Quadrajet Carburetors

The Q-Jet's Unique Performance Advantage

The Quadrajet is inherently suited to the Pontiac V8's characteristic high torque output. Its design philosophy is the key:

• Primary Bores: The small primaries provide excellent throttle response and superior fuel atomization during light-throttle cruising. This is what gives the Q-Jet its reputation for better fuel economy than comparable square-bore carburetors.

• Secondary Bores: The massive secondary bores, capable of flowing up to 800 CFM on most performance models, act like a vacuum-actuated power-on-demand system. When the driver demands power, those huge flaps open to unleash a flood of air and fuel, perfectly matching the Pontiac engine's ability to consume massive amounts of air at mid-to-high RPMs.

Stage-Tuned for Pontiac Power

Butler Performance provides specialized Q-Jets—often partnering with premier builders like JET Carburetors and utilizing their own custom specifications—to overcome the common pitfalls of stock units and maximize performance. These carburetors are calibrated specifically for the Pontiac V8 (350ci, 400ci, 455ci) running on modern fuel.

Stage 1: The Enhanced Stock Replacement

The Stage 1 Quadrajet Carburetor (800 CFM) is the ideal solution for stock or lightly modified Pontiac engines. This stage focuses heavily on reliability and fixing factory flaws:

• Epoxy Sealing: Butler-spec Stage 1 Q-Jets address the notorious problem of fuel leak-down by sealing the main body casting plugs with epoxy. This prevents fuel from draining into the intake manifold, eliminating hard-starting issues and lean-out conditions.

   

• Throttle Shaft Bushing: The carburetor receives a rebuild with bronze-bushed throttle shafts to eliminate common vacuum leaks that occur as the stock shafts wear.

   

• Precision Tuning: All fuel circuits are checked and calibrated with Pontiac-specific jets and metering rods to ensure correct fuel delivery across the entire RPM range for a stock or near-stock application.

   

Stage 2: Performance Calibration for Modified Engines

The Stage 2 Quadrajet Carburetor (800 CFM) is engineered for Pontiac engines with performance upgrades, such as aluminum cylinder heads, headers, and a mild performance camshaft.

• Full Recalibration: Stage 2 units feature fully re-calibrated idle, off-idle, main, accelerator pump, and high-speed circuits. This precise tuning is essential to ensure the carburetor complements the increased airflow and vacuum characteristics of a modified engine.

   
   

• Maximum Response: This level of tuning is designed to deliver improved idle quality, instant throttle response, and maximum torque and horsepower from a modified street engine.

   

• Modern Convenience: The units are typically supplied with a modern electric choke for reliable cold starts and consistent warm-up performance.

   

Essential Tuning and Reliability Features

The Quadrajet carburetors offered through Butler Performance incorporate key features that enhance both tuning flexibility and long-term durability:

• Adjustable Part Throttle (APT): Many high-performance Quadrajets include an APT feature, allowing the builder to precisely tune the cruise-speed and part-throttle air/fuel mixture without disassembling the carburetor. This is a massive advantage for street tuning.

   

• High-Quality Components: Only the highest quality components are used, including high-flow needle and seat assemblies, solid composite floats, and premium gaskets to ensure longevity and compatibility with modern ethanol-blended fuels.

   

By offering these custom-spec Quadrajet solutions, Butler Performance allows Pontiac enthusiasts to honor the original equipment design while harnessing modern tuning knowledge to unlock incredible power and streetability from their classic V8.