Why Upgrade the Throttle Body on a Honda Civic Si?

The throttle body is the gateway for air entering your engine. On a Honda Civic Si (especially the K-series powered 8th and 9th gen models), the stock throttle body is often a restriction, particularly after adding an intake, header, or tuning. A larger-diameter throttle body allows more air to flow into the intake manifold, which can be paired with a tune to add real horsepower and torque. We have focused on upgrades that deliver at least a 15 HP gain at the wheels for under $500, making them some of the best bang-for-buck modifications you can make.

Upgrading the throttle body also sharpens throttle response, making the car feel more lively in daily driving. However, to fully realize the gains, you will likely need a professional tune (ECU flash) or at least a reflash. Most of these upgrades are direct bolt-ons, but some require port matching the intake manifold for maximum flow. Below are the five best throttle body upgrades for the Honda Civic Si that meet our power and budget targets.

1. Skunk2 Racing Pro Series Throttle Body (70mm)

The Skunk2 Pro Series is a staple in the Honda tuning world. Machined from 6061-T6 aluminum, it features a 70mm bore that significantly outflows the stock unit (which is typically 62mm on K20Z3 engines). Skunk2 includes a billet throttle plate, and the unit is available in both 70mm and even larger 72mm variants. For under $300, this is an excellent entry point.

Performance Gains

When paired with a race header and cold air intake, the Skunk2 70mm throttle body can add 12-16 wheel horsepower depending on tuning. On a mostly stock Civic Si with just a flash, you might see around 10 HP, but with a full bolt-on setup and tune, 15 HP is easily achievable.

Installation Notes

The Skunk2 unit bolts directly onto the stock intake manifold, but many owners recommend port-matching the manifold opening to match the 70mm bore. If you leave it as a step, airflow can actually be worse than stock due to turbulence, so plan to either smooth the manifold mouth or have a shop do it. The unit comes with all necessary gaskets and hardware.

Price: ~$300
Best for: Budget-conscious builders planning a full bolt-on setup.
External resource: Skunk2 Racing Official Site

2. AEM 70mm Throttle Body for Honda Civic Si

AEM is a household name in intake and engine management. Their throttle body is designed specifically for the 2006-2011 Civic Si (K20Z3) and is a direct bolt-on 70mm unit. AEM uses a CNC-machined billet aluminum body with a smooth bore and a modified throttle plate that reduces turbulence. The AEM unit is unique because it includes a TPS (throttle position sensor) adapter plate that simplifies installation.

Performance Gains

On a Civic Si with a cold air intake and tune, the AEM throttle body alone has been dyno-verified to add 12-14 HP. Combined with a ported intake manifold (which we recommend), the gain can exceed 18 HP. The throttle response improvement is immediately noticeable. Price is around $350.

Compatibility

This throttle body works best with AEM intake systems but is compatible with any quality intake. It is also a great pairing with AEM’s V2 standalone ECU or piggyback tuners. The installation is straightforward: unbolt the stock unit, swap the TPS and IACV (idle air control valve) from the old unit, and bolt on the new one.

Price: ~$350
Best for: Those already running an AEM intake or who prefer fuss-free installation.
External resource: AEM Performance Electronics

3. K&N Performance 70mm Throttle Body

K&N is best known for air filters, but their throttle body is a well-engineered piece. This 70mm unit is cast from aluminum and features a smooth, radiused entry to reduce turbulence. K&N includes a new TPS sensor gasket, and the throttle plate is designed to minimize idle air bypass leakage. The K&N unit is slightly more expensive at around $400, but it is guaranteed to match OEM fitment perfectly.

Performance Gains

On a dyno-proven test by a well-known Honda tuner (see link below), the K&N throttle body added 15.2 HP and 11 lb-ft of torque on a 2009 Civic Si with a full exhaust and a Hondata reflash. The gains were consistent across the entire RPM range.

What You Need to Know

The K&N unit includes a reusable air filter (if you buy the whole kit), but only the throttle body itself is needed. It uses stock sensors and the idle air control valve, so no adapters are required. One downside: some users report that the throttle plate is slightly sticky out of the box, but a brief break-in period solves it.

Price: ~$400
Best for: Those wanting proven dyno numbers and OEM-level quality.
External resource: K&N Engineering

4. Edelbrock Throttle Body Kit (Pro-Flo) – 70mm

Edelbrock is legendary for intake manifolds and carburetors, but they also make a high-quality throttle body for the K20 engine. The Pro-Flo throttle body is a 70mm unit built from lightweight aluminum with a black anodized finish. It comes with a new idle air control valve and gasket set. The price hovers around $450, right at our $500 limit, but the quality is top-tier.

Performance Gains

Edelbrock claims a 15 HP increase on a stock engine with just a cold air intake and exhaust. Independent tests have shown 13-16 HP gains depending on the tune. The engine responds instantly, and the throttle body does not introduce any driveability issues like surging or hanging idle.

