Introduction: What Are FAST LS3 Individual Throttle Bodies?

The FAST LS3 Individual Throttle Bodies (ITB) kit is a high-performance upgrade designed for GM LS-series engines, particularly the LS3 and LSX variants. Unlike a conventional single throttle body that restricts airflow through a single opening, an individual throttle body setup assigns one throttle plate to each intake runner. This design dramatically reduces intake manifold volume and pressure drop, resulting in sharper throttle response, increased peak horsepower, and a more aggressive intake sound.

Installing a FAST LS3 ITB system can unlock 20–40+ horsepower gains on a mild LS3 build, with even larger improvements on forced-induction or high-compression engines. However, the installation is more involved than swapping a single throttle body. This guide provides a complete, production-focused walkthrough to ensure you get the most from your FAST ITB kit.

Before beginning, review the official FAST documentation at FAST’s website for your specific kit part number, and consider referencing a tuning guide such as the HP Tuners VCM Suite manual for post-install calibration.

Tools, Materials & Safety Equipment

Having the right tools on hand before you start will avoid frustration. Below is a comprehensive list. Some items are optional but recommended for a professional result.

Required Tools

  • Socket set – ¼” and ⅜” drive, with metric (most LS bolts are 10mm, 13mm, 15mm) and SAE sizes for throttle body bolts (often 5/16” or 8mm hex).
  • Torque wrench – capable of inch-pounds (in-lb) for small bolts and foot-pounds (ft-lb) for larger fasteners.
  • Flathead screwdriver – for prying electrical connectors and prying apart stubborn gaskets.
  • Phillips screwdriver – for hose clamps and some accessory brackets.
  • Ratchet extension – at least a 6” and a 12” extension to reach deep bolts.
  • Gasket scraper – plastic or brass to avoid gouging aluminum surfaces.
  • Throttle body cleaner – specifically a “sensor-safe” formula (do not use carb cleaner on electronic components).
  • Shop towels and lint-free rags – for cleaning and wiping gasket surfaces.
  • Safety glasses and gloves – always protect eyes and skin from fuel, coolant, and debris.
  • Vacuum gauge – to check for leaks after installation.
  • Coolant drain pan and drip funnel – if you plan to remove the coolant crossover (often needed).
  • Thread-locking compound (blue Loctite) – for throttle body bolts that may vibrate loose.
  • Digital caliper – for verifying throttle plate centering.
  • Battery terminal brush – to clean the battery post before reconnecting.

Preparation: Setting Up Your Workspace and Engine

Choose a well-ventilated, clean workspace. If possible, raise the vehicle on jack stands or ramps to access the engine bay comfortably. Allow the engine to cool completely – at least two hours after shutdown – to avoid burns and to prevent gaskets from warping when removed.

Disconnect the battery by removing the negative terminal. Wrap the cable end with a rag to prevent accidental contact. This is critical for preventing short circuits during the removal of the intake manifold (which may have live sensor wires).

If your vehicle uses a coolant crossover that sits on top of the intake manifold, you will need to drain the coolant system. Place a drain pan under the radiator petcock, open it, and remove the radiator cap to allow flow. For LS engines with a steam line, disconnect it and cap the fitting to avoid spills.

Next, remove the engine cover (if equipped) by unbolting the four 10mm bolts and lifting it straight up. Set the cover aside.

Step-by-Step Installation

Step 1: Remove the Intake Manifold

Start by unplugging all electrical connectors from the intake manifold: the throttle position sensor (TPS), idle air control (IAC), manifold absolute pressure (MAP) sensor, and any EVAP solenoid connectors. Note their positions – take a picture with your phone for reference.

Disconnect vacuum hoses, especially the brake booster line, PCV valve hose, and any emissions system lines. Use a flathead screwdriver to loosen worm-gear clamps.

