Loading...
Calculate engine horsepower from bore, stroke, compression ratio & aspiration. Advanced calculator with BMEP, specific output & geometry analysis. Free tool for engine builders & tuners.
Higher CR = more power but requires higher octane fuel. Typical: 8-11:1 (NA), 7-9:1 (Turbo)
HP per liter. Higher = more efficient. NA: 50-100 HP/L, Turbo: 100-200+ HP/L
Indicates engine efficiency. Higher = better torque. Good: 150-200 psi
kW per ton. Higher = better acceleration. Sports cars: 150-300+ kW/ton
Higher RPM capability, more power-oriented. Common in sports engines.
More torque, better fuel efficiency. Common in diesel and economy engines.
Balanced design offering good power and torque characteristics.
Linear power delivery, simpler design. VE: 80-95%
Exhaust-driven, lag present. Efficient, high power potential. VE: 100-150%
Belt-driven, instant response. Consistent boost. VE: 100-130%
Input bore diameter (cylinder width) and stroke length (piston travel distance). Enter number of cylinders (4, 6, 8, etc.). Calculator automatically computes displacement.
Enter compression ratio (typically 8:1 to 14:1 for naturally aspirated). Set volumetric efficiency (80-95% for stock engines). Adjust RPM for peak power calculation.
Select naturally aspirated, turbocharged, or supercharged. For forced induction, enter boost pressure in PSI. Calculator adjusts power output accordingly.
View horsepower, torque, BMEP, specific output, and engine geometry metrics. Compare different configurations to optimize performance.
The diameter of the cylinder. Larger bore allows bigger valves and better breathing. Measured in mm or inches.
Example: 86mm bore = 3.39 inches
Distance the piston travels from top to bottom. Longer stroke increases displacement and torque.
Example: 86mm stroke = 3.39 inches
Higher RPM capability, better breathing, more horsepower-focused. Common in performance engines.
Balanced design with good power and torque. Efficient combustion and moderate RPM range.
More torque at lower RPM, better fuel efficiency. Common in diesel and truck engines.
Compression ratio is the ratio of cylinder volume at bottom dead center (BDC) to volume at top dead center (TDC). Higher compression increases thermal efficiency and power but requires higher octane fuel.
Turbocharged engines, forced induction, regular fuel compatible
Modern naturally aspirated engines, premium fuel recommended
Performance engines, requires premium fuel, higher efficiency
Race engines, E85 or race fuel required, maximum efficiency
BMEP measures engine efficiency independent of size. It represents the average pressure in the cylinders during the power stroke. Higher BMEP indicates better engine design and efficiency.
150-200 PSI
Stock engines: 150-170 PSI
Performance: 180-200 PSI
200-300 PSI
Street turbo: 200-250 PSI
High boost: 250-300 PSI
300-400+ PSI
Top fuel: 400+ PSI
F1 engines: 300-350 PSI
Specific output measures horsepower per liter of displacement. It indicates how efficiently an engine produces power relative to its size. Modern engines achieve higher specific output through advanced technology.
40-60 HP/L
Basic naturally aspirated engines
70-100 HP/L
Advanced naturally aspirated
100-150 HP/L
Modern turbo engines
150-200+ HP/L
Supercars and race engines
Power Increase = Base HP × (Boost PSI / 14.7)
Example: 200 HP engine with 10 PSI boost = 200 × (10/14.7) = 136 HP gain = 336 total HP
First calculate displacement: Displacement (L) = (π × Bore² × Stroke × Cylinders) / 4000 (for mm). Then estimate HP using: HP = Displacement × 50 × Volumetric Efficiency × Pressure Ratio. For a 4-cylinder engine with 86mm bore, 86mm stroke, 85% VE: Displacement = (3.14159 × 86² × 86 × 4) / 4000 = 2.0L. HP = 2.0 × 50 × 0.85 × 1.0 = 85 HP.
BMEP (Brake Mean Effective Pressure) measures engine efficiency independent of size. It represents average cylinder pressure during the power stroke. Higher BMEP indicates better engine design. Typical values: Naturally aspirated: 150-200 PSI, Turbocharged: 200-300 PSI, Race engines: 300-400+ PSI. BMEP = (Torque × 150.8) / Displacement (cubic inches). It's the best metric for comparing different engine designs.
