How to Add 400 Horsepower to a Car

Adding about 400 horsepower to a car typically requires a large forced-induction setup (turbocharger or supercharger) or a high-output engine swap, plus comprehensive upgrades to fueling, cooling, drivetrain, and tuning. Expect a budget in the $15,000–$50,000+ range, significant shop time, and careful attention to reliability, traction, legal compliance, and safety. The exact path depends on your car’s baseline power, intended use, and local regulations.

Start With a Realistic Baseline

“Add 400 hp” means very different things depending on whether you’re starting at 150 hp or 500 hp, and whether you mean crank horsepower (factory rating) or wheel horsepower (measured on a dynamometer). Most factory engines and drivetrains are not engineered for a 400 hp jump on stock internals. Before you buy parts, define the goal (wheel vs. crank), choose your fuel (pump gas vs. E85 vs. race fuel), and decide whether the car is for street, track, or drag use. These choices drive everything that follows.

Main Paths to a +400 hp Gain

There are several proven strategies to add roughly 400 horsepower. The right choice depends on the platform, budget, and how you plan to use the car.

• Big turbo upgrade: Replace or add a large turbocharger with proper manifold, wastegate(s), intercooler, and charge pipes. Effective on modern turbo cars (e.g., performance I4s, I6s, V6s) where the engine architecture supports high boost. Often paired with upgrades to both high-pressure and low-pressure fuel systems and, at higher levels, forged internals.
• Positive-displacement supercharger: Roots or twin-screw kits deliver strong, immediate torque and can add 300–500+ hp on robust V8s (e.g., GM LS/LT, Ford Coyote, Mopar Hemi) with the right pulley, fuel, and tune. Heat management and octane become critical as boost rises.
• Centrifugal supercharger: Supports large top-end gains with less under-hood heat than PD blowers. Often chosen for road-course builds or where packaging and belt load are concerns.
• Engine swap (crate or OEM performance engine): Installing a higher-output engine (e.g., a supercharged V8 or a performance-spec inline-six) can leapfrog the complexity of heavily modifying a smaller or older engine. Requires extensive integration for mounts, wiring, cooling, exhaust, and emissions.
• Built engine plus forced induction: Tear down the original engine and add forged pistons, rods, upgraded bearings, head studs, and valvetrain, then turbocharge or supercharge. This route prioritizes longevity and headroom under high boost.
• Nitrous oxide (stacked or staged): Useful as a supplemental power adder for turbo or supercharged setups, but a full +400 hp on nitrous alone is extreme and generally demands a thoroughly built engine and exacting fuel/timing control.

For most platforms, a single big turbo or a supercharger on a stout engine, or a well-supported engine swap, are the most reliable ways to reach a +400 hp target. The more aggressive the path, the more critical the supporting systems and tuning become.

Supporting Mods You Cannot Skip

Power is limited by the weakest link. To add 400 hp safely, you need to upgrade the systems that feed, cool, contain, and control that power.

• Fuel system: High-flow injectors, upgraded low-pressure fuel pump, and (for direct-injection engines) a higher-capacity high-pressure pump. Consider port fuel injection add-on for DI engines at high power, flex-fuel sensor for E85, larger fuel lines, and a return-style system with a quality regulator.
• Intake and intercooling: Large front-mount intercooler or air-to-water setup, high-flow intake, and charge pipes. For superchargers, consider larger heat exchangers and pump upgrades to manage intake-air temperature.
• Exhaust and boost control: High-flow downpipe, headers, and exhaust with appropriate catalysts where legal. External wastegate(s) and a robust boost-control strategy to maintain stable, repeatable pressure.
• Engine internals and sealing: Forged pistons and rods, upgraded bearings, ARP head studs, multi-layer steel head gasket, improved crankcase ventilation, and stronger valvetrain components if you’ll spin higher RPM or run high boost.
• Cooling and lubrication: Aluminum radiator, high-capacity oil cooler, transmission cooler, differential cooler (for track use), and a baffled or larger oil pan to prevent oil starvation.
• Electronics and sensors: Programmable ECU or proven tuning solution, wideband O2, upgraded MAP sensors, ethanol content sensor for flex-fuel, and knock monitoring. Ensure sufficient ignition coil capacity and correct heat range spark plugs.

