The Path to 450+ Horsepower: Intercooler and Turbo Upgrades for Your WRX E85 Conversion

The Subaru WRX is a platform that thrives on modification. For owners seeking serious power, running E85 fuel has become a proven path to four-digit crank horsepower numbers. But hitting the 450+ wheel horsepower mark requires more than just a flex-fuel kit and a tune. The intercooler and turbocharger systems need to be completely rethought. This guide covers the best intercooler and turbo upgrades for a WRX E85 conversion, including supporting modifications, component choices, and real-world considerations to help you build a reliable, high-output street machine.

Why E85 Fuel Is a Game-Changer for the WRX

E85, a blend of 85% ethanol and 15% gasoline, offers distinct advantages over pump gas when targeting 450+ wheel horsepower. Ethanol has a latent heat of vaporization roughly three times higher than gasoline, which means it absorbs more heat from the intake charge as it evaporates. This cooling effect reduces intake air temperatures (IATs) and suppresses detonation, allowing tuners to run higher boost pressures and more aggressive ignition timing.

E85 also carries a high octane rating—typically around 105 to 110 research octane number (RON)—which directly increases knock resistance. This is critical for small-displacement forced-induction engines like the WRX’s EJ25 or FA20. The trade-offs include roughly 25% worse fuel economy and the need for a much larger fuel system because the engine requires about 30% more fuel volume per power stroke. Availability varies by region, so always check local stations before committing to a full conversion.

For a reliable 450+ whp setup, the factory intercooler and turbocharger will quickly become bottlenecks. Upgrading both components is essential to maintain safe IATs and deliver the airflow required by the added ethanol.

Intercooler Upgrades: Keeping Charge Air Cool

A stock WRX top-mount intercooler (TMIC) can start heat-soaking after just one or two hard pulls on pump gas. On E85, where the engine can make much more heat, an efficient intercooler becomes even more critical. IATs must stay below 130°F at peak boost to avoid knock on the street. Two main paths exist: a high-flow top-mount or a front-mount intercooler (FMIC).

Top-Mount vs. Front-Mount

TMICs retain the factory routing, shorter piping, and lower pressure drop, which helps turbo spool. They work well for street cars that see moderate boost levels and occasional track use. However, even the best TMIC can struggle to keep IATs in check during back-to-back pulls in hot weather.

FMICs offer a much larger cooling surface area and sit in direct airflow behind the bumper. The downside is longer charge piping, which adds slight turbo lag and requires cutting the bumper beam or crash bar on some models. For a 450+ whp goal on E85, an FMIC is often the better choice for sustained performance.

Top Intercooler Options for 450+ HP

  • Process West Verticooler: This bar-and-plate top-mount design uses a vertical core orientation to maximize airflow through the hood scoop. The Verticooler has a core volume roughly 30% larger than stock and is one of the few TMICs that can support 450+ whp on E85 without excessive heat soak. It includes a redesigned splitter and gasket kit for a direct fit on 2015+ WRX and STI models. Process West backs it with dyno-proven results.
  • GrimmSpeed Front-Mount Intercooler Kit: GrimmSpeed’s FMIC system includes a 3-inch core with cast end tanks and mandrel-bent piping. It drops IATs by up to 30°F compared to a stock TMIC on the same boost levels. The kit includes a robust mounting bracket system and a high-tension couplers to prevent boost leaks. This unit is a go-to for many Subaru shops building 400-500 whp street cars.
  • Cobb Tuning Front-Mount Intercooler: Cobb’s FMIC is engineered for durability and flow consistency. The core uses staggered internal fins to maximize heat rejection while minimizing pressure drop. It supports up to 650 whp, providing plenty of headroom for future upgrades. The kit comes pre-assembled with high-quality silicone hoses and T-bolt clamps.

For builds strictly targeting 450-500 whp on E85, either of these FMICs will work well. The GrimmSpeed and Cobb units are nearly interchangeable in performance; choose based on budget and fitment preference. If you prefer to keep the engine bay clean and stick with a TMIC, the Process West Verticooler is the only TMIC that can truly handle that power level in hot conditions.

Turbocharger Upgrades: Choking the Airflow? Not Anymore

The stock WRX turbocharger (typically a TD04 on earlier models, an MHI TD05 on 2002-2007 STIs, or the smaller twin-scroll unit on 2015+ WRX) maxes out around 300-350 whp on pump gas. On E85, the added fuel flow can push that slightly higher, but you will quickly run out of compressor flow. To reach 450+ whp, you need a turbo that can flow around 50-55 lb/min of air at a boost pressure around 22-26 psi.

Three popular options fall into that flow range while still offering reasonable spool characteristics for a street car.

Option 1: Garrett GT2871R (GTX2867R Gen II)

The Garrett GT2871R with a 0.64 A/R turbine housing has been a Subaru staple for decades. Its modern counterpart, the Garrett GTX2867R Gen II, uses an advanced billet compressor wheel and dual-ball-bearing center cartridge. On E85, this turbo can produce 450-480 whp with full boost by 3600-3800 rpm. Spool is excellent, making it ideal for autocross, canyon carving, or daily driving. Garrett Motion offers tuneable options for various engine displacements.

Option 2: Blouch 20G XT

Blouch Performance builds custom turbos specifically for Subaru applications. The 20G XT uses a TD06h 20G compressor wheel (a proven high-flow design) paired with a billet turbine wheel and a modified ported shroud compressor housing. It flows approximately 49-52 lb/min, enough for 450-480 whp on E85. Spool is a touch later than the GTX2867R—full boost around 3800-4000 rpm—but peak power potential is slightly higher. Reliability is exceptional thanks to triple-thrust bearing technology and oversize oil passages.

