Upper Intake Manifold Plenum for GMC Chevrolet CK 2500 3500 (1992-2002) 6.5L Diesel

Your 6.5L Detroit Diesel is a workhorse, but the factory intake design is choking it out. If you're tired of watching your EGT gauge climb every time you hit a grade, it’s time to remove the restriction that's been holding your turbo back since the 90s.

High-Flow Upper Intake Manifold Plenum for Chevy/GMC C/K 2500 & 3500 (6.5L Detroit Diesel)

Anyone who has spent time wrenching on the GMT400 platform knows the 6.5L Turbo Diesel has a love-hate relationship with airflow. While the block is stout, the factory induction system was designed with compromised geometry that creates turbulence right after the turbo compressor outlet. The stock upper intake plenum (often called the "intake hat") acts as a bottleneck, forcing charged air to hit a wall before it can effectively distribute into the lower manifold. This restriction keeps exhaust gas temperatures (EGTs) high and throttle response sluggish.

This replacement Upper Intake Manifold Plenum is designed to solve that specific architectural flow. By smoothing out the internal radius and opening up the volume, we reduce the pressure drop between your turbo and the engine valves. On a mechanically injected diesel like the 6.5L, efficiency is everything. This plenum allows your turbo to work less to move the same amount of air, resulting in a cooler, denser charge entering the cylinders.

Whether you are towing a heavy gooseneck with your K3500 or just trying to get your C2500 up to highway speeds without black smoke, this plenum is the foundational upgrade for intake efficiency. It bolts directly in place of the restrictive OEM unit, retaining factory mounting points while delivering the airflow dynamics that this V8 diesel should have had from the factory.

Why You Need This Upgrade

• Lower EGTs: improved airflow reduces the thermal stress on your cylinder heads, a critical reliability factor for the 6.5L.
• Faster Turbo Spool: Reducing the backpressure at the compressor outlet allows the turbocharger to build boost more linearly.
• Cleaner Combustion: More air to match your fuel delivery means less wasted unburnt fuel (black smoke) and better efficiency.
• Direct Fitment: Designed specifically for the bolt pattern of the 6.5L lower intake manifold, eliminating the need for fabrication.

Installation Notes

Installation is straightforward but requires care when working with aluminum threads. Ensure the mating surface on the lower intake manifold is completely clean of old gasket material before installation. We recommend checking the condition of your intake bolts and using a fresh gasket or high-temp RTV sealant suitable for diesel applications. Torque Specs: Always adhere to the factory torque specifications (generally 17-25 ft-lbs, but verify with your service manual) to avoid cracking the casting or stripping the lower intake threads.

Replaces These OEM Applications

• 1992-2000 Chevrolet C2500 (6.5L Turbo Diesel)
• 1992-2000 Chevrolet K2500 (6.5L Turbo Diesel)
• 1992-2002 Chevrolet C3500 (6.5L Turbo Diesel)
• 1992-2002 Chevrolet K3500 (6.5L Turbo Diesel)
• 1992-2000 GMC C2500 (6.5L Turbo Diesel)
• 1992-2000 GMC K2500 (6.5L Turbo Diesel)
• 1992-2002 GMC C3500 (6.5L Turbo Diesel)
• 1992-2002 GMC K3500 (6.5L Turbo Diesel)

Don't let a restrictive factory casting limit your truck's potential. Bolt on this high-flow plenum today and give your 6.5L the fresh air it needs to pull harder and run cooler.