further increases in boost produce diminishing returns due to heat and backpressure. The GTS707 is not designed to support 500+ WHP; that is the domain of larger turbos such as the HKS GTIII-5R or a Garrett GTX3071R Gen II. For street and occasional track use, however, 400-430 WHP is an extremely potent and responsive package in a 2,800-lb Civic or Integra.

Tuning for Maximum Performance

Tuning is the single most important factor in achieving reliable power from the GTS707 kit. An untuned or poorly tuned engine can suffer from detonation, high exhaust gas temperatures, and premature turbo failure. The K-series responds well to ethanol blends such as E30 or E85, which offer higher octane and cooling effect, allowing more aggressive ignition timing and higher boost levels. For street cars on pump gas, conservative timing and a slightly richer air-fuel ratio (target 11.5:1 at peak power) provide a healthy safety margin.

Key tuning parameters to address:

Air-fuel ratio (AFR): Target 12.0-12.5:1 at cruise, 11.2-11.8:1 at full throttle under boost. Leaner than 12.0:1 at high load invites knock. Richer than 11.0:1 typically reduces power and increases fuel dilution of engine oil.
Ignition timing: Under boost, K-series engines typically run 12-16 degrees of timing at peak torque and 18-22 degrees at peak horsepower, depending on fuel octane and boost level. A good tuner will determine the borderline knock timing and then back off 2-3 degrees for safety.
Boost control: The GTS707's internal wastegate can be controlled with a manual boost controller or an electronic solenoid. Electronic control provides more precise boost ramping and better transient response. Keep peak boost within the turbo's efficient range (typically 18-20 psi max on the GTS707) to avoid excessive shaft speed and heat.
Fuel system capacity: The factory fuel pump and injectors are insufficient at any boost level. Upgrade to a 340 LPH or larger pump, and use injectors in the 750-1,000 cc/min range for pump gas or 1,000-1,300 cc/min for E85.

For those who are new to tuning, it is highly recommended to work with an experienced K-series tuner who has dyno-tuned GTS707 installations before. The cost of a professional tune (typically $500-$1,000) is trivial compared to the cost of rebuilding a damaged engine.

Reliability and Longevity Considerations

While the GTS707 kit is well-engineered, reliability ultimately depends on the quality of the installation, the health of the engine, and the conservatism of the tune. With proper maintenance, a GTS707-equipped K-series can be a reliable daily driver. However, certain components must be addressed:

Oil supply and return: The turbocharger requires a consistent supply of clean engine oil. Ensure that the oil drain line is routed downhill without any low spots or kinks that could cause oil pooling in the turbo center section. An oil restrictor in the feed line is often necessary to prevent over-oiling the ball-bearing cartridge, which can cause seal failure.
Cooling: The intercooler included in the kit works well for street use. If the car is driven in hot weather or on track, consider adding an oil cooler and a larger radiator. High under-hood temperatures can degrade silicone hoses and wiring over time.
Heat management: Wrap or coat the exhaust manifold and downpipe to reduce under-hood temperatures. Ensure that all wiring, brake lines, and plastic components are shielded from radiant heat. Turbo blankets are available for the GTS707 but must be installed carefully to avoid trapping heat and damaging the wastegate actuator.
Maintenance intervals: Shorten oil change intervals to 3,000-4,000 miles with a high-quality synthetic oil (5W-30 or 5W-40 depending on climate). Use a quality oil filter. Check turbo inlet and charge pipes for oil seepage at every oil change.

Comparing the GTS707 to Other Turbo Kits

Several other turbo kits compete with the HKS GTS707 for K-series applications. Understanding the differences helps in making an informed decision:

Kit	Turbo	Typical Power Range	Spool (K24)	Price Range
HKS GTS707	Ball-bearing 707	300-430 WHP	~3,500 RPM	$3,500-$4,500
Garrett G30-770 (various kits)	Ball-bearing G30-770	350-480 WHP	~3,600 RPM	$3,000-$4,200
Precision 5858 (various kits)	Journal bearing 5858	350-500 WHP	~3,700 RPM	$2,500-$3,800
Full-Race BorgWarner EFR 6758	Ball-bearing EFR	320-430 WHP	~3,400 RPM	$4,000-$5,500

The HKS GTS707 occupies a sweet spot between spool response and top-end power. It does not make the highest peak power of the group, but it offers exceptional transient response and is one of the most complete, bolt-on-friendly kits available. The cast manifold and included wastegate actuation system reduce the number of potential failure points compared to kits with tubular manifolds and external wastegates. For a street-driven car that sees occasional track days, the GTS707 is a compelling choice.

The Bottom Line

The HKS GTS707 turbo kit is a mature, well-engineered product that delivers real-world power gains that are consistent with manufacturer claims. On a stock K20, expect a gain of 150-170 wheel horsepower at conservative boost levels. On a stock K24, the gain is closer to 170-200 wheel horsepower. With a built engine, the GTS707 can support up to approximately 430 wheel horsepower before the turbo becomes the limiting factor. These power levels transform a naturally aspirated Honda into a genuinely fast car that can embarrass many V8-powered vehicles on the street and the road course.

For students and educators in automotive performance programs, the GTS707 kit serves as an excellent case study in how thoughtful engineering can maximize the potential of an existing engine platform. The kit does not rely on extreme boost pressures or exotic fuels to produce impressive numbers. Instead, it leverages efficient turbocharger design, proper exhaust and intake flow, and comprehensive system integration. Understanding these principles is far more valuable than memorizing peak horsepower figures.

Whether you are building a project car for hands-on learning, preparing a vehicle for competition, or simply seeking the satisfaction of a well-tuned turbocharged Honda, the HKS GTS707 kit offers a proven path to reliable, repeatable performance gains on the K-series platform.