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Want to squeeze a little more performance—or personality—out of your Honda Acty? Upgrading the intake and exhaust system is one of the most effective and rewarding ways to improve throttle response, airflow, and even fuel efficiency. Whether you're aiming for a bit more grunt, a better tone, or just a cleaner look under the rear hatch, this guide walks you through the best bolt-on mods for air and exhaust on your Acty.

1. Air Filter & Intake Box Upgrades

The stock airbox on the Acty is restrictive, built for noise control—not performance. Upgrading it allows the engine to breathe better, especially at higher RPMs.

Options for better airflow:

• Drop-in performance filter (OEM airbox):

  • Brands like K&N or HKS offer washable high-flow filters

  • Easy install, subtle gain in throttle response

• Cold air intake (custom or DIY):

  • Relocate filter for cooler air away from the engine

  • Use a cone-style filter with custom piping

  • Requires careful placement to avoid water intake (especially on off-road builds)

• Velocity stacks or short-ram intakes:

  • For tuned or carbureted Acty engines

  • Improved airflow, increased intake noise

🧰 Oiwa Tip: Always support aftermarket piping securely—vibration can damage thin aluminum kits.

2. Headers & Exhaust Manifolds

Factory headers are heavy, restrictive, and prone to cracking over time. Upgrading to performance headers can improve scavenging and torque.

Popular header upgrades:

• Stainless steel tubular headers:

  • Lightweight and flow more efficiently than cast iron

  • Available from specialty kei tuning brands in Japan

  • May require slight modification for downpipe alignment

• Heat-wrapping headers:

  • Reduces engine bay temps

  • Improves exhaust gas velocity for better midrange power

Note: Some models require moving the oil filter or modifying EGR tubing to fit aftermarket headers—check clearance before ordering.

3. Exhaust System: From Mild to Wild

From silent factory pipes to custom throaty systems, your exhaust setup defines your Acty’s tone and backpressure.

Upgrade tiers:

• OEM+ muffler replacement:

  • Slightly deeper tone

  • Improved flow without excess noise

  • Bolt-on axle-back options available for HA3/HA4 and HH3/HH4

• Cat-back or full exhaust system:

  • 1.5" to 2.0" mandrel-bent piping recommended

  • Less restriction, more responsive throttle

  • Custom or imported systems (Fujitsubo, Kakimoto, or local fab)

• Muffler choices:

  • Chambered mufflers = deeper tone, no drone

  • Straight-through mufflers = louder, higher pitch

  • Resonators = reduce rasp without cutting power

🔧 Pro Tip: Always check local noise regulations before going full straight-pipe—many areas have 90–95dB legal limits.

Final Thoughts

Intake and exhaust upgrades are some of the most rewarding and beginner-friendly mods you can make to your Honda Acty. You get better drivability, a sportier sound, and a touch of performance—all while keeping the kei-class charm.

At Oiwa Garage, we source bolt-on headers, filters, and exhaust kits tailored to every Acty chassis. Whether you want subtle gains or a fully custom sound, we’ll help you choose parts that fit your goals—and your truck.