Tools in This Collection
HP to Torque Calculator
Convert between horsepower and torque at any RPM
Quarter Mile Calculator
Estimate trap speed and ET from horsepower and weight
Gear Ratio Calculator
Optimize acceleration vs top speed with gear ratio changes
Engine Displacement Calculator
Calculate total displacement from bore, stroke, and cylinder count
RC Gear Ratio Calculator
Optimize gear ratios for RC vehicles
Motorcycle Chain Calculator
Size chains and sprockets for motorcycle builds
Performance Calculation Workflow
Performance tuning requires understanding how power, torque, gearing, and weight interact. The key formula connecting them: horsepower = torque x RPM / 5252. A 300 lb-ft torque peak at 4,500 RPM produces exactly 257 HP at that RPM. This relationship governs every performance decision from cam selection to gear ratios.
Horsepower and Torque
The HP to Torque Calculator converts between horsepower and torque at any RPM. Use it to understand where your engine makes peak power versus peak torque — the power band is the RPM range where both are strong. For a naturally aspirated engine with peak torque at 3,500 RPM and a 6,500 RPM redline, the useful power band spans roughly 3,500-6,000 RPM. Shifting at peak HP (not peak torque) maximizes acceleration.
Quarter-Mile Time Estimation
The Quarter Mile Calculator estimates trap speed and ET from horsepower and vehicle weight using the Halderman formula. A 3,200 lb car with 350 HP should run approximately 12.8s at 108 mph. Real-world results vary by traction, driver skill, and launch RPM — but the calculator gives a useful baseline for comparing build options before committing parts money.
Gear Ratio Optimization
The Gear Ratio Calculator shows how different final drive and transmission ratios affect acceleration versus top speed. Numerically higher gear ratios (e.g., 3.73 vs 3.08 rear end) increase acceleration and engine RPM at highway speed — good for drag racing, worse for fuel economy. Lower ratios (3.08, 2.73) reduce highway RPM for better efficiency at the cost of off-the-line punch.
Engine Displacement
The Engine Displacement Calculator computes total engine displacement from bore, stroke, and cylinder count. The formula: displacement = bore² x stroke x 0.7854 x cylinders. A 4-cylinder with 87mm bore and 91mm stroke displaces 87² x 91 x 0.7854 x 4 = 2,164cc — approximately a 2.2L engine. Displacement directly influences torque output and power potential.
RC and Motorcycle Gearing
The RC Gear Ratio Calculator optimizes gear ratios for RC vehicles. The Motorcycle Chain Calculator helps size chains and sprockets for motorcycle builds, including aftermarket sprocket swaps that change final drive ratio for street or track use.
Frequently Asked Questions
What is the difference between horsepower and torque?
Torque is rotational force — how hard the engine twists the crankshaft. Horsepower is torque multiplied by RPM (divided by 5252), meaning it accounts for how fast that force is delivered. High torque at low RPM gives strong off-the-line pull (diesel trucks). High HP at high RPM gives strong top-end acceleration (sports cars). The HP to Torque Calculator shows both values across the RPM range.
How do I choose a gear ratio for better acceleration?
Higher numeric gear ratios (3.73, 4.10, 4.56) multiply torque multiplication at the wheels, giving stronger acceleration but more engine RPM at highway speed. For street/strip use, 3.73 is a common balance point. Pure drag builds often use 4.10-4.56. Highway-only drivers prefer 3.23 or lower. The Gear Ratio Calculator shows RPM at highway speed for each option.
How accurate is the quarter-mile time estimator?
The quarter-mile calculator uses the Halderman formula (ET = 6.269 x (weight/HP)^0.33) which is accurate to within 3-5% for street cars with adequate traction. Real-world results depend on launch RPM, traction, driver skill, altitude, and temperature. Use it to compare build options — a 50 HP gain on the same platform will show proportional improvement in the estimate.