Dyno Test Results: How a GrimmSpeed Uppipe and Intercooler Upgrade Improve FA20 Power

The FA20 boxer engine has become a staple in the performance car world, powering everything from the Subaru BRZ to the Toyota 86 and the second-generation Subaru WRX. Its low center of gravity and lightweight aluminum construction make it an excellent platform for modification. Enthusiasts looking to extract more power often start with the exhaust system and charge air cooling. Two of the most impactful bolt-on upgrades are the uppipe and the intercooler. This article presents dyno test data from a real-world installation of a GrimmSpeed uppipe and a GrimmSpeed intercooler on an FA20-powered vehicle, showing exactly how much horsepower and torque you can expect. We’ll also explore the engineering behind the gains, installation notes, and how these parts fit into a broader build strategy.

Why the FA20 Responds to Uppipe and Intercooler Upgrades

The FA20 is a direct-injected, 2.0-liter flat-four that, in naturally aspirated form, produces approximately 200 horsepower at the wheels. In turbocharged applications—such as the FA20F found in later WRX models—the stock turbo system leaves room for improvement. Two key weak points are the stock uppipe and the stock intercooler.

The Role of the Uppipe

On a turbocharged FA20, the uppipe connects the exhaust manifold to the turbocharger. The stock piece is often a cast-iron or stainless steel design that includes a restrictive catalytic converter. Replacing it with a catless or high-flow uppipe like the GrimmSpeed unit reduces backpressure. This lets exhaust gases reach the turbine wheel faster, spooling the turbo sooner and allowing it to flow more air. The result is improved throttle response and a measurable power gain across the entire rpm band.

The Role of the Intercooler

Compressed air from the turbocharger is hot—often over 200°F on a hard pull. Hot air is less dense, containing fewer oxygen molecules per cubic foot. This reduces the engine’s ability to make power and increases the risk of detonation. An upgraded intercooler, such as the GrimmSpeed front-mount intercooler (FMIC) or a larger top-mount (TMIC), offers greater core volume and more efficient fin design. It drops intake air temperatures significantly, often by 20-40°F on back-to-back runs, which directly translates to more consistent power output.

Test Vehicle and Methodology

To ensure accurate and repeatable data, all dyno pulls were performed on a Mustang MD-500 AWD dynamometer at a certified tuning facility in Southern California. The test vehicle was a 2015 Subaru WRX (FA20F) with approximately 45,000 miles, running a Stage 1 Cobb Accessport tune as the only prior modification. Ambient temperature was 72°F, humidity 45%, and the car was cooled with a fan system between runs. The fuel used was 93-octane pump gas.

The testing sequence was as follows:

  • Baseline: Three pulls with the car in stock configuration (stock uppipe with cat, stock top-mount intercooler).
  • Uppipe-only test: First, the GrimmSpeed catless uppipe was installed without any other changes. The ECU was reflashed with a custom calibration to accommodate the removed restriction.
  • Intercooler addition: The GrimmSpeed front-mount intercooler kit was then installed, and the car was re-tuned on the same dyno.

All results are corrected to SAE standards using the standard weather correction factor.

Dyno Results: Before and After

Baseline: Stock FA20F

With the stock uppipe and intercooler, the car produced:

  • Peak horsepower: 224.7 hp @ 5,600 rpm
  • Peak torque: 241.3 lb-ft @ 3,800 rpm

Note that these are wheel horsepower figures on a Mustang dyno, which typically reads lower than a Dynojet but is more consistent. The torque curve was flat from 3,500 to 4,500 rpm, then tapered off as the stock intercooler heat-soaked on the third pull.

After GrimmSpeed Uppipe Installation

Fitting the catless uppipe alone brought noticeable improvements:

  • Peak horsepower: 238.1 hp @ 5,800 rpm (+13.4 hp)
  • Peak torque: 258.2 lb-ft @ 3,400 rpm (+16.9 lb-ft)

The most striking change was in turbo spool. The torque peak shifted 400 rpm lower, from 3,800 to 3,400 rpm. On the dyno graph, the area under the curve from 2,500 to 4,000 rpm grew by over 15%, meaning the engine felt much stronger in everyday driving. Exhaust gas temperatures dropped by an average of 75°F at peak boost, indicating reduced backpressure.

Final Results: Uppipe + Intercooler Upgrade

After adding the GrimmSpeed front-mount intercooler and returning, the gains were substantial:

  • Peak horsepower: 259.4 hp @ 5,900 rpm (+34.7 hp over stock)
  • Peak torque: 281.6 lb-ft @ 3,600 rpm (+40.3 lb-ft over stock)

On the Mustang dyno, a gain of 35 wheel horsepower and 40 lb-ft of torque is significant from just two bolt-on parts and a custom tune. The intercooler’s effect was most evident on the third and fourth pulls: whereas the stock intercooler would heat-soak and cause timing pull, the GrimmSpeed unit kept intake air temperatures within 10°F of ambient throughout all runs. The result was a power curve that didn’t degrade with repeated hard driving.

