5.7 HEMI vs 6.4 HEMI: Which Engine is Better for Mods?

The Starting Point Matters

Before you can plan your build, you need to understand what you're starting with. The 5.7L and 6.4L HEMI are both Gen III pushrod V8s, but they have meaningful differences in displacement, compression, internals, and how they respond to modifications.

5.7L HEMI (R/T) — The Facts

• 392 cubic inches? No — despite the name, the 5.7L displaces 345 cubic inches (5.7 liters)
• Stock power: 375 HP / 410 lb-ft torque
• Compression ratio: 10.5:1
• MDS: Yes on automatic models — deactivates 4 cylinders at cruise
• Cam: Smaller factory cam profile than the 6.4
• Block: Slightly different casting than the 6.4; smaller bore at 3.917"
• Price advantage: R/T models cost $6,000–$10,000 less than a Scat Pack

6.4L HEMI (Scat Pack / SRT392) — The Facts

• 392 cubic inches — 6.4 liters, larger bore at 4.090"
• Stock power: 485 HP / 475 lb-ft torque (2022 model)
• Compression ratio: 10.9:1
• MDS: Yes on automatic models
• Cam: More aggressive factory profile than the 5.7
• Apache connecting rods: Stronger forged rods from the factory
• Variable valve timing: Yes — improves torque curve across the RPM range

Mod Potential: How Each Responds

Cold Air Intake + Tune

Both engines respond similarly to intake and tune — expect 15–25 WHP on the 5.7, and 20–35 WHP on the 6.4. The 6.4's larger displacement means more air volume moved per cycle, so the percentage gain is similar but the absolute number is higher.

Camshaft

This is where the gap widens significantly. A Stage 2 cam on a 5.7 can push it to around 430–450 WHP with supporting mods. The same Stage 2 cam on a 6.4 reaches 520–560 WHP. The larger bore and more aggressive stock cam profile of the 6.4 gives it a higher ceiling.

Forced Induction

Both engines accept supercharger and turbo kits. The 6.4's stronger Apache rods handle boost better at stock, though both will need forged internals for serious (700+ HP) builds. On the 5.7, the smaller bore limits ultimate power potential.

Headers

Both respond well to long-tube headers — expect 25–35 HP gains on a properly tuned 5.7, and 30–40 HP on the 6.4.

Reliability Comparison

The 5.7 has a longer production history with more data. Lifter failure (the HEMI tick) affects both, but the 5.7 has a slightly higher reported rate, partly due to the smaller oil pump flow relative to the engine size. The 6.4's Apache rods are stronger than the 5.7's cast rods.

Both are very reliable with proper maintenance. Neither has a major known weakness beyond the universal HEMI tick risk.

Cost to Get to 500 WHP

• 5.7 to 500 WHP: Cam + heads + headers + intake + tune + supporting mods. Budget $5,000–$8,000 in parts. Very achievable.
• 6.4 to 500 WHP: Headers + cam + tune + intake. Budget $3,500–$5,500. Easier and cheaper to reach the same number.

Which Should You Buy?

Buy the 5.7 (R/T) if:

• Budget is the priority — use the savings to mod
• You're building a street/strip car and want a lower base price
• You're okay with more work to reach 500+ HP

Buy the 6.4 (Scat Pack) if:

• You want the most stock performance per dollar
• You plan to stay mostly bolt-on (the 6.4 makes great power without a cam)
• You want the stronger factory internals for future boost plans

For most builders, the Scat Pack's 6.4 is the better starting platform for high-power builds. The R/T is a fantastic daily driver that can still be built into a very fast car — it just takes more work and money to match the 6.4's ceiling.