Skimping on these items is the fastest way to turn a big-power build into a short-lived one. Proper airflow, fueling, and heat control are non-negotiable at this level.

Drivetrain, Chassis, and Safety Upgrades

Once you add 400 hp, you must transmit it, stop it, and keep it under control. These upgrades make the power usable and protect the car—and you.

• Transmission and clutch/torque converter: High-clamp clutch or multi-plate unit for manuals; upgraded torque converter and reinforced internals for automatics; transmission cooling and revised tuning where applicable.
• Differential and axles: Limited-slip or upgraded diff, stronger axles/CVs, and appropriate final-drive gearing to match the new powerband.
• Tires and wheels: Wider, stickier tires (summer performance or drag radials as appropriate) and wheels rated for higher loads and heat.
• Brakes: Larger rotors, multi-piston calipers, high-temp pads, stainless lines, and high-boiling-point fluid. Power without stopping power is dangerous.
• Suspension and chassis: Stiffer bushings, coilovers or matched springs/dampers, traction/anti-hop kits, and chassis bracing. Alignment tuned for your use case (drag vs. road course vs. street).
• Safety: Roll bar/cage (as required by track rules), racing harnesses, proper seats, battery cutoff, and a fire suppression system for serious builds.

These upgrades turn raw horsepower into controllable performance. They also reduce the risk of component failure and improve consistency on road or track.

Tuning, Fuel, and Reliability

Tuning and fuel quality determine whether a big-power car is thrilling or fragile. Conservative timing and proper fueling beat peak dyno numbers if you want the engine to last.

The steps below outline a proven approach to calibration and verification:

1. Baseline and plan: Dyno the car in current form, define wheel vs. crank target, choose fuel (93 octane, E85, or race fuel), and verify compression and leak-down.
2. Sensor and control setup: Install wideband O2, ethanol content sensor (for flex-fuel), accurate MAP, and reliable boost control (wastegate springs, solenoids).
3. Fuel and spark calibration: Start rich and low timing; incrementally increase timing and boost while monitoring knock, EGTs, lambda, and IATs.
4. Thermal management: Validate intercooler efficiency and coolant/oil temps under repeated pulls; adjust ducting, heat exchangers, and fans as needed.
5. Part-throttle and drivability: Ensure smooth transitions, closed-loop control, and safe AFR under transient loads; calibrate idle and cold-start if injectors are large.
6. Validation: Multiple dyno sessions and road/track logs; verify repeatability in heat-soak and back-to-back runs.

E85 (or high-octane race fuel) often makes the difference between a safe tune and knock-limited power at this level. Flex-fuel setups add convenience but still require adequate pump and injector capacity.

Budget and Timeline

Costs vary widely by platform, parts quality, and how much labor you outsource. Here’s what most builders encounter when aiming for an additional 400 horsepower.

• Power adder kit: $4,000–$12,000 for turbo/supercharger hardware (more for custom fabrication or twin setups).
• Fuel system and intercooling: $2,000–$6,000 including injectors, pumps, lines, intercooler/heat exchanger, and sensors.
• Engine build (if required): $4,000–$12,000 for forged internals and machine work; more if sleeves, valvetrain, and head work are involved.
• Drivetrain and chassis: $3,000–$10,000+ for clutch/converter, transmission work, diff/axles, brakes, suspension, and tires.
• Tuning and dyno time: $800–$2,500+, depending on complexity and number of sessions.
• Labor and incidentals: $3,000–$10,000+ if using a shop; add contingency (10–20%) for surprises.

Project timelines often run 4–12 weeks with parts lead times and tuning iterations. Complex swaps or fully built engines can extend beyond that.

Legal and Insurance Considerations

High-power modifications can affect emissions compliance, inspections, and insurance coverage. Plan ahead to avoid costly setbacks.

