There are many options for upgrading your Hemi. On a stock engine, the following upgrades can improve performance and fuel economy:
These engines have a 3.917 in. bore diameter. The thin wall casting should be bored no more than .030 in. over. Anything larger requires sleeves or an Upgraded Block.
Stock pistons are a known weak point. They will crack ring lands in higher horsepower engines. A set of Forged Pistons should be high on your priority list.
The factory rods are powdered metal with a cracked cap design and can handle about 650 hp. If you're getting forged pistons, upgrade to Forged Connecting Rods at the same time.
The OE cast crankshaft can handle about 650 hp and 7,000 rpm (for a limited time). Upgrading to a Forged Crank early in your build will save you headaches later. The forged crank from a 6.1 is a fantastic upgrade with the same 3.578 in. stroke. If you’re going to upgrade, a 4.050 in. stroke crankshaft costs about the same and increases displacement. Just be sure you have the correct reluctor ring for your application.
Factory Gen 3 Hemi heads flow very well but still respond to porting and polishing. They can be milled for more compression. However, stock compression is already in the 10:1 range. To go much higher, you need to run race gas. Consider proactively replacing the valve seats on higher mileage heads as they are known to be a problem.
It is possible to use the 2009 and newer “Eagle” heads. They flow better but require an Eagle intake, valve covers, custom pushrods, and a .075 thickness head gasket to keep compression down to 11:1.
Many Aftermarket Heads are available. They flow better and have thicker decks to maintain head gasket seal. A wide range of runner and chamber volumes are available.
Camshaft and Valvetrain
Gen 3 Hemis respond well to Cam Upgrades. In addition to valve springs and pushrods, the cam needs to match the compression, torque converter, rear-end gears, etc. Keep in mind, piston-to-valve clearance is tight with cams over 230° duration @ 0.050 in.
The factory rockers are good for 7000rpm. Roller Tip Rockers are available for those that wish to upgrade.
Intake Manifold and Throttle Body
Porting is a popular option for stock intake manifolds. At 80mm, the factory throttle body won't be a restriction in most applications. When you swap one of these engines, we recommend using an Aftermarket Intake Manifold. Just be sure to match the intake port shape on the heads. Most aftermarket intakes are designed to accommodate larger 92mm or 102mm Throttle Bodies.
Fuel System and Tuning
Truck engines have a conservative tune from the factory. Tuning the computer changes the fuel and ignition curves to increase performance. Plug-In programmers are relatively easy to use, but they do have limits. Custom tuning requires more knowledge but can provide even better performance.