Best 103mm LS3 Throttle Body: Granatelli Billet vs. Nick Williams vs. FAST

The factory LS3 throttle body is 90mm. Once you add a cam, headers, a bigger intake or boost, that 90mm blade becomes one of the first restrictions in the intake tract, and a 102mm–103mm drive-by-wire throttle body is the most common next step.

When enthusiasts ask which big-bore LS3 throttle body to buy, three names keep coming up: the Granatelli 103mm billet, the Nick Williams 103mm and the FAST 102mm Big Mouth. Here is how they compare on the specs that actually matter.

Granatelli vs. Nick Williams vs. FAST: Spec Comparison

Specs and prices below are from each seller's published listing as of November 2026.

The bottom line: all three are in the same price range, but they are not the same deal. The Nick Williams 103mm needs an aftermarket intake, which can add a lot to the cost of the upgrade. The Granatelli 103mm billet works with your stock LS3 intake, carries a published 35 psi boost rating, comes in two finishes and is made in the USA. If you want a bigger throttle body without buying a new intake, or you are building a supercharged or turbocharged LS3, the Granatelli is the one built for the job.

No Aftermarket Intake Required

A lot of big-bore throttle bodies only make sense once you have already bought an aftermarket intake manifold. The Granatelli 103mm billet works with the factory LS3 intake, so you can step up from the stock 90mm throttle body now, and it still works if you upgrade to an aftermarket intake later. Just make sure your intake tube and coupler fit the larger inlet.

Why Billet Matters

The Granatelli GMTBLS3 and GMTBLS3B are CNC-machined from 6061-T6 billet aluminum. Billet gives a precise bore and a rigid body that holds its shape under heat and boost, which matters for a part that has to hold a tight blade-to-bore fit for consistent electronic throttle control.

Built for Boost: 35 PSI, Draw-Through or Blow-Through

On a boosted LS, the throttle body sits in the pressurized side of the intake on a blow-through setup, or in front of the compressor on a draw-through setup. Granatelli rates the 103mm billet to 35 psi in either configuration, so it is a fit for centrifugal superchargers, turbo kits and high-boost street builds.

Plug-In Drive-By-Wire

The Granatelli 103mm is a complete assembly. It plugs into the GM 6-pin drive-by-wire connector, and nothing has to be transferred from your factory throttle body. A tune is required for proper electronic throttle operation and drivability.

Which Granatelli LS3 Throttle Body Should You Choose?

• GMTBLS3: 103mm billet, silver ($680.79)
• GMTBLS3B: 103mm billet, black ($680.79)
• GMTBLS3M: 103mm cast ($445.13): the budget 103mm option.
• GMTBLS108: 108mm billet ($811.72): for combinations that need more than 103mm.

See every size in Granatelli LS throttle bodies.

Common Mistakes

• Skipping the tune. A drive-by-wire throttle body needs a tune for proper throttle control and idle.
• Buying an intake you don't need. Some 103mm throttle bodies require an aftermarket intake. The Granatelli 103mm billet works with the stock LS3 intake.
• Forgetting the intake tube. A larger inlet may need a matching intake tube and coupler.
• Assuming any 6-pin plug fits. Confirm your connector; never force a plug or use a look-alike adapter.

LS3 Throttle Body FAQ

What is the best 103mm throttle body for an LS3?

The Granatelli 103mm billet (GMTBLS3 silver / GMTBLS3B black) is CNC-machined from 6061-T6 billet, works with the stock LS3 intake and aftermarket intakes, plugs into the GM 6-pin drive-by-wire connector, carries a published 35 psi boost rating and is made in the USA, at $680.79.

Does the Granatelli 103mm throttle body fit a stock LS3 intake manifold?

Yes. It works with the factory LS3 intake and with aftermarket intake manifolds, so no aftermarket intake is required.

Is the Granatelli 103mm throttle body good for boost?

Yes. It is rated to 35 psi of boost in draw-through or blow-through configurations.

Do I need a tune?

Yes. A tune is required after installation.

Which engines does it fit?

Compatible GM LS applications with 6-pin drive-by-wire, including LS1, LS2, LS3, LS6, LS7, LS9, LSA, LSX, LQ4 and LQ9 when the correct DBW configuration is used. Trailblazer SS owners should call before ordering.

Where is it made?

Machined by Granatelli Motor Sports in Oxnard, California, USA.

Questions about fitment? Call Granatelli Motor Sports at 1-805-486-6644, Monday–Friday, 8am–5pm PST.

Written by JoJo Granatelli — third generation at Granatelli Motor Sports in Oxnard, California, and the one who drives what the company builds. He set a quarter-mile record of 7.06 seconds at 157 mph at Famoso Dragstrip in August 2026. More about JoJo.