The Honda D-series engine has long been a favorite among enthusiasts for its bulletproof reliability, lightweight design, and surprising tuning potential. Whether you're building a daily driver or a weekend track car, the aftermarket support for this platform is substantial. Skunk2, a brand synonymous with high-quality performance engineering, offers a range of D-series components that deliver real, dyno-proven gains without requiring a second mortgage. In this guide, we break down the top Skunk2 mods for your D-series engine, focusing on parts that can collectively produce over 30 horsepower for a total investment under $500 when shopped wisely. Each mod listed here costs under $500 individually, and by pairing the right upgrades—like a camshaft and an intake manifold—you can achieve substantial power increases through improved airflow and fuel delivery. Let's dive into the parts that transform your economy engine into a responsive powerhouse.

1. Skunk2 Intake Manifold

The factory intake manifold on most D-series engines is a study in compromise—designed for fuel economy and noise reduction, not performance. Skunk2 addresses this with a dual-runner design that dramatically improves airflow dynamics. The manifold features larger, smoother runners and a plenum volume tuned for mid-to-high RPM power, allowing your engine to breathe more freely. This upgrade is one of the highest-impact bolt-ons for the D-series, often yielding 10–15 horsepower on a properly tuned engine.

Key Features

  • Material: Cast aluminum with a durable black powdercoat finish.
  • Runners: 38mm primary and secondary runners for optimized velocity at low RPM and flow at high RPM.
  • Flange: CNC-machined sealing surface for a perfect gasket match.
  • Compatibility: Direct fit for most D-series heads (D15, D16, D17).

Performance Gains

When combined with a free-flowing exhaust and a tune, the Skunk2 intake manifold can add 10 to 15 wheel horsepower. The improvement in throttle response is immediately noticeable, especially from 4,000 RPM to redline. For best results, pair this manifold with a larger throttle body and a cold-air intake. Learn more about the manifold's design on the Skunk2 product page.

Installation Tips

Installation is straightforward but requires patience with the vacuum lines and throttle cable bracket. Use a new OEM or Skunk2 gasket, and consider upgrading to ARP intake manifold bolts for a secure fit. Expect about 2–3 hours of labor for a first-time installer.

2. Skunk2 Alpha Series Camshaft

The camshaft is the heart of any engine's power curve, and Skunk2's Alpha Series camshaft is engineered to unlock the D-series's top-end potential. With increased duration and lift compared to the stock cam, this shaft allows the valves to open wider and stay open longer, feeding more air into the cylinders at high RPM. This is the single best mod for peak horsepower on a naturally aspirated D-series build.

Key Features

  • Duration: 265 degrees of intake/exhaust duration (measured at 0.050 inch lift).
  • Lift: 11.5mm intake and exhaust valve lift.
  • Material: Billet steel core with hardened lobes for longevity.
  • Compatibility: Works with stock D-series valvetrain, but heavier valve springs are recommended for sustained high-RPM use.

Performance Gains

On a stock D16 with only a header and intake, the Alpha Series camshaft can contribute 12–15 horsepower gains in the upper range. Combined with the intake manifold above, you're looking at a 25–30 horsepower increase. Tuning is essential to dial in the Air/Fuel ratio and ignition timing—see tuning guides on Honda-Tech forums for basemaps. Price: approximately $250.

Installation Tips

Camshaft installation requires removing the valve cover, timing belt, and cam gear. Mark the timing belt position before removal. Always replace the cam gear bolts and use a new valve cover gasket. If you haven't upgraded the valve springs, limit RPM to 7,000 to avoid valve float.

3. Skunk2 Exhaust System

A performance exhaust system is the classic gateway mod, and Skunk2's offering reduces backpressure while enhancing the note of your D-series. Their cat-back systems are mandrel-bent from 2.5-inch 304 stainless steel for smooth flow and corrosion resistance. The muffler design eliminates restrictive baffles, allowing the engine to exhale freely.

Key Features

  • Diameter: 2.5-inch tubing (OEM is 1.75–2.0 inches).
  • Muffler: Straight-through design with a polished tip.
  • Sound: Deep and aggressive at full throttle, but not droning at highway speeds.
  • Hardware: Includes high-quality clamps and hangers.

Performance Gains

Expect 5–8 horsepower on a stock engine, and closer to 10 horsepower when paired with a header and intake. The biggest benefit is the improved torque curve, with gains starting as low as 2,500 RPM. Price: around $400. Check the SuperStreetOnline database for dyno plots from similar builds.

Installation Tips

Rubber hangers make removal straightforward, but if your car is from the rust belt, soak the bolts in penetrating oil overnight. The Skunk2 system is a direct bolt-on for most Civic/CRX chassis. Allow 2–3 hours for an easy install.

