Shopping Cart
Sub Total:
$0
Total:
$0
You have felt the plateau. The whoosh and pull of your VF-series or mid-sized aftermarket turbo were once intoxicating, but now you crave more. The tachometer needle climbs, but the thrust you remember has faded into familiarity. You are not just a Subaru driver; you are a builder, a tuner, an enthusiast pushing the boundaries of the iconic EJ257 and EJ255. Your journey has led you here, to the threshold of high-horsepower territory, where the Precision Turbo PT6870 Subaru conversion is a well-trodden path to power. This is not a simple bolt-on. It is a statement. On a fully built engine, the Precision Gen 2 PT6870 is capable of producing over 700 wheel horsepower, a figure that transforms your street, strip, or track machine into a force to be reckoned with.
The Precision Turbo Gen 2 PT6870 is not an incremental upgrade. It is a paradigm shift. This turbocharger belongs to the "large frame" category, a significant step up in physical size and airflow capacity from the turbos that come standard on even heavily modified WRX and STI models. The "6870" designation refers to the compressor inducer size in millimeters (68mm) and the turbine exducer (70mm), placing it squarely in the power band for serious enthusiasts. The "Gen 2" represents a series of refinements over the original model, including an upgraded compressor wheel design and enhanced bearing system options, all aimed at improving response and overall durability. For the Subaru community, this turbo is a benchmark, a unit selected when the goal is to reliably break the 500-600 wheel horsepower barrier and push towards the 700+ WHP ceiling.
Understanding the specs of the Precision Turbo PT6870 Subaru build is crucial to understanding its behavior. This is not magic; it is mechanical engineering.
A central question for this turbo is: Is the Precision PT6870 a ball bearing or journal bearing turbo? The answer is that Precision offers both. The 6870 journal bearing variant is the more cost-effective option. It provides excellent performance and robust power potential. The Precision Turbo ball bearing version, however, is the king of response. The ball bearing core significantly reduces rotational friction, which translates to quicker spool times—often by several hundred RPM. For a street-driven car where transient response is key, the ball bearing upgrade is a worthy investment, though it comes at a higher initial cost.
This is the section that gets the heart racing. What can you actually expect from a Precision 6870 Subaru STI build? The numbers are impressive, but they come with a specific powerband character.
What horsepower can a PT6870 make on a Subaru STI? The power output is entirely dependent on the supporting modifications and fuel.
What is the spool time like for a PT6870 on a 2.5L Subaru? This is the most common concern. On a Subaru EJ257 2.5L block, expect full boost (typically 25-30 psi) to arrive between 4200-5000 RPM, depending on the bearing type, header design, and tuning. Below 4000 RPM, the car will feel relatively tame. But once the boost hits, it delivers a sledgehammer-like push to the redline that smaller turbos cannot match. This characteristic makes it exceptional for highway pulls, roll racing, and the drag strip, but it does require a commitment to keeping the engine in its powerband during spirited driving.
Real-world PT6870 turbo dyno results consistently show this powerband. A graph will display a torque curve that rockets up after 4000 RPM and holds power flat well past 7000 RPM. This is the signature of a properly tuned Subaru big turbo upgrade.
| RPM Range | Expected Behavior |
|---|---|
| Idle - 3800 RPM | Mild, naturally aspirated-like feel. Easy for cruising. |
| 3800 - 4500 RPM | Boost begins building rapidly. The "switch" is flipped. |
| 4500 - 7500 RPM | Peak boost and power. A relentless, linear pull to redline. |
Attempting to install a PT6870 turbo kit on a stock Subaru is a recipe for a very short-lived, and very expensive, fireworks display. The factory components are simply not designed to handle this level of airflow and power. A successful build requires a comprehensive and methodical approach.
Should I build my Subaru engine before installing a PT6870? The answer is an unequivocal yes. The factory EJ257 hypereutectic pistons are the weak link and will fail under the cylinder pressures required to make this turbo sing. A built short block is non-negotiable.
The factory fuel system is hopelessly inadequate. To feed the Precision Turbo EJ257 beast, you need a firehose, not a garden sprinkler.
What size injectors and fuel pump do I need for a PT6870 setup?
