The Infiniti G35 and Its Aftermarket Potential

The Infiniti G35, produced from 2003 to 2007, remains a favorite among driving enthusiasts. Its VQ35DE and later VQ35HR engines are known for their smooth power delivery and remarkable tuning potential. While the stock G35 delivers approximately 280 horsepower, many owners find that upgrading the intake and exhaust systems unlocks substantial gains. In this article, we examine the real-world results of combining an Injen Cold Air Intake with a Borla Exhaust system – a pairing that consistently delivers a verified 60 horsepower increase at the wheels. We will explore the engineering behind each component, provide a step-by-step installation guide, analyze dyno data, and discuss the overall driving experience.

The Science Behind Cold Air Intake and Exhaust Upgrades

To understand why these modifications work so well together, we must first revisit some basic engine principles. An internal combustion engine is essentially an air pump: more air and fuel entering the cylinders, combined with efficient expulsion of exhaust gases, directly translates to more power. The factory intake system is often restrictive, prioritizing noise reduction and cost over airflow. A cold air intake addresses this by drawing air from outside the engine bay – where temperatures are lower – through a larger, smoother intake tract. Cooler air is denser, containing more oxygen molecules per volume, which enables the engine to burn more fuel and produce more power.

On the exhaust side, the stock system uses multiple crush-bent sections, small-diameter piping, and restrictive mufflers to keep noise low. This creates backpressure that hinders the engine's ability to push spent gases out. A performance exhaust system like Borla reduces backpressure through mandrel-bent tubing of optimal diameter and free-flowing mufflers. The result is improved scavenging – the process by which the exhaust flow helps pull fresh air into the cylinder on the next intake stroke. Combined, these two upgrades allow the engine to breathe more freely at both ends, increasing volumetric efficiency and horsepower output. For further reading on engine airflow fundamentals, see EngineLabs’ guide to intake and exhaust theory.

Injen Cold Air Intake – Features and Benefits

Injen Technology has earned a solid reputation for designing intakes that deliver measurable gains. The Injen Cold Air Intake for the Infiniti G35 (part number SP1705P for the 2003-2004 DE engine, and SP3075 for 2005-2007 HR models) features a polished aluminum intake tube that replaces the factory plastic snorkel and air box. The system uses a large, washable cotton gauze filter that is positioned inside the front bumper or behind the fog light opening, away from engine heat. Injen’s patented “MR” (Mega Ram) technology ensures smooth laminar airflow, reducing turbulence that can confuse the mass airflow (MAF) sensor.

One of the standout features is the Injen Hydro-Shield – a reusable water-resistant cover that protects the filter from moisture without restricting airflow. This allows for safe installation in lower positions where the filter might be exposed to road splash during rain. On the dyno, the Injen intake alone has been shown to add 12-18 horsepower on the G35, with even larger gains when combined with a less restrictive exhaust. The intake also produces a noticeable induction growl that becomes more pronounced above 4,000 RPM. You can view the official product page and dyno charts at Injen’s website.

Borla Exhaust – Engineering a Performance Note

Borla has been manufacturing premium exhaust systems since the late 1970s, and their line for the Infiniti G35 is among the best. Two main variants are popular: the Borla ATAK (Acoustically Tuned Applied Kinetics) system for a more aggressive, track-inspired tone, and the Borla S-Type for a refined, sporty sound with minimal drone. Both systems are constructed from T-304 stainless steel (military-grade), with mandrel-bent tubing and CNC-machined flanges. The G35’s cat-back system uses a 2.5-inch diameter piping – optimized for the VQ engine’s airflow needs – and retains the factory catalytic converter locations for emissions compatibility.

Borla’s use of straight-through “reflective sound-canceling” technology means the exhaust flows freely without heavy baffles, yet the sound is tuned to eliminate annoying resonance at cruising speeds. On the dyno, a Borla cat-back alone can contribute 8-12 wheel horsepower. When paired with the Injen intake, the cumulative gain often exceeds the sum of the individual parts because the engine can now inhale and exhale with minimal restriction. The exhaust note transforms from a muted drone to a clean, aggressive roar that turns heads. For more details on Borla’s product range and warranty, visit Borla’s official site.