Higher compression ratio increases thermal efficiency and power output. Each point of compression adds approximately 3-4% more power. Example: Increasing from 9:1 to 11:1 adds 6-8% power. However, higher compression requires higher octane fuel to prevent detonation. Typical ratios: Turbo engines: 8:1-9:1, Modern NA: 10:1-11:1, Performance: 11:1-13:1, Race: 13:1-15:1+. Balance compression with fuel quality and boost pressure.
Specific output measures horsepower per liter of displacement, indicating engine efficiency. Formula: Specific Output = HP / Displacement (L). Typical values: Economy engines: 40-60 HP/L, Modern NA: 70-100 HP/L, Turbocharged: 100-150 HP/L, High performance: 150-200+ HP/L. Example: 300 HP from 2.0L engine = 150 HP/L (excellent). Higher specific output indicates advanced technology and efficient design.
Displacement formula: Displacement = (π × Bore² × Stroke × Number of Cylinders) / 4. For metric (mm): divide by 1,000,000 for liters. For imperial (inches): multiply by 0.7854 for cubic inches. Example: 86mm bore, 86mm stroke, 4 cylinders = (3.14159 × 86² × 86 × 4) / 1,000,000 = 2.0L or 122 cubic inches. Displacement directly affects torque and power potential.
VE measures how effectively an engine fills its cylinders with air compared to theoretical maximum. 100% VE = cylinder completely filled at atmospheric pressure. Typical values: Stock engines: 80-85% VE, Performance engines: 85-95% VE, Race engines: 95-100%+ VE (with ram air). Improved by: better intake/exhaust design, variable valve timing, port & polish, forced induction. Higher VE = more air = more power.
Boost pressure depends on engine strength, fuel quality, and tuning. Conservative street: 5-8 PSI (30-50% power gain), Moderate performance: 10-15 PSI (60-100% power gain), High performance: 15-20 PSI (100-130% power gain), Race/drag: 20-30+ PSI (130-200%+ power gain). Lower compression engines handle more boost. Always tune properly and monitor knock. Start low and increase gradually with proper tuning.
Oversquare (Bore > Stroke): Larger bore allows bigger valves and better breathing. Higher RPM capability, more horsepower-focused. Example: 90mm bore × 80mm stroke. Common in performance engines. Undersquare (Bore < Stroke): Longer stroke increases leverage and torque. Better low-end torque, more efficient. Example: 80mm bore × 90mm stroke. Common in diesel and truck engines. Square (Bore = Stroke): Balanced design with good power and torque.
Multiple approaches: 1) Increase displacement: Larger bore/stroke, stroker kit (10-30% gain). 2) Forced induction: Turbo/supercharger (30-150% gain). 3) Higher compression: Better efficiency (3-4% per point). 4) Better breathing: Port & polish, performance heads (5-15% gain). 5) Camshaft: Optimized valve timing (5-15% gain). 6) ECU tuning: Optimize fuel/timing (10-20% gain). Combine modifications for maximum results.
Rod ratio = Connecting Rod Length / Stroke. Typical values: 1.5:1 to 2.0:1. Higher ratio (longer rod): Reduced piston side loading, less friction, better ring seal, smoother operation. Lower ratio (shorter rod): More compact engine, higher rod angle, increased side loading. Optimal ratio: 1.7:1 to 1.9:1 for most applications. Affects piston dwell time at TDC, combustion efficiency, and engine longevity.
Accuracy depends on input quality and engine type. Theoretical calculations: ±10-20% accuracy (estimates based on geometry and efficiency). Best for: Planning builds, comparing configurations, estimating potential. Less accurate for: Highly modified engines, unusual designs, extreme applications. For precise measurements, use chassis dyno testing. Calculator provides reliable estimates for planning and comparison. Actual power depends on many factors: tuning, fuel quality, temperature, altitude.
Piston speed = (Stroke × RPM) / 6 (for inches) or (Stroke × RPM) / 152.4 (for mm). Measures average piston velocity. Limits: Street engines: 3000-4000 ft/min, Performance: 4000-5000 ft/min, Race: 5000-6000+ ft/min. Higher speeds increase stress, wear, and friction. Longer stroke = higher piston speed at same RPM. Limits maximum safe RPM. Example: 86mm stroke at 7000 RPM = 3950 ft/min (safe for performance).