The HEMI at Heart: What Makes the Challenger R/T Special?

The 5.7-liter HEMI V8 in the Challenger R/T is a proven workhorse. It punches well above its displacement with Variable Valve Timing (VVT) and the Multi-Displacement System (MDS) for better fuel economy when cruising. This engine delivers roughly 370–375 horsepower and 400 lb-ft of torque from the factory, offering a strong foundation without the thirst of its 6.4-liter (392) or supercharged Hellcat siblings. Because the 5.7 HEMI shares the same basic architecture as its larger cousins, the aftermarket support is vast. Yet, the very features that make it livable—MDS, a modest compression ratio, and a conservative factory tune—are often the first things owners consider changing when looking for more power. The challenge lies in making intelligent upgrades that avoid common pitfalls like ring land failures or valvetrain instability.

Related Reading: Hot Rod’s 5.7 HEMI Build Guide – a deep dive into the engine’s strengths and limits.

Engine Modifications: Building Horsepower Without Breaking Reliability

Adding power to the 5.7 HEMI is relatively straightforward, but each modification must be evaluated for how it stresses the rotating assembly, the cooling system, and the drivetrain. The goal is to gain usable power without triggering knock, excessive heat, or oil starvation.

Air Intake and Throttle Body

Replacing the restrictive factory intake with a cold air intake (CAI) provides minimal gains (10–15 hp) but reduces intake air temperatures. For daily drivers, a CAI is one of the safest mods because it doesn’t increase engine stress. Pairing it with a larger 85mm or 90mm throttle body can improve throttle response, but gains above 5–10 hp require other supporting mods. Stick with name-brand kits that include heat shielding to avoid pulling hot under-hood air.

Exhaust and Headers

Long-tube headers are a popular upgrade that can net 20–30 hp on the 5.7 HEMI. However, they can cause check-engine lights if the secondary O2 sensors are not properly tuned. A high-flow catted mid-pipe or cat-back exhaust system improves exhaust velocity. For daily driveability, avoid headers with extremely short primaries (which sacrifice low-end torque) and choose a muffler system that stays under 85 dB to prevent drone on the highway. A Borla ATAK or Corsa Xtreme pair well with the HEMI’s natural note without being obnoxious.

Camshaft Upgrades

Installing a performance camshaft is where the trust-reliability trade-off becomes critical. A moderate 212°–220° intake duration cam with 0.550–0.580 in lift can safely make 430–450 hp with a tune, while retaining the factory MDS solenoids (if you disable MDS in software). Aggressive cams above 230° duration require stronger valve springs and often necessitate deleting MDS, which increases valvetrain noise and reduces highway fuel economy by 3–5 mpg. Keep in mind that the factory pistons are hypereutectic and become fragile above 500 hp. If you plan on a cam swap, budget for a custom tune, new valve springs, pushrods, and likely an upgraded oil pump (gerotor style) to handle increased RPMs.

Forced Induction vs. Naturally Aspirated

Many R/T owners consider adding a centrifugal supercharger (e.g., ProCharger or Vortech) to reach the 500–600 hp range. While a safe 6–7 psi intercooled kit can be reliable on the stock bottom end, the factory fuel system (injectors and pump) will reach its limit around 550 crank hp. To go beyond that, you need a boost-referenced fuel pump and larger injectors. A better path for most daily drivers is to stay naturally aspirated with a cam, headers, and a custom tune—this keeps heat cycling lower and avoids the complexity of an intercooler system. If you choose forced induction, invest in a larger heat exchanger (for the intercooler) and an oil catch can to prevent detonation from oil vapor ingestion.

Learn More: HEMI News: 5.7 Supercharger Build Lessons

Drivetrain Upgrades: Matching the Power to the Pavement

The stock 5-speed (2008–2014) or 8-speed (2015+) automatic transmissions are stout but not invincible. Over 500 lb-ft of torque, the 8HP70 found in later models can slip if the torque converter clutch is not tuned properly. For manual cars (rare), the TR-6060 tremec is strong but the clutch and flywheel must handle the extra torque. A common weak point is the limited-slip differential, especially on 2.92- or 3.06-gear cars. Upgrading to 3.73 or 4.10 gears dramatically improves acceleration but reduces highway RPMs slightly—a worthwhile trade for real-world punch. Ensure the differential fluid is changed regularly and consider a differential cooler if you track the car.

Torque Converter Selection

If you have an automatic, a higher-stall torque converter (2,400–2,800 rpm) allows the engine to stay in the power band. For daily use, avoid converters above 3,200 rpm as they cause excessive heat and make stop-and-go driving feel sluggish. A billet cover and heavy-duty pump are recommended for any converter over 2,800 rpm.

Suspension and Brakes: The Unsung Heroes of Driveability

Coilovers vs. Lowering Springs

The Challenger’s weight (over 4,100 lbs) means a stiff suspension can quickly become punishing. High-quality adjustable coilovers, such as those from KW or BC Racing, allow you to dial in damping for the street while maintaining enough control for cornering. For most daily drivers, a 1–1.5 inch drop paired with custom-valved shock absorbers and matched springs is the sweet spot. Avoid cutting stock springs or using cheap sleeve coilovers, which cause bump stops to engage, leading to a jarring ride and reduced tire contact.