The STI's 6-speed (6MT) is robust, but at these power levels, it is being pushed to its limit. The 5-speed in older WRXs will not survive. An upgraded clutch, like the ACT Xtreme Duty Kit, is absolutely mandatory. For the 6MT, many builders opt for stronger aftermarket gear sets or dog-boxes for ultimate durability, especially for drag racing with sticky tires. The factory rear differential (R180) is generally strong enough, but axles can become a point of failure.
A Subaru big turbo upgrade generates immense heat. A high-performance aluminum radiator and a larger intercooler (front-mount is standard for this turbo size) are critical to prevent heat soak and detonation. The factory exhaust manifold is a restriction; equal-length headers are strongly recommended to improve spool and top-end flow. A full 3-inch turbo-back exhaust is the minimum requirement.
Do I need a rotated turbo kit to install a PT6870 on my Subaru? Yes, absolutely. The physical size of the Precision Turbo PT6870 and its associated inlet and downpipe flanges make it impossible to fit in the stock turbo location. A Subaru rotated turbo kit relocates the turbo to a position where the intake points towards the front of the car and the downpipe has a more direct path. This requires a new up-pipe, downpipe, intake, and often an intercooler kit. This is a complex installation best left to experienced shops or highly skilled home builders.
Is the PT6870 too big for a daily driven Subaru WRX? The answer depends entirely on your tolerance for lag and your driving style.
How does the Precision 6870 stack up against other giants in the arena?
Precision PT6870 vs. BorgWarner EFR 8374: Which is better for a Subaru? This is a classic debate. The Precision 6870 vs BorgWarner comparison often boils down to technology versus value. The BorgWarner EFR series comes with an integrated titanium aluminide turbine wheel and a gamma-Ti compressor wheel, making it incredibly responsive and technologically advanced. It often spools quicker than a comparable PT6870. However, the EFR platform is typically more expensive. The Precision Turbo Gen 2 PT6870 offers a slightly larger compressor and can often make more peak power for a lower cost, though potentially with slightly slower spool. Both are exceptional choices.
The Garrett G30-900 is another modern, ball-bearing turbo competitor. It uses Garrett's latest aerodynamic technology to provide a wide power band. The G30-900 can often spool similarly to or slightly better than a PT6870 while supporting similar or higher peak power. The choice here may come down to tuner preference, kit availability, and specific powerband goals.
| Turbo Model | Key Feature | Spool Characteristic | Peak Power Potential |
|---|---|---|---|
| Precision PT6870 Gen 2 (BB) | Proven, high-power platform | ~4300-4700 RPM | 700-750+ WHP |
| BorgWarner EFR 8374 | Integrated BOV/WG, advanced wheels | ~4000-4500 RPM | 650-700+ WHP |
| Garrett G30-900 | Modern aerodynamics, compact design | ~4200-4600 RPM | 700-800+ WHP |
The Precision Gen 2 PT6870 features an upgraded "Gen 2" billet compressor wheel designed for improved efficiency and airflow. The bearing system was also refined across the board for better durability and response compared to the original models.
The Precision PT6870 is capable of sustaining boost levels of 30-35+ psi efficiently. The real limiting factor is almost always the engine's ability to handle the resulting cylinder pressures and heat, not the turbo itself.
With a full supporting build, sticky tires, and a good driver, a PT6870-equipped Subaru is capable of deep 10-second quarter-mile passes. Traction and driver skill are the primary variables once the power is available.
Yes, it is an excellent choice. The high knock resistance of E85 allows tuners to fully exploit the turbo's airflow potential, making the Precision PT6870 and E85 a legendary combination for achieving reliable 600-700 WHP.
The Precision Turbo PT6870 Subaru project is a commitment. It is a path chosen by those who have outgrown the conventional and seek to build a truly elite, high-horsepower machine. It rewards a comprehensive, no-compromise approach to building. The sensation of the turbo coming on boost is a visceral, unforgettable experience that justifies the cost and effort for those who desire ultimate power.
If you are ready to embark on this journey, start by sourcing a quality built short block and acquiring the necessary Subaru rotated turbo kit. Partner with a tuner who has proven experience with large-frame turbos on Subaru platforms. The team at Genuine Subie Parts is here to support your build with essential components, from engine internals to cooling systems.
Ready to unleash the full potential of your EJ? Explore the Precision Turbo Gen 2 PT6870 and begin planning your ultimate Subaru build today.
Recent Comment
Be the first to comment