• Emissions and inspections: In many regions, intake/exhaust and ECU changes must be emissions-legal. Look for parts with certification (e.g., CARB EO numbers in California) and maintain functioning OBD systems where required.
• Noise and equipment laws: Larger exhausts, external wastegates, and blow-off valves may violate local noise or equipment rules.
• Insurance and declarations: Notify your insurer of modifications; nondisclosure can void coverage after a claim. Consider specialty policies for modified vehicles.
• Track rules: Many tracks mandate roll-over protection, battery cutoffs, and specific safety gear above certain elapsed times or trap speeds.

A streetable, emissions-compliant 800–1,000 hp build is possible on some platforms with the right parts, but legality varies by jurisdiction. Confirm requirements before you commit.

Example Build Paths

These scenarios illustrate practical ways enthusiasts commonly achieve a ~400 hp increase, depending on platform strengths.

• Modern turbocharged six-cylinder: Upgrade to a larger turbo (or single-turbo conversion), high-capacity intercooler, DI and LPFP upgrades plus supplemental port injection, downpipe/exhaust, and flex-fuel. With forged rods/pistons and E85, many 3.0L turbo I6 platforms can add ~350–450 wheel hp reliably with expert tuning.
• American V8 with a supercharger: Install a 2.3–3.0L positive-displacement blower or a high-spec centrifugal kit, larger heat exchanger, injectors/pumps, headers, and a conservative pulley ratio on 93 octane or E85. Stock bottom ends on some V8s tolerate moderate boost; for +400 hp, a forged short block is strongly recommended.
• Engine swap into a lighter chassis: Fit a high-output crate or donor engine (e.g., supercharged V8 or performance inline-six) with standalone or integrated ECU, matched transmission, stronger diff/axles, big brakes, and cooling. This route can be more predictable than pushing a small OEM engine beyond its design limits.

Each path has trade-offs. Turbo builds often offer the best scalability; superchargers deliver instant torque; swaps can be the cleanest path to big numbers if you prefer OEM-like drivability.

Planning Checklist: From Goal to Road-Test

Use the following sequence to manage scope, control costs, and protect reliability as you pursue a +400 hp gain.

1. Define power goal, fuel type, and use case (street/track/drag) and set a realistic wheel vs. crank target.
2. Select the main path (turbo, supercharger, or swap) and verify platform-specific weak points.
3. Spec supporting systems: fueling, intercooling, exhaust, internals (if needed), cooling, and drivetrain.
4. Acquire parts with proven results on your platform; avoid mixing untested combinations.
5. Build/install with quality hardware, proper torque specs, and heat management (sleeving, heat wrap, shielding).
6. Calibrate on the dyno with conservative timing; validate with logs on the road or track under real heat and load.
7. Address traction, braking, and suspension; align to suit your intended use.
8. Finalize with reliability passes: repeat pulls, leak checks, fluid analysis, and retorques after initial miles.

Discipline in planning and verification pays dividends. Big power is easy to make; making it live is the true measure of a successful build.

Key Takeaways

Adding 400 horsepower is achievable on many modern platforms with a robust forced-induction setup or a well-integrated engine swap. The project’s success rests on supporting systems, expert tuning, and honest budgeting for drivetrain, cooling, and safety. For street cars, prioritize emissions legality and insurance disclosures; for track cars, meet safety rules and plan for heat management and repeatability.

Summary

To add roughly 400 hp, choose a major power-adder (big turbo or supercharger) or a high-output engine swap, then reinforce fueling, cooling, internals, drivetrain, and chassis. Use quality parts, conservative tuning—often on E85 or high octane—and budget substantial time and money. Done properly, the result is transformative performance with reliability that matches the power.

What is the cheapest way to add horsepower?

The cheapest and easiest ways to increase horsepower include installing a cold air intake to provide more dense air, upgrading to a high-flow exhaust system for better air exit, performing regular engine maintenance such as oil and air filter changes, and significantly reducing vehicle weight. For a more substantial increase, consider installing a performance chip or tune to optimize engine settings or, if your vehicle is turbocharged, installing a boost controller.
 