Option 3: FP Green (Force Performance Green)

The FP Green series uses a Garrett GT30R-based compressor wheel with a TD06 turbine. It is a larger unit than the 20G, flowing up to 55 lb/min. On E85, an FP Green can push 500+ whp with the right supporting mods, but it comes with a tradeoff in spool: full boost arrives around 4200 rpm. This makes it a better choice for drag racing or roll racing where you stay in higher rpm ranges. For a street-driven 450+ whp build, the FP Green offers a beautiful balance of power and port fuel injector compatibility.

All three turbos require an upgraded fuel system and proper tuning. The Garrett and Blouch units spool quickly enough to remain enjoyable on the street, while the FP Green demands a bit more rpm but rewards with top-end rush. If you want quick spool and 450 whp, go with the GTX2867R. If you plan to push past 500 whp later, the FP Green gives you room to grow.

Supporting Modifications: The Unsung Heroes

Installing a big intercooler and turbo on your WRX without upgrading the fuel system, exhaust, and tune is a recipe for detonation and mechanical failure. Here are the essential supporting mods for a successful 450+ whp E85 build.

Fuel System Upgrades

E85 requires roughly 30% more fuel volume than pump gas. The stock injectors and fuel pump cannot keep up. You need:

  • High-flow fuel injectors: At least 1000 cc/min for 450 whp on E85; 1300-1600 cc/min is safer. Brands like Injector Dynamics, Bosch, or DeatschWerks are common choices.
  • In-tank fuel pump: A Walbro 255 lph pump is barely enough; a 340-450 lph pump (AEM, DW400) is strongly recommended. For extra safety, consider a dual-pump setup or a surge tank/brushless pump.
  • Fuel pressure regulator: Adjustable return-style regulators (Aeromotive, Fuelab) allow precise tuning of fuel pressure to match the injectors and pump curves.
  • Fuel lines: Upgrade the feed line from the tank to the engine bay to -6AN or -8AN to handle the flow. The stock hard lines can be a restriction.

ECU Tuning

A custom tune on a standalone ECU (Haltech, Link, Motec) or a reflash tool (Cobb Accessport, EcuTek) is mandatory. Do not run a generic “flex-fuel” base map for 450 whp. The tuner will adjust fuel tables, ignition timing, boost control, and MAF scaling specifically for your hardware and fuel. A professional dyno tune is the safest path; many Cobb Tuning Pro Tips recommend starting conservative and refining over several pulls.

Exhaust System

The stock exhaust system (especially the downpipe and catalytic converter) chokes airflow. A 3-inch turbo-back exhaust with a high-flow catalytic converter is essential for 450+ whp. The removal of the catalytic converters on a catless downpipe will increase flow but also increase noise and may fail emissions inspections. Choose a stainless steel system from Invidia, Cobb, or Greddy for proven results.

Intake and Charge Pipe

The factory intake box is restrictive at high boost. A cold-air intake (CAI) with a large filter element and a smooth MAF housing will help spool and prevent measured turbulence. Pair it with an upgraded metal charge pipe that eliminates the plastic factory pipe prone to blowing off couplers.

Engine Internals

For 450 whp on E85, the stock Subaru EJ257 or FA20 closed-deck block can handle it with proper tuning and bolt-ons. However, many builders upgrade the pistons and rods (Manley, CP-Carrillo) for safety, especially if you plan to track the car or run high boost frequently. At this power level, a well-maintained stock bottom end can survive for years on a conservative tune. If you ever plan to exceed 500 whp, forged internals become a necessity.

Sample 450+ WHP Build: Parts List and Estimated Costs

Here is a realistic parts list for a Subaru WRX (2008-2014 STI or 2015+ WRX) targeting 460 whp on E85:

  • Turbo: Blouch 20G XT – $1,800
  • Intercooler: GrimmSpeed FMIC – $1,200
  • Fuel Injectors: DeatschWerks 1300 cc/min – $400
  • Fuel Pump: Walbro 450 lph in-tank – $250
  • Fuel Pressure Regulator: Aeromotive return-style kit – $300
  • ECU Tune: Cobb Accessport plus dyno tune – $1,500
  • Exhaust: Invidia Catless Downpipe + catback – $1,100
  • Intake: Cobb SF Intake + Box – $350
  • Miscellaneous: Clamps, hoses, gaskets – $500

Total estimated cost: $7,400 plus labor. This budget assumes you have a healthy engine and you are doing the install yourself. If you pay a shop, add $2,000-3,000 for labor and tuning. The result will be a street car that can run 11-second quarter-mile times, pull hard from 3,500 rpm to redline, and stay reliable on E85 as long as you keep the fuel system clean and the tune conservative.

Conclusion

Reaching 450+ wheel horsepower on a WRX using E85 is an achievable goal with the right intercooler and turbo upgrades. Choose a front-mount intercooler like the GrimmSpeed or Cobb units to keep IATs in check, and pair it with a turbocharger that matches your rpm preference—the Garrett GT2871R for quick spool, the Blouch 20G XT for proven reliability, or the FP Green for top-end power. Do not skimp on supporting modifications: a proper fuel system, a professional tune, and a free-flowing exhaust are non-negotiable. With careful planning and a solid budget, your WRX can become a 450+ whp E85 monster that turns heads at every stoplight.