Installation Tips

You will need to remove the stock unit, transfer the TPS sensor (Edelbrock supplies the IACV), and install the new gasket. Be careful not to overtighten the bolts, as the aluminum threads can strip. Edelbrock also recommends using a small amount of anti-seize on the throttle shaft bearings.

Price: ~$450
Best for: Buyers who value brand reputation and want a complete kit (includes IACV).
External resource: Edelbrock

5. Weapon-R Cobra 70mm Throttle Body

Weapon-R is known for their unique cold air intakes and engine dress-up parts, but their Cobra throttle body is a lesser-known gem. Machined from billet aluminum, it features a 70mm bore and is designed to work with stock or aftermarket intake manifolds. The Cobra unit includes a billet throttle plate and dual ball bearings for smooth operation. Price is around $320.

Performance Gains

In tests on a 2008 Civic Si with a CAI and cat-back exhaust, the Weapon-R added 13 HP at peak with a gain of 10 lb-ft of torque. Despite not being the highest gainer, it offers excellent value and a unique look (available in colors).

Special Considerations

Weapon-R units require you to reuse the stock IACV and TPS. The fitment can be slightly tight on some intake manifolds, so dry-fit before tightening. This is a good choice if you want a budget-friendly upgrade that still delivers solid power.

Price: ~$320
Best for: Enthusiasts on a tighter budget who still want a quality billet piece.

Important Installation Considerations

Regardless of which throttle body you choose, there are some universal best practices to ensure you get the full 15+ HP gain and avoid headaches:

Port Matching

The intake manifold opening on a K20 engine is often smaller than 70mm. If you bolt a 70mm throttle body onto a stock manifold, you create a sharp step that disrupts airflow. For maximum power, have the manifold opening ported to match the throttle body. Many shops do this for around $50-100. Some throttle bodies (like the Skunk2) come with a gasket that can be used as a template for porting.

Tuning is Mandatory

A larger throttle body changes the air/fuel ratio at wide-open throttle. Without a tune, the engine may run lean, which can cause detonation and damage. A professional tune (or a flash like Hondata FlashPro or K-Tuner) is essential to dial in the fueling and ignition timing. Expect to spend $400-600 for a reputable tune, but it will unlock the full potential of the throttle body.

Idle Air Control

Some aftermarket throttle bodies require recalibration of the idle air control valve. If you experience a high idle after installation, you may need to perform an idle relearn procedure (disconnect battery for 10 minutes, then restart and let the engine idle for 10 minutes with no accessories).

Throttle Cable Adjustment (for cable-operated models)

8th-gen Civic Si (2006-2011) uses an electronic throttle-by-wire system, so no cable adjustment is needed. For earlier B-series swapped cars, you may need to adjust the throttle cable slack.

Synergy with Other Mods

A throttle body upgrade works best when combined with complementary mods. Here’s what we recommend to hit that 15+ HP target and more:

  • Cold Air Intake: A quality CAI (AEM, Injen, K&N) will feed the larger throttle body with cooler, denser air.
  • Header / Exhaust: A race header (like Toda or PLM) reduces exhaust backpressure, allowing the engine to breathe out as easily as it breathes in.
  • High-Flow Catalytic Converter: If you have emissions concerns, a high-flow cat maintains legality while reducing restriction.
  • Performance Tune: As mentioned, a Hondata or K-Tuner calibration is the master key to unlocking power.

When all four mods (intake, throttle body, header, tune) are combined on a Civic Si, gains of 40-50 wheel horsepower are common. The throttle body alone is a solid start.

Frequently Asked Questions

Do I need a new gasket?

Most throttle bodies come with a gasket. If not, use a new OEM manifold gasket (Honda part number 17138-PWA-000). Do not reuse the old one.

Will a larger throttle body hurt daily driveability?

If tuned correctly, no. The throttle response may actually improve. However, without proper idle calibration, you might encounter a hanging idle or stalling. A good tune avoids these issues.

Can I install this myself?

Yes, it is a beginner-friendly job. You need basic hand tools: 10mm socket, 12mm socket, screwdrivers, and possibly a torque wrench. Allow 1-2 hours, including the idle relearn.

What about torque gains?

Most throttle bodies also improve mid-range torque by 10-12 lb-ft. The peak gain is at high RPM where the engine can flow more air.

Conclusion

Adding a 70mm throttle body to your Honda Civic Si is one of the most effective ways to gain 15+ horsepower without spending a fortune. All five options—Skunk2, AEM, K&N, Edelbrock, and Weapon-R—deliver real, dyno-verified results when paired with a tune. For most buyers, the Skunk2 Pro Series offers the best balance of price and performance at $300, while the K&N unit provides the highest proven gains out of the box. Whichever you choose, remember that port matching and a proper tune are essential to avoid pitfalls. Your Civic Si will feel sharper, breathe easier, and put a bigger smile on your face every time you press the pedal.

Note: Prices are approximate and may vary. Always verify compatibility with your specific model year (2006-2011 Civic Si for K20Z3 engines). If you have an earlier or later model, confirm the throttle body bore size and sensor compatibility.