Low-Cost Mods

• Cold Air Intake: This system replaces the stock airbox and tubing, allowing the engine to draw in cooler, denser air for more efficient combustion and power. 
• High-Flow Exhaust: Upgrading to a less restrictive exhaust system (from the catalytic converter back) allows spent gases to exit more quickly, improving overall engine breathing and power output. 
• Regular Maintenance: Simply changing your engine oil, air filter, and spark plugs ensures your engine is running as efficiently as possible, helping it produce its maximum capable horsepower. 

Larger Investments for Bigger Gains

• Performance Chip/Tune: These can be installed to override factory settings, allowing you to adjust factors like the fuel-to-air ratio and ignition timing for significant performance gains. 
• Boost Controller (for turbocharged engines): For vehicles already equipped with a turbocharger or supercharger, a boost controller can safely increase the boost pressure, delivering more air into the engine and thus more power. 

Other Budget-Friendly Options

• Reduce Vehicle Weight: Opens in new tabBy removing unnecessary items from your trunk, such as heavy spare parts, or upgrading to lighter components like a lithium-ion battery, you can improve your car’s power-to-weight ratio. 
• Improve Engine Tuning (for naturally aspirated engines): Opens in new tabFor naturally aspirated (non-turbocharged) engines, a comprehensive upgrade path involves enhancing the exhaust, intake, and fuel system along with a proper engine tune. 

What adds the most HP to a car?

Supercharger or turbocharger
Also known as forced induction parts, both of these components force air into your car’s engine which improves horsepower and torque. A turbocharger works with the exhaust system and can potentially give you gains of 70-150 horsepower.

Is 400 horsepower a lot for a car?

Yes, 400 horsepower (HP) is a lot for a car, putting it in the territory of performance vehicles and significantly above the average for most standard vehicles. While once the realm of exotics, advances in technology have made 400 HP more accessible, but it still provides more than enough power for quick acceleration and a thrilling driving experience on most roads.
 
Why 400 HP is a lot

• Above Average: The average horsepower for standard vehicles is around 180-200 HP, so 400 HP is nearly double that, according to J.D. Power. 
• Performance-Oriented: 400 HP is the benchmark for many sports cars, muscle cars, and luxury performance vehicles. 
• Modern Accessibility: Technologies like turbocharging and direct injection have made it possible for a wider range of vehicles, including everyday cars, to offer 400 HP or more, a feat that was once the sole domain of high-performance models. 

What 400 HP means for you

• Fast Acceleration: You can expect brisk acceleration and a powerful response from the engine, especially when you press the gas pedal. 
• Performance Thrills: A car with 400 HP will offer a significant accelerative thrill that is distinct from a less powerful vehicle. 
• Practical for the Street: 400 horsepower is more than enough for virtually any street-driven vehicle and provides ample power for daily use, according to Jalopnik and Bimmerpost. 

How fast is 240 HP in mph?

Horsepower (hp) does not convert directly to miles per hour (mph); horsepower is a unit of power (energy over time), while mph is a unit of speed. A vehicle’s top speed in mph depends on its horsepower in conjunction with many other factors like its aerodynamics, weight, drivetrain, and gear ratios. 
Key Factors Influencing Top Speed

• Horsepower: A higher horsepower output generally allows a vehicle to achieve a higher top speed by overcoming resistance. 
• Aerodynamics: How streamlined a vehicle is (its drag coefficient) plays a significant role. A car with a more aerodynamic shape will have a higher top speed at the same horsepower level. 
• Weight: A lighter vehicle requires less power to accelerate to a given speed, and thus can achieve a higher top speed with the same amount of horsepower. 
• Drivetrain & Gears: The vehicle’s transmission and final drive ratio affect how efficiently the engine’s power is transferred to the wheels, influencing the achievable speed at a given engine RPM. 
• Rolling Resistance: The friction between the tires and the road also consumes power, affecting the final speed. 

What a 240 hp Vehicle Might Achieve

• A moderately sized car with good aerodynamics and 240 hp could realistically be capable of a top speed around 150 mph. 
• However, a less aerodynamic vehicle, like an SUV or truck with the same horsepower, would likely have a much lower top speed due to higher drag.