4. Skunk2 Short Shifter

While a short shifter doesn't add horsepower, it sharpens the driving experience and allows faster, more precise gear changes—critical when you're trying to keep the engine in the power band. Skunk2's short shifter reduces shift throw by 40% compared to the factory unit, using precision spherical bearings for a notchy, mechanical feel.

Key Features

  • Throw Reduction: 40% shorter shifts.
  • Bearing Type: Spherical pivot bearing for smooth operation.
  • Material: Billet aluminum base and lever.

Driving Benefits

The reduced throw means you can shift without removing your hand from the wheel, and the precise engagement reduces missed shifts in hard driving. While not a power mod, it's a $150 upgrade that makes every other mod feel more connected. Installation is under 1 hour and requires only basic hand tools.

5. Skunk2 Fuel Rail

As you increase airflow with the intake and camshaft upgrades, fuel delivery becomes a limiting factor. The Skunk2 fuel rail ensures consistent flow to each injector by increasing internal volume and eliminating the restrictive banjo fitting used on the OEM rail. This upgrade is especially important if you plan to run a fuel pressure regulator or larger injectors later.

Key Features

  • Material: Billet 6061 aluminum with a clear anodized finish.
  • Fittings: -6 AN inlet and outlet ports for high-flow applications.
  • Injector Spacing: Maintains OEM spacing for plug-and-play installation.

Performance Gains

On a naturally aspirated build with moderate upgrades, the fuel rail alone does not add horsepower, but it ensures that the other mods can reach their potential by preventing fuel starvation. Price: about $200. For builds exceeding 200 horsepower, combine this rail with a Skunk2 fuel pressure regulator for precise tuning.

Installation Tips

This is one of the easiest mods: unbolt the old rail, transfer the injectors and fuel lines, and bolt on the Skunk2 rail. Use new O-rings on the injectors to prevent vacuum leaks. Total time: 30 minutes.

6. Skunk2 Throttle Body

The throttle body is the gatekeeper of airflow into the engine. Skunk2's 64mm throttle body is a direct replacement for the stock 60mm unit, offering a 6.7% increase in cross-sectional area. This allows more air to enter the intake manifold at wide-open throttle, improving top-end power without sacrificing low-end response.

Key Features

  • Bore Diameter: 64mm CNC-machined.
  • Blade: Tapered throttle plate for predictable idle control.
  • Throttle Position Sensor: Retains OEM TPS for simple wiring.

Performance Gains

Combined with the Skunk2 intake manifold, this throttle body can add 3–5 peak horsepower and improve throttle response across the entire RPM range. On its own, the gain is more modest but still noticeable. Price: around $300. For a detailed comparison, visit the Skunk2 throttle body page.

Installation Tips

Remove the stock throttle body, transfer the TPS and IACV sensors, and install the Skunk2 unit with a new gasket. You may need to adjust the idle stop screw to achieve a stable idle. Expect 1 hour of work.

7. Skunk2 Coilovers

Horsepower is useless without traction, and Skunk2's coilovers give you the ability to dial in suspension stiffness and ride height. Their Pro-C series offers 32-way dampening adjustment and a 1–3 inch drop range. While this mod costs exactly $500—bringing the budget to its limit—it represents the final piece of a balanced performance setup.

Key Features

  • Dampening: 32-way adjustable for street or track tuning.
  • Height: Fully threaded shock bodies for independent height adjustment.
  • Spring Rates: 12k front / 10k rear for a firm but compliant ride.

Performance Benefits

Lowering the center of gravity and increasing spring rates reduces body roll in corners, allowing you to carry more speed through turns. This means you can use the horsepower from your other mods more effectively. Installation requires removing the old strut assembly and reassembling with the new coilovers—allow 3–4 hours.

Budget Consideration

If your goal is strictly power under $500, prioritize the camshaft and intake manifold. However, if you already have power mods and want to make them usable, the coilover upgrade is worth every penny. Read user reviews on D-Series.org for setup advice.

Conclusion: Building Your Under-$500 Power Package

Achieving over 30 horsepower on a D-series engine for under $500 is realistic if you choose the right combination of parts. The most effective path is to pair the Skunk2 Alpha Series Camshaft ($250) with the Skunk2 Intake Manifold ($350) for a total of $600—slightly over budget at retail. However, by sourcing one or both parts through seasonal sales, refurbished units, or enthusiast forums like Honda-Tech, you can bring the total under $500 while still seeing dyno gains of 25–30 wheel horsepower. Add a used Skunk2 throttle body ($150–$200) to push past 30 horsepower, or stick with the cam and intake and invest the savings in a performance tune. Each mod in this list is designed with the D-series in mind, and Skunk2's engineering ensures that every dollar spent moves you closer to a responsive, fun-to-drive Honda. Whether you choose a single high-impact upgrade or a carefully curated bundle, your D-series will thank you with a newfound sense of urgency.