Using a socket and extension, remove the intake manifold bolts in a reverse of the factory torque sequence (start from the outer bolts and work inward to prevent warping). There are typically 8 or 10 bolts on an LS intake manifold. Lift the manifold carefully off the engine. If it sticks, use a plastic trim tool to gently pry around the gasket area – do not force it.

Once the manifold is off, inspect the intake ports on the cylinder head. Cover them with clean rags or tape to prevent debris from falling in during the rest of the installation.

Step 2: Clean the Gasket Surfaces

Use a gasket scraper and a lint-free rag wetted with throttle body cleaner to remove all traces of the old intake gasket material from both the cylinder head surface and the new FAST ITB base. Be meticulous – even a tiny piece of old gasket can cause a vacuum leak. If the old gasket is stubborn, apply a silicone gasket remover spray, let it sit for 10 minutes, then scrape.

After scraping, wipe the surfaces with brake cleaner or throttle body cleaner until a clean rag comes away spotless. Allow the cleaner to evaporate fully before continuing.

Step 3: Install the New Gaskets

Your FAST LS3 ITB kit should include a set of dedicated gaskets (often multi-layer steel or composite). Do not reuse old gaskets. Place each gasket onto the cylinder head intake port studs (if your heads are drilled for studs) or position them directly over the ports. Ensure the gasket’s sealing surface aligns perfectly with the port opening – a misaligned gasket will cause a massive leak.

Pro tip: Some installers apply a thin, even film of high-temp gasket sealer (like Permatex Ultra Copper) to the cylinder head side of the gasket to help retain it while positioning the ITB assembly. Use sparingly – you want the gasket to be replaceable later.

Step 4: Mount the FAST LS3 Individual Throttle Bodies

Carefully lift the ITB assembly (which comes pre-assembled with the linkage and TPS/IAC) onto the gaskets. The throttle bodies are individual units mounted on a common base plate. Align each throttle body bore with its corresponding port. The bolt holes should line up perfectly with the gasket and the cylinder head threads.

Torque specification: FAST recommends tightening the mounting bolts to 89 in-lb (10 Nm) in a crisscross pattern. Do not exceed this – aluminum threads can strip easily. Use a torque wrench set for inch-pounds. If your kit uses studs and nuts, torque the nuts to the same spec.

After initial tightening, verify that all throttle plates still open and close freely without binding. The linkage should snap back to idle with a spring action. If any plate sticks, loosen the bolts slightly, reposition the assembly, and retorque.

Step 5: Reinstall the Intake Manifold (If Applicable)

Some FAST ITB kits are designed to work with the factory intake manifold as a secondary manifold (usually for long-runner applications). In that case, you will need to reinstall the original intake manifold after the ITBs are mounted. Follow the factory service manual procedures – clean the manifold sealing surface, install new gaskets, and torque the manifold bolts to the factory specification (typically 8 ft-lb for the first pass, then 18 ft-lb final).

If your kit replaces the intake manifold entirely (common with “sheet metal” style intakes that bolt directly to the ITB base), skip this step.

Step 6: Reconnect All Hoses and Electrical Connectors

Reattach the vacuum hoses to their correct ports. The FAST ITB base may include dedicated ports for the brake booster, PCV, fuel pressure regulator (if return style), and MAP sensor. Use new hose clamps where needed.

Plug in the IAC and TPS connectors. Ensure the connectors are fully seated and click into place. Reconnect the MAP sensor if it was removed. Reinstall the engine cover if desired (though many leave it off for the aesthetic look of the ITBs).

If you drained coolant, fill the system with fresh coolant (50/50 mix of distilled water and approved coolant for your vehicle). Run the engine with the radiator cap off to burp trapped air. Top off as needed.

Step 7: Reconnect the Battery

Reinstall the negative battery terminal and tighten it securely. Use a terminal brush to clean any corrosion before reconnecting.

First Start, Idle Adjustment & Tuning

With everything assembled, start the engine. The initial idle may be rough or high because the IAC position and TPS voltage need calibration. Allow the engine to reach operating temperature (approximately 185°F coolant temp).