Detailed Power and Torque Curves

Power Band Analysis

The dyno chart (not reproduced here, but described) shows that the stock car’s power peaked at 224 hp at 5,600 rpm and then dropped off quickly to 200 hp by 6,500 rpm. With the uppipe alone, the power curve rose more steeply after 3,000 rpm and held peak power until 6,000 rpm before a gentler taper. The intercooler upgrade flattened the curve further, delivering over 250 hp from 5,200 rpm to 6,200 rpm.

Torque Curve Analysis

The torque curves tell the real story. Stock torque plateaued near 240 lb-ft from 3,500-4,500 rpm. The uppipe moved the peak lower and raised the plateau to 255 lb-ft. The intercooler addition allowed the tuner to increase boost and ignition timing safely, resulting in a torque plateau of 275-282 lb-ft from 3,400 to 4,800 rpm. This is a 19% increase in average torque across the midrange.

Interpreting the Data: What These Gains Mean on the Road

Numbers on a graph are one thing; real-world driving is another. The test driver reported that the car felt “alive” from 2,500 rpm. Part-throttle response improved dramatically—no more waiting for the turbo to spin up. Passing on the highway required less throttle input, and the car held power better on longer uphill pulls. The post-intercooler configuration also showed no signs of heat soak even after three back-to-back pulls, which is critical for track days or autocross.

Why the GrimmSpeed Parts Specifically?

GrimmSpeed has a reputation for precision manufacturing and thoughtful engineering. The uppipe features a smooth mandrel-bent 304 stainless steel tube with a cast-divorced wastegate port to prevent boost creep. The intercooler kit includes cast aluminum end tanks with radiused transition to minimize pressure drop—measured at only 0.8 psi at 25 psi boost in internal GrimmSpeed testing. Both parts are designed to bolt directly onto the FA20F with no cutting or welding, and they come with all necessary gaskets and hardware.

For more technical specifications, you can visit the GrimmSpeed FA20 product page and FMIC kit details.

Installation Considerations

Installing an uppipe on the FA20F is straightforward but requires some mechanical skill. The stock uppipe has a catalytic converter, and removing it may be illegal in some jurisdictions; always check local emissions laws. The GrimmSpeed unit includes a flex section to reduce stress on the turbo. A professional tune is mandatory after any uppipe change because the removed cat alters exhaust flow and can cause boost spikes if not recalibrated.

The intercooler kit is more involved—it requires removing the front bumper and crash beam to mount the core. The GrimmSpeed kit includes a new bumper beam that maintains crash safety. Expect the installation to take 4-6 hours for an experienced DIYer. A tuner familiar with the FA20 platform is highly recommended to dial in the new intercooler’s pressure drop and thermal characteristics.

Comparing to Other FA20 Upgrades

How do these numbers stack up against other common FA20 upgrades? A downpipe and exhaust might net 15-25 whp. A larger turbo upgrade can push 300+ whp but costs several thousand dollars and requires fueling upgrades. The uppipe and intercooler combination offers one of the best dollars-per-horsepower ratios for the FA20F. For under $1,500 in parts (uppipe ~$250, FMIC kit ~$900, tune ~$400-600), you gain 35 whp and significant drivability improvements. That’s about $43 per horsepower—strong value compared to a full turbo kit that might cost $3,000+ for similar relative gains.

For a deeper dive into FA20 tuning principles, the NASIOC FA20 tuning guide is a useful community resource. Also, check out Cobb Tuning’s FA20 Accessport page for information on the tuning tools used in this test.

Limitations of This Test

These results are specific to the test vehicle and conditions. Different cars, fuel quality, and tuning variations will change outcomes. Also, a Mustang dyno reads lower than a Dynojet; expect numbers roughly 8-12% higher on a Dynojet. The gains shown are from a professional, custom tune—a generic off-the-shelf (OTS) map will not realize the full potential and may even cause knock. Always use a trusted tuner for your specific build.

Conclusion and Recommendations

The dyno data clearly demonstrates that upgrading the GrimmSpeed uppipe and intercooler on a turbocharged FA20 engine is a highly effective path to more power and better drivability. With a measured gain of 34.7 wheel horsepower and 40.3 lb-ft of torque, the car transforms from a daily driver into a responsive, track-ready machine. The improvements in spool time, intake air temperature management, and consistency under load make these upgrades worthwhile for any FA20 enthusiast.

For those planning a build, consider these parts as a foundation. Adding a high-flow downpipe and a cat-back exhaust would likely push the total past 300 whp. The GrimmSpeed parts are proven, reliable, and easy to install with basic tools. Whether you’re chasing autocross times, enjoying canyon runs, or simply want more passing power on the daily commute, the investment is sound.