The Subaru Forester may be known as a practical family SUV, but with the right turbo modifications, it transforms into a serious performance machine capable of exceeding 250 horsepower at the wheels. Whether you own an SG, SH, SJ, or SK generation, the engine bay offers plenty of room for upgrades. In this guide, we break down the best turbocharger sizes, supporting modifications, and trusted brands to help you build a reliable 250+ whp Forester.

Understanding the Forester Turbo Platform

Most Forester XTs from 2004 onward use Subaru’s turbocharged EJ20, EJ25, or later FA20DIT engines. These engines come with forged or cast internals depending on the year and market, but even the stronger EJ255 and EJ257 blocks have limits. Stock turbochargers like the TD04 or VF52 top out around 230–260 whp with supporting mods and tune. To reliably hit 250+ whp, you need a larger turbo, upgraded fueling, and better engine management. Understanding your engine’s strengths and weaknesses is key before selecting components.

Choosing the Right Turbocharger: Size Matters

Turbo selection is the most important decision for a 250+ whp build. The goal is to match the turbo’s flow capacity with your target power while maintaining quick spool for daily drivability. For a Forester, a turbo in the 49–57 lb/min range is ideal. Key terms to know:

  • Compressor trim – affects airflow and efficiency.
  • Turbine A/R – controls spool speed and backpressure.
  • Wheel technology – billet wheels like Garrett’s GTX or Blouch’s XT series reduce lag.

Recommended turbo sizes for 250–350 whp: Garrett GTX2867R (52 lb/min, quick spool), Blouch 20G-XT (49 lb/min, great street torque), Precision 5858 (58 lb/min, more top-end). Avoid oversized units like 6266 unless you accept lag and need 400+ whp.

Top Turbocharger Kits and Sizes for 250+ HP

Garrett GTX2867R

The GTX2867R is a favorite for Subaru street builds. Its 48mm compressor wheel flows enough for 350 whp while spooling like a stock turbo. With an .86 A/R turbine housing, it reaches full boost by 3200–3500 rpm on a 2.5L. Ideal for daily-driven Foresters wanting instant response and headroom for future upgrades. A full kit from Garrett Motion includes water and oil lines.

Blouch 20G-XT

Blouch Turbo’s 20G-XT uses a billet compressor wheel and a ported shroud for better flow. It delivers 49 lb/min, supporting 300–340 whp with a conservative tune. The 10cm² turbine housing keeps exhaust velocity high, making it a direct bolt-on for many Forester XTs. Blouch also offers custom rebuilds and performance upgrades specific to Subaru. See their Blouch Turbo lineup.

Precision Turbo 5858 Gen2

For those planning to push toward 400 whp, the Precision 5858 Gen2 is a ball-bearing turbo with a 58mm compressor wheel. It flows 65 lb/min but can be run safely at 280–350 whp with conservative boost. Requires upgraded fuel system and intercooler. Precision offers a Subaru-specific T3 flange kit.

HKS GTIII-5R

HKS’s GTIII-5R is a high-end ball-bearing turbo with a unique turbine housing design for reduced lag. Rated at 320 whp, it uses a stainless steel turbine housing and a 5cm² throat for fast spool. Pricier but known for reliability. HKS also provides tuning software and supporting gear.

Turbo ModelFlow (lb/min)Max WHP (estimated)Spool (2.5L)Price Range
Garrett GTX2867R52350~3300 rpm$1300–$1600
Blouch 20G-XT49340~3400 rpm$1100–$1400
Precision 5858 Gen265400~3800 rpm$1500–$1800
HKS GTIII-5R52320~3200 rpm$1800–$2200

Supporting Mods: Intercooler, Exhaust, and Intake

A larger turbo requires more airflow and cooler intake temperatures. Without these supporting mods, even the best turbo will heat-soak or fail to reach full potential.

Intercooler Upgrades

Stock top-mount intercoolers (TMIC) quickly become heat-soaked above 15 psi. Two options: an upgraded TMIC like the Process West Verticooler or a front-mount intercooler (FMIC) kit from COBB Tuning. The Verticooler flows 30% more and fits under the stock hood. COBB’s FMIC offers lower pressure drop and consistent IATs but requires cutting bumper beam. Also consider Grimmspeed TMIC for a mid-range option with great core quality.

Exhaust System

To reduce backpressure and help the turbo spool, upgrade the entire exhaust from the downpipe back. A 3-inch downpipe with high-flow cat is essential. Pair it with a cat-back exhaust: the Invidia Q300 offers aggressive tone without drone. Nameless Performance allows custom muffler options. For maximum flow, HKS Hi-Power uses straight-through design. Headers (equal-length or unequal-length) further improve exhaust scavenging but are not necessary at 250 whp.

Cold Air Intake

A larger intake like the COBB SF Intake or Process West CAI reduces restriction and can be tuned for higher airflow. Stick to known brands to avoid MAF scaling issues.

ECU Tuning and Fuel System

No turbo upgrade works without proper engine management. The Subaru ECU can be tuned via COBB Accessport (easy OBD-II flashing), ECUtek (pro-tune for custom maps), or open-source like RomRaider. A protune is highly recommended for a 250+ whp build to dial in timing, boost, and fuel.

Fuel System Upgrades

At 250–350 whp, you need larger injectors (typically 750–1000 cc/min) and a high-flow fuel pump like the DW300c or AEM 340LPH. For those chasing 300+ whp, consider a Flex Fuel kit to run ethanol (E50–E85) for extra octane and cooling. Cobb Flex Fuel or Delicious Tuning Flex Fuel are popular. A fuel pressure regulator may be needed if pump volume exceeds stock regulator capacity.

Internal Engine Upgrades for 250+ HP Reliability

While many Forester engines survive 250 whp on a good tune, reliability improves with forged internals. Consider:

  • Forged pistons (e.g., CP-Carrillo, Wiseco) for higher boost tolerance.
  • H-beam connecting rods (Manley, Eagle) to handle torque spikes.
  • ARP head studs to prevent head lift at elevated cylinder pressures.
  • Oil pickup tube upgrade (Killer B Motorsport) to prevent starvation.
  • AOS/CCV system (IAG, Crawford) to reduce blow-by and improve PCV health.

If your Forester has high miles (>100k), baseline compression and leak-down tests are wise before adding power.

Budget and Build Planning

Building a 250+ whp Forester can cost $3,000–$6,000 for a basic parts list including turbo, intercooler, exhaust, injectors, pump, and tune. Labor adds another $1,500–$3,000 if you’re not DIY. For a full forged motor build, expect $6,000–$10,000. Plan your goals first: do you want a quick daily driver (250 whp), an autocross weapon (300 whp), or a drag weekend car (350+)? Each tier demands different components.

A popular “stage 2+ turbo” package for 280 whp: Blouch 20G-XT, Grimmspeed TMIC, Cobb downpipe + cat-back, DW300 pump, 850cc injectors, Cobb Accessport with protune. This setup is reliable, retains AC and power steering, and drives like stock until you hit boost.

Conclusion

Achieving 250+ horsepower in your Subaru Forester is not a fantasy — it’s a well-documented path with proven turbo kits, intercoolers, fuel systems, and tuning solutions. Choose a turbo sized for your power target and driving style, support it with a quality intercooler and exhaust, and never skip a professional tune. With a balanced approach, your Forester will confidently deliver SUV practicality alongside genuine sport-compact performance. Whether you daily it or compete at track days, these mods unlock the potential Subaru engineered into the chassis.