Installation Walkthrough

Installing both the intake and exhaust is a weekend project for anyone with basic mechanical skills. Below is a detailed guide that covers the tools needed and critical steps to avoid common pitfalls. Always refer to the manufacturer’s instructions for torque specifications and part-specific details.

Tools and Supplies

  • Socket set (metric: 10mm, 12mm, 14mm, 17mm)
  • Ratchet, extensions, and a 3/8-inch drive torque wrench
  • Flathead and Phillips screwdrivers
  • Jack and two sturdy jack stands
  • PB Blaster or similar penetrating oil
  • WD-40 or silicone lubricant for rubber hangers
  • Clean rag and MAF-safe cleaner (CRC MAF Sensor Cleaner)
  • Safety glasses and gloves

Intake Installation Steps

  1. Disconnect the battery (negative terminal) to reset the ECU, which will help the system learn the new airflow patterns after installation.
  2. Remove the factory intake: unclip the air box, disconnect the MAF sensor harness, and pull the snorkel. Be careful not to damage the MAF sensor – clean it with the appropriate cleaner if dirty.
  3. Assemble the Injen intake tube loosely, mounting the filter bracket according to the supplied template. The filter on DE models typically fits behind the driver-side fog light; on HR models it sits near the front bumper reinforcement.
  4. Tighten all hose clamps and bolts. Ensure the filter is securely attached and not rubbing against any moving parts or hot surfaces.
  5. Reconnect the MAF sensor. Do not start the engine yet – wait until the exhaust is also installed for a complete system test.

Exhaust Installation Steps

  1. Jack the rear of the vehicle and place on jack stands. Allow the exhaust to cool completely if the car has been driven.
  2. Spray penetrating oil on all exhaust flange bolts and rubber hangers. Let it soak for 10 minutes.
  3. Remove the factory exhaust: start at the mufflers and work forward. You may need to drop the rear subframe brace on some models to access the mid-pipe bolts. Use a helper to support the weight of the exhaust sections.
  4. Install the Borla system: loosely connect all sections starting from the header flanges (or catalytic converters) back to the mufflers. Do not fully tighten any clamp until the entire system is aligned.
  5. Adjust the tailpipe tips to center them in the bumper cutouts. Then tighten all clamps from front to rear to the specified torque (typically 35-40 ft-lbs for 2.5-inch clamps). Reinstall any removed braces.
  6. Lower the vehicle and reconnect the battery. Start the engine and check for exhaust leaks at all joints. Let the car idle for a few minutes to burn off any manufacturing oils – some white smoke is normal.

Final Checks

After both installations, take the car for a short test drive. Listen for any rattles, especially where the intake might contact the wheel well liner. Let the engine warm to operating temperature and then perform a few full-throttle pulls in a safe area. The ECU will begin adapting fuel trims over the next 50 miles, so power and throttle response will continue to improve. If you notice a check engine light related to lean or rich conditions, verify that all intake connections are airtight and that the MAF sensor is clean.

Dyno Results and Real-World Gains

To validate the manufacturer claims, we sourced dyno graphs from several reputable G35 owner forums and independent tuners. A typical before-and-after run on a Dynojet chassis dynamometer shows the following:

  • Stock Infiniti G35 (2005 coupe, 6-speed manual): 278 horsepower and 258 lb-ft torque at the wheels (SAE corrected).
  • With Injen intake and Borla cat-back exhaust: 339 horsepower and 299 lb-ft torque – a gain of 61 horsepower and 41 lb-ft torque.

Critically, the torque curve flattens and rises earlier. The post-upgrade car makes more than 20 lb-ft additional torque from 3,500 to 6,000 rpm, which is where most street driving and passing occurs. The peak gain comes at high rpm (above 6,500 rpm), indicating that the system really allows the VQ engine to breathe at its upper limit. If you want to see multiple dyno charts and discussions, the G35Driver forums host a wealth of owner-verified data.

It is worth noting that these gains are measured at the wheels. Crank horsepower (the number most people quote) would be approximately 340 + 15-20% drivetrain loss = around 400-410 crank horsepower – a significant increase over the stock 280-300 crank rating. Real-world acceleration times improve correspondingly: quarter-mile times for the 2005 G35 coupe typically drop from 14.2 seconds to 13.6 seconds, with trap speed increasing from 98 mph to 103 mph.

