Boosting Your Lifted Smart Car's Performance: Engine and Transmission Upgrades

The 2008-2015 Smart Fortwo 451 is a quirky, ultra-compact city car that's beloved for its efficiency and maneuverability. Powered by a rear-mounted 1.0-liter three-cylinder naturally aspirated engine, stock models deliver around 70 horsepower. Paired with a five-speed automated manual transmission, it's nimble in traffic but can feel underwhelming on highways or when you crave a bit more excitement. Fortunately, the aftermarket scene offers plenty of ways to amp up performance without sacrificing the car's charm. At Braapus.com, we're all about transforming these tiny titans into something special. Whether you're looking for subtle performance improvements or full-blown power surges for your lifted smart car, we've got you covered with engine and transmission upgrade recommendations. We'll break them down into mild, moderate, and extreme categories to suit different budgets, skill levels, and driving goals. Remember, these mods can enhance throttle response, acceleration, and top speed, but always prioritize safety and check local regulations.

Mild Upgrades: Subtle Enhancements for Everyday Driving

If you're new to modding or just want a noticeable but low-risk boost, start here. These upgrades focus on optimizing airflow, ignition, and basic tuning to wake up the engine without major overhauls. Expect gains of 5-10 hp, better throttle response, and a throatier exhaust note. Transmission tweaks are minimal but can smooth out shifts.

• Cold Air Intake and Performance Air Filter: Replace the stock airbox with a high-flow intake system like the Sila Concepts or BMC setup. This draws in cooler, denser air for improved combustion efficiency. Paired with a washable K&N or BMC filter, you'll feel peppier low-end torque. Cost: $100-300. Installation is straightforward and reversible.

• Performance Exhaust System: A cat-back exhaust from brands like Sila Concepts reduces backpressure, allowing the engine to breathe easier. Options include center or side-exit designs for a sportier sound. Gains are modest (2-5 hp), but the improved flow enhances overall responsiveness. For transmission synergy, this pairs well with mild ECU tweaks to prevent bogging during shifts. Cost: $200-1,300.

• ECU Tune or AutoFlash Module: A basic remap from tuners like MADNESS or OE Tuning adjusts fuel mapping and ignition timing. Expect better throttle sensitivity and a slight power bump. The MADNESS AutoFlash is a plug-and-play option that doesn't require sending out your ECU. Transmission benefits include refined shift points for less hesitation. Gains: Up to 5-10 hp/torque. Cost: $200-500.

• Upgraded Spark Plugs and Ignition Coils: Denso Iridium plugs and high-performance coil packs ensure stronger sparks for cleaner burns. This is especially useful in older 451s to combat misfires and improve efficiency. No direct transmission impact, but smoother engine operation reduces strain on the clutch. Cost: $50-150.

• Performance Engine Mounts: Stiffer mounts from MADNESS minimize engine movement, leading to crisper power delivery and better transmission engagement. This upgrade sharpens the driving feel without adding power. Cost: $100-200.

These mild mods keep things reliable and emissions-friendly, making them ideal for daily commuters who want a funner drive.

Moderate Upgrades: Noticeable Power Without Going Overboard

For enthusiasts ready to invest more, moderate upgrades build on the basics with deeper tuning and hardware swaps. You can push 10-30% power increases. Transmission upgrades become key here to handle the extra torque.

• Advanced ECU Remap: Specialists like BIG Performance, Bluespark, or Dynotronics offer custom tunes that optimize fuel delivery and rev limits. See 5-10 hp gains with better response. Include a gearbox remap to quicken shift times and reduce lag in the automated manual—transforming it from sluggish to snappy. Gains: 10-25 hp/20-40 lb-ft. Cost: $300-600.

• Upgraded Clutch Kit: The stock clutch can slip under increased power, so swap in a performance unit from Sachs, EXEDY, or Smart Hard Tuning. These handle 30-35% more torque, with options like twin-friction plates for better grip. Essential for transmission longevity when adding engine mods. Includes clutch fork and related hardware for a full refresh. Cost: $400-800.

• MADNESS Power Pack Stage 1 or 2: These kits bundle intake, exhaust, and ECU tuning for cohesive gains. Stage 1 focuses on bolt-ons for 10-15 hp, while Stage 2 adds ignition upgrades and remaps for 15-25 hp. Transmission benefits from tuned shift logic to match the power curve. Cost: $500-1,000.

• Performance Exhaust and Intake Combo: Parts from Sila Concepts or equivalents provide a balanced upgrade path. The sport exhaust pairs with a cold air intake for freer breathing, and when tuned, delivers a more aggressive driving experience. For transmission, ensure the remap addresses any increased load. Gains: 10-20 hp overall.

Expect 0-60 mph times to drop by a second or two, making highway merges more confident. Professional dyno tuning is recommended to avoid reliability issues.

Extreme Upgrades: Turning Your 451 into a Pocket Rocket

If you're chasing serious performance—think 150+ hp in a 1,800-pound car—these upgrades require commitment, including potential engine internals and custom fabrication. Ideal for track days or show builds, but expect higher maintenance and possible warranty voids.

• Turbo Kit for Naturally Aspirated Models: Kits from Speed Force Racing (SFR) bolt on a turbocharger, intercooler, and piping. Stage 1 adds basic boost for 100-115 hp, while Stage 3 with upgraded fueling pushes 158 hp at the wheels. Requires ECU remapping and often a stronger clutch. Transmission must be tuned for quicker shifts to handle the surge. Gains: 40-90 hp. Cost: $2,000-5,500.

• Big Turbo and Supporting Mods: Add larger turbos from SFR or Smart Hard Tuning. Include bigger injectors, high-flow fuel pump, and methanol injection for Stage 3+ builds reaching 160-200 hp (or even 300 hp with extensive mods). ECU remaps are mandatory, boosting torque dramatically. Transmission upgrades include heavy-duty clutches and reinforced actuators to prevent failures. Gains: 50-200+ hp. Cost: $3,000-10,000+.

• Engine Swap or Full Build: Drop in a tuned engine or rebuild the 1.0L with forged internals for high-boost setups. Combine with gearbox remaps for lightning-fast shifts and higher rev limits. Extreme kits from SHT Performance include methanol kits for cooling under boost. This turns the 451 into a mini-supercar, but reliability drops without proper cooling and oiling upgrades.

• Comprehensive Transmission Overhaul: Beyond clutches, add a custom actuator and software flash to mimic a true manual feel. For extreme power, some builders reinforce the gearbox housing or swap to stronger units from other models.

These mods can shave seconds off acceleration, but they're not for the faint-hearted—budget for dyno time, custom tuning, and potential repairs.

Final Thoughts

Upgrading your Smart Fortwo 451's engine and transmission can breathe new life into this pint-sized performer, from mild tweaks for city zipping to extreme builds that surprise sports cars at stoplights. Start small to test the waters, and always consult pros for installation to maintain safety and drivability. At Braapus.com, we do our best to offer performance advice based on our experiences and tailored to your goals. Drive smart, drive fast!