Baseline Performance And Specifications Of A Stock 1991 Nissan 240sx

Alright, let's talk about the 1991 Nissan 240SX. Specifically, let's dive into its baseline performance and specifications when it rolled off the assembly line, bone stock. This is crucial information, whether you're restoring a classic, using it as a drift missile, or just want to understand its original design intent. Knowing the baseline provides a solid foundation for any modifications or repairs you undertake.

Engine and Drivetrain

The heart of the '91 240SX is the KA24DE engine. This is a 2.4-liter (2389cc) inline four-cylinder engine featuring dual overhead camshafts (DOHC) and four valves per cylinder. This configuration significantly improved breathing compared to its single-cam predecessor. The "DE" designation indicates Dual overhead cams and Electronic fuel injection.

Engine Specifications

Displacement: 2389 cc (2.4 liters)
Bore x Stroke: 89 mm x 96 mm (3.50 in x 3.78 in) - This long-stroke design contributes to good low-end torque.
Compression Ratio: 9.5:1
Fuel System: Electronic Fuel Injection (EFI) - Specifically, Nissan's ECCS (Electronic Concentrated Control System)
Horsepower: 155 hp (116 kW) @ 5600 rpm - This is the factory-rated output. Expect some variation due to age and condition on existing vehicles.
Torque: 160 lb-ft (217 Nm) @ 4400 rpm - The usable torque curve is one of the KA24DE's strengths.
Redline: Approximately 6500 rpm. Hitting the rev limiter feels like hitting a wall, so avoid it.

Important Note: These figures are for a healthy, well-maintained engine. Factors like worn piston rings, carbon buildup, and poor maintenance can significantly reduce these numbers. A compression test is your friend when assessing engine health. Ideally, all cylinders should be within 10% of each other.

Drivetrain

The KA24DE engine sends power to the rear wheels through either a 5-speed manual transmission (FS5W71C) or a 4-speed automatic transmission (RE4R01A).

5-Speed Manual (FS5W71C): A robust and relatively simple transmission. Known for its durability. Common issues include worn synchros, especially in 2nd and 3rd gear, leading to grinding during shifts.
Gear Ratios (Approximate): 1st: 3.321, 2nd: 1.902, 3rd: 1.308, 4th: 1.000, 5th: 0.838, Reverse: 3.382
4-Speed Automatic (RE4R01A): Less desirable for performance applications but provides ease of use. Considerably heavier and saps some of the engine's power.
Gear Ratios (Approximate): 1st: 2.785, 2nd: 1.545, 3rd: 1.000, 4th: 0.694, Reverse: 2.272
Final Drive Ratio: Usually 4.083:1 (varies slightly depending on model and transmission). This ratio affects acceleration and top speed. A lower (numerically higher) ratio provides quicker acceleration but reduces top speed.

The 240SX utilizes an open differential as standard. This means that power is always sent to the wheel with the least amount of traction. For drifting or performance driving, many owners swap to a limited-slip differential (LSD) to improve traction and predictability.

Chassis and Suspension

The 240SX boasts a fully independent suspension, contributing to its well-regarded handling. It uses MacPherson struts in the front and a multi-link suspension in the rear. This setup offers a good balance between comfort and performance.

Suspension Components:

Front: MacPherson struts with coil springs and lower control arms. A sway bar (anti-roll bar) connects the two sides to reduce body roll during cornering.
Rear: Multi-link suspension with coil springs and upper and lower control arms. Also features a sway bar. The multi-link design allows for more independent control over wheel movement, improving handling.
Steering: Power-assisted rack and pinion steering. Provides a direct and responsive feel. Common issues include power steering pump leaks and worn tie rod ends.

Spring Rates: Stock spring rates are relatively soft, prioritizing ride comfort over outright performance. Upgrading to stiffer springs and dampers is a common modification for improved handling. Baseline spring rates are typically around 2.5-3.0 kg/mm in the front and 2.0-2.5 kg/mm in the rear.

Alignment Specifications (Factory): Understanding the factory alignment settings is crucial, especially if you're trying to restore the car to its original handling characteristics.

Caster: Typically around 4.0 degrees (positive). Caster influences steering stability and straight-line tracking. Camber: Generally around -0.5 to -1.0 degrees (negative). Negative camber improves grip during cornering. Toe: Usually close to zero or slightly "toe-in". Toe affects tire wear and straight-line stability.

Note: These settings are a starting point. Many owners adjust these values based on their driving style and intended use.

Brakes

The 1991 240SX features disc brakes on all four wheels. This provides adequate stopping power for everyday driving. The front discs are vented, which helps dissipate heat and reduce brake fade under heavy use.

Front Brakes: Vented disc brakes with single-piston calipers.
Rear Brakes: Solid disc brakes with single-piston calipers.
Brake Booster: Vacuum-assisted brake booster for improved braking feel and reduced pedal effort.

Common Issues: Brake fade under heavy use (especially with stock pads), warped rotors, leaking brake lines, and a failing master cylinder.

Wheels and Tires

Stock wheels were typically 15x6 inch alloy wheels with a +40mm offset. Tire size was generally 195/60R15. These provided a comfortable ride and adequate grip for the car's performance level.

Tire Pressure: Recommended tire pressure is usually around 32 PSI (pounds per square inch), but this can vary depending on the tire type and driving conditions. Consult the tire sidewall for the maximum allowable pressure.

Performance Figures (Stock)

Keep in mind these are estimates based on factory data and independent testing. Actual performance can vary depending on the car's condition, driver skill, and environmental factors.

0-60 mph: Approximately 8.0-8.5 seconds (Manual Transmission). The automatic transmission is noticeably slower.
Quarter Mile: Around 16.0-16.5 seconds.
Top Speed: Approximately 135 mph (electronically limited in some markets).

Weight

Curb weight for the 1991 240SX coupe is around 2700-2800 lbs (1225-1270 kg), depending on options. The hatchback is slightly heavier. Weight distribution is roughly 55% front and 45% rear, contributing to the car's tendency to oversteer.

Why This Matters

Understanding these baseline specifications is more than just trivia. It's essential for:

Troubleshooting: Knowing the expected performance can help you identify potential problems. If your engine is down on power, comparing it to the factory specifications can help pinpoint the cause.
Modifications: This knowledge is crucial for planning modifications. Understanding the stock spring rates, for example, will help you choose appropriate aftermarket springs.
Restoration: If you're restoring a 240SX, knowing the original specifications is vital for maintaining its authenticity.
Tuning: Properly tuning an engine requires knowing its original parameters. You can't effectively tune an engine if you don't know what it's supposed to be doing in the first place.

By familiarizing yourself with these details, you'll be well-equipped to work on, modify, and appreciate the 1991 Nissan 240SX.