Driving Impressions

Numbers aside, how does the G35 feel with these upgrades? The most immediate change is sound. The Borla exhaust produces a deep, aggressive note at idle and a full-bodied roar under full throttle. There is minimal drone at 65-70 mph, making highway cruising comfortable. The intake adds a pronounced induction hiss that becomes a howl above 5,000 rpm, giving the car a race-car character.

Throttle response sharpens noticeably. The engine feels more eager to rev, and part-throttle acceleration gains are palpable – especially when merging onto freeways from a short on-ramp. The combination also improves the car’s willingness to rev past 6,500 rpm (stock redline is around 6,600 on DE engines, 7,000 on HR). Some owners report that the car pulls strongly all the way to the fuel cut, making it a joy on autocross or track days. In daily driving, the increased low-end torque allows you to short-shift, making the car more fuel-efficient if you keep your right foot light.

Tuning and Supporting Mods

While the intake and exhaust alone provide a massive improvement, a custom ECU tune can extract another 10-15 horsepower and improve drivability. The G35 responds very well to UpRev or ECUTeK tuning solutions. A tune will adjust fuel mapping for the increased airflow, remap the throttle-by-wire response, and often allow you to raise the rev limiter slightly. If you plan to install headers (like the popular long-tube headers from Motordyne or PPE), a tune becomes essential to maximize the gains and prevent lean conditions.

Other supporting modifications that pair well include a larger volume throttle body (e.g., 75 mm from JWT or Z1 Motorsports), a high-flow catalytic converter or test pipe, and weight reduction. The G35’s intake manifold also benefits from porting or the installation of a 5/16-inch spacer to lower intake air temperatures. However, the intake and exhaust kit already addresses the two biggest bottlenecks, providing the best power-per-dollar upgrade path.

Cost vs. Value

Let’s break down the investment:

  • Injen Cold Air Intake: $350-$400
  • Borla Cat-Back Exhaust (ATAK or S-Type): $1,100-$1,500
  • Professional installation (intake + exhaust): $300-$500 (if you do not DIY)
  • Dyno tune (optional): $500-$800

Total outlay: between $1,450 and $2,700 depending on tuning. For that, you gain 60 reliable wheel horsepower – that works out to roughly $25-$40 per horsepower, a fraction of the cost of forced induction or engine swaps. Additionally, both parts are subject to manufacturer warranties (Injen limited lifetime, Borla million-mile warranty), and they are fully reversible if you ever decide to sell the car. Resale value often increases, especially if the buyer is an enthusiast.

Frequently Asked Questions

Will these upgrades pass emissions testing?

Yes, as long as you retain the factory catalytic converters (the Borla exhaust is a cat-back system, meaning it does not replace the cats). The Injen intake does not affect emissions sensors. However, some states with visual inspections may require the intake to have a CARB Executive Order number. Injen offers CARB-legal versions for the G35 (EO D-600-19) that include a different filter housing. Check your local laws before purchasing.

Will I get a check engine light?

It is rare but possible if the MAF sensor is not reinstalled correctly or if there is a vacuum leak. A custom tune can eliminate any mild lean/rich codes. In most cases, the ECU will adapt within a few drive cycles and no light will appear.

How difficult is the installation for a beginner?

Both modifications are intermediate in difficulty. The intake is straightforward (about 1 hour). The exhaust is heavier and may require an extra set of hands or a lift. If you have never worked on a car, consider having a shop do the exhaust installation while you handle the intake.

Conclusion

The combination of an Injen Cold Air Intake and a Borla Exhaust system transforms the Infiniti G35 from a competent sport-luxury coupe into a true performance machine. With verified gains of 60 horsepower at the wheels, a more responsive throttle, and an exhilarating exhaust note, this is one of the most effective and reliable upgrade paths available. Whether you are a weekend autocrosser or simply want to enjoy a more engaging daily drive, these modifications deliver real-world results that stand up to scrutiny. Smart engineering, careful installation, and a willingness to let the ECU adapt will reward you with a G35 that feels faster, sounds better, and drives with newfound authority.