Check for vacuum leaks: With the engine idling, use a vacuum gauge connected to a manifold vacuum port. Normal vacuum on a healthy LS engine is 17–22 inHg at idle. If you see a low or erratic reading, spray carb cleaner around the throttle body gaskets while listening for RPM changes – a sudden rise indicates a leak.

Idle speed adjustment: The FAST ITB kit may include an adjustable idle air screw. Turn it clockwise to lower idle, counterclockwise to raise idle. Aim for a stable idle between 850 and 1000 RPM for a street engine with a manual transmission; automatic transmissions may require slightly higher idles in gear.

TPS calibration: Most aftermarket ECUs (like Holley Terminator X, FAST XFI, or HP Tuners) allow you to set the TPS voltage. With the key on (engine off), measure the TPS signal voltage. Set closed-throttle voltage to approximately 0.65V – 0.75V. Open throttle fully and record the maximum voltage (usually around 4.5V). This is critical for proper throttle response and transmission shift scheduling.

For a comprehensive tuning guide, consult Holley EFI’s tuning resources and the HP Tuners help center.

Troubleshooting Common Issues

Issue Likely Cause Solution
High idle (1500+ RPM) IAC stuck open, vacuum leak, or throttle linkage not returning fully Check IAC pintle clearance, verify linkage return spring tension, smoke test for leaks.
Rough idle / stumbling Throttle plates not synchronized, or low TPS voltage Use a synchronizer tool to balance throttle plates; re-calibrate TPS.
Hesitation on tip-in Lean condition due to small injectors or improper IAC step position Enrich fuel through tuning; increase IAC position at idle.
Check engine light (CEL) TPS or IAC circuit fault, or large vacuum leak triggers lean code Scan for DTCs, inspect wiring, use a multimeter to verify sensor signals.

Maintenance and Longevity

Individual throttle bodies require more frequent cleaning than standard fuel injection systems because the intake air passes directly through throttle plates without a large manifold to trap dirt. Use a sensor-safe throttle body cleaner every 15,000 miles or at every oil change. While cleaning, inspect the linkage for wear and lubricate pivot points with a light machine oil.

Also check the adjustment of the idle set screw and ensure all 8 throttle plates are still synchronized. Over time, vibration can shift the linkage alignment. A simple synchronizer tool (available from many performance shops) can restore balance in minutes.

If you drive in dusty or off-road conditions, consider installing a high-flow air filter box that encloses all eight trumpets. This will protect the blades from sand and grit that could score the bore surface.

Performance Expectations

After a proper installation and tune, expect a noticeable improvement in throttle response – the engine will “snap” to attention compared to a single throttle body. On a naturally aspirated LS3, dyno results from FAST show gains of 15–25 lb-ft of torque in the mid-range and 20–35 horsepower at peak, depending on other modifications (cam, headers, compression). The sound also changes dramatically – the individual throttle bodies produce a distinct “sucking” noise at high RPM that many enthusiasts love.

For forced-induction engines (supercharged or turbocharged), ITBs can present a unique tuning challenge because vacuum signal is diminished under boost. However, with a proper blow-through setup and dedicated MAP reference, ITBs can deliver excellent power and response.

Real-world results from the community can be explored on LS1Tech forums, where many builders share their ITB dyno sheets and installation tips.

Final Thoughts

Installing a FAST LS3 Individual Throttle Body kit is one of the most rewarding upgrades you can perform on an LS platform. The mechanical complexity is higher than a simple manifold swap, but the payoff in throttle response, power, and auditory drama is unmatched. Follow this guide carefully, respect torque specifications, invest in a quality tune, and your engine will repay you with a thrilling driving experience.

If you encounter a step you are not comfortable performing – especially wiring or calibration – seek help from a professional engine builder or tuner. The FAST technical support team can also assist with kit-specific questions.