Brake Rotors and Pads

With more power, you need to stop. The base R/T uses single-piston sliding calipers with 13.6-inch rotors. Upgrading to Brembo 4- or 6-piston calipers (from a 392 Scat Pack or SRT) provides significantly better pedal feel and fade resistance. At minimum, swap to high-performance pads like Hawk HPS or Power Stop Z23, and replace brake fluid with DOT 4 for track days.

Daily Driveability: Keeping the R/T Comfortable and Reliable

Reliability for a daily driver is not just about engine internals—it’s about the small annoyances that make a car hard to live with. Here are key considerations:

  • Fuel Economy: A cammed R/T may drop from 20–22 mpg highway to 16–18 mpg. For a daily commuter, this adds up. Consider keeping a conservative tune for daily driving and a second “performance” tune for weekends.
  • AC and Electrical Load: Upgraded fuel pumps and electric fans impose higher loads on the charging system. Ensure your alternator is in good health (stock 160A is usually sufficient), and upgrade the battery to a high-cranking-amp AGM unit.
  • Heat Management: The stock cooling system is adequate for stock power but can struggle in summer stop-and-go traffic with a supercharged engine. Upgrade to a larger radiator (e.g., Mishimoto or Ron Davis) and a 180°F thermostat. Also consider a transmission cooler if you are auto.
  • Interior NVH: Long-tube headers and a camshaft can increase cabin drone, especially at 40–60 mph. Research exhaust systems with J-pipes or Helmholtz resonators to cancel out drone frequencies. Sound deadening mats (like Kilmat or Dynamat) under the carpet can help reduce road noise.

Oil and Maintenance: The Forgotten Foundation

The 5.7 HEMI is sensitive to oil quality. Use a synthetic 5W-30 that meets Chrysler MS-6395 (e.g., Pennzoil Ultra Platinum or Mobil 1). Change oil every 3,000–4,000 miles if you drive hard or have a supercharger. The factory valve covers can collect condensation in cold weather, so a catch can is strongly recommended for any modified engine to prevent carbon buildup on intake valves (since the 5.7 does not have direct injection, but crankcase blowby still causes deposits).

Reference: Allpar’s HEMI Oil Guide – detailed filtering and viscosity advice.

Putting It All Together: A Realistic Build for 400–450 Reliable Horsepower

An achievable daily-driver build that retains factory reliability looks like this:

  1. CAI + ported throttle body – +10–15 hp ($400)
  2. Long-tube headers + high-flow cats – +20–25 hp ($1,200)
  3. 2.5-inch cat-back exhaust – sound enhancement, minor gains ($700)
  4. “Stage 2” camshaft (212° intake/0.550 lift) with MDS delete and new springs – +50–60 hp ($2,000 including tune)
  5. Custom 91-octane tune (safely targeting 420–440 wheel hp) – $500–800
  6. 3.73 gears (if automatic with 2.92 or 3.06) – significantly improves throttle response ($1,500 installed)
  7. Performance brake pads + DOT 4 fluid – $300
  8. Coilovers (adjustable) + alignment – $1,500
  9. Larger radiator + 180° thermostat – $600
  10. Oil catch can – $100

Total investment: ~$8,000–9,000 for a car that runs mid-12s in the quarter-mile, retains air conditioning, drives smoothly on the highway, and won’t leave you stranded. This leaves the engine stock bottom end safe, the transmission unmodified (8-speed), and the cooling system up to the task. Many owners report 50,000+ trouble-free miles with this level of modification when maintained properly.

What About Warranty and Emissions?

If your R/T is under warranty, modifications will void coverage for related components. Consider keeping all factory parts and waiting until the warranty expires. For emission testing, ensure your 50-state-legal CARB EO if you live in a strict area; many cam kits and headers are not CARB-legal, so you may need to reinstall factory pieces for smog check.

Avoiding Common Mistakes

  • Over-tuning: Pushing timing beyond 12° BTDC on pump gas without knock sensors calibrated can lead to melted pistons. Always use a reputable tuner (like Hennops or DiabloSport).
  • Ignoring the Drivetrain: 500 hp at the crank is useless if you can’t put it down. Upgraded tires (e.g., 275/40R20 or 305 rear) are mandatory. Consider wider wheels (10.5–11 inches) to fit rubber.
  • Neglecting Cooling: A big power radiator is cheap insurance. Overheating causes head gasket failures—a $3,000 repair on a HEMI.
  • Under-specifying Transmissions: If you swap to a manual, use a clutch rated for 550+ lb-ft to avoid slipping when merging on the highway.

The Verdict: Enjoy the R/T as a Balanced Daily

The Dodge Challenger R/T is a brilliant platform precisely because it can be both a comfortable cruiser and a potent street machine. With careful selection of parts—prioritizing drivetrain durability, heat management, and a conservative tune—you can exceed the power of a stock Scat Pack while retaining the ability to commute in traffic, run errands, and take road trips. The golden rule is to enhance the car in layers rather than rushing to the highest number. By respecting the 5.7’s limits and addressing its weak points (cooling, differential gears, brakes), you will end up with a car that is faster than 90% of vehicles on the road, yet as reliable as a modern sedan.

Final Resource: 350HP.org: Challenger R/T Build Diaries – community-sourced data on long-term reliability of modified 5.7s.