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Horsepower calculator: torque, rpm and quarter-mile

Horsepower from torque and rpm (hp = lb-ft × rpm ÷ 5252) or from quarter-mile ET and trap speed, with crank vs wheel horsepower and drivetrain loss.

تازہ کاری جانچی گئی مثالیں: 9

rpm
%
Share of crank power lost before the wheels. Garrett Motion's rule of thumb: 10% FWD, 15% RWD, 20% AWD, more with an automatic.
آزمائیں
میکانیکی ہارس پاور
hp
میکانیکی ہارس پاور: 373.2 hp
اعشاری مقامات: 1؛ قریب ترین؛ برابر فاصلے پر جفت ہندسے کی طرف
طاقت
278.3kW
Metric horsepower
378.4PS
ٹارک
350.0lb-ft / 474.5N·m
Crank horsepower
373.2hp
Wheel horsepower
317.2hp

350 lb-ft (474.5 N·m) at 5,600 rpm is 373.2 hp, 278.3 kW or 378.4 PS; with a 15% drivetrain loss about 317 hp reaches the wheels.

Power at a constant torque

020040002,0004,0006,0008,000Engine speed (rpm)hp and lb-ft373 hp at 5,600 rpm5,252 rpm
Torque 350 lb-ftHorsepower
حساب کا طریقہ S

  1. Horsepower from torque

    hp=350.00 lb-ft×5,600 rpm5252.11=373.18\text{hp} = \frac{350.00\ \text{lb-ft} \times 5{,}600\ \text{rpm}}{5252.11} = 373.18

    5252.11 = 33,000 ft·lbf/min ÷ 2π; the calculator uses 2π exactly.

  2. کلوواٹ

    kW=474.54 N⋅m×5,600 rpm9549.30=278.28\text{kW} = \frac{474.54\ \text{N·m} \times 5{,}600\ \text{rpm}}{9549.30} = 278.28

    9549.30 = 60,000 ÷ 2π.

  3. Wheel horsepower after drivetrain loss

    373.18×(1−0.15)=317.21 hp373.18 \times (1 - 0.15) = 317.21\ \text{hp}

    Real losses are partly fixed and partly proportional, so a single percentage is an approximation.

Horsepower calculator: torque, rpm and quarter-mile کے بارے میں

Power is torque times rotational speed. In US units that is horsepower = torque (lb-ft) × rpm ÷ 5,252, where 5,252 is 33,000 ft·lbf per minute divided by 2π; in metric units kW = torque (N·m) × rpm ÷ 9,549. The calculator also runs the formula backwards to get torque from a power figure, and shows the result in hp, kW and metric PS.

From a drag strip time slip it estimates engine horsepower with four published empirical formulas that link race weight, power and the quarter mile: Hale, Huntington, Fox and Jeff Lucius's best fit to 243 Road & Track tests. A 3,500 lb car trapping at 105 mph works out to about 316 hp by Hale's trap-speed formula and 324 hp by the Lucius fit.

Quarter-mile figures are estimates: traction, gearing, weather and the driver all move the time slip. Trap speed tracks power more closely than elapsed time. Wheel and crank horsepower differ by the drivetrain loss, entered here as a percentage.

حل شدہ مثالیں

350 lb-ft at 5,600 rpm

Calculate
From torque
ٹارک
350 lbf·ft
Engine speed
5600 rpm
The torque or power figure is
At the crank (engine)
Drivetrain loss
15%
میکانیکی ہارس پاور
373.2 hp
طاقت
278.3 kW
Metric horsepower
378.4 PS
ٹارک
474.5 N·m
Wheel horsepower
317.2 hp

جانچ کا ماخذ: ⁨Python decimal with 2π exact: 350 × 5600 × 2π / 33000 = 373.183 hp (Inch Calculator's worked example gives 373.19 with the rounded 5,252); × 0.85 = 317.206⁩

400 N·m at 3,000 rpm

Calculate
From torque
ٹارک
400 N·m
Engine speed
3000 rpm
The torque or power figure is
At the crank (engine)
Drivetrain loss
15%
طاقت
125.7 kW
میکانیکی ہارس پاور
168.5 hp

جانچ کا ماخذ: ⁨Python decimal: 400 × 3000 × 2π / 60000 = 125.6637 kW; ÷ 0.74569987 = 168.5178 hp⁩

Torque from 300 PS at 6,000 rpm

Calculate
Torque from hp
طاقت
300 PS
Engine speed
6000 rpm
The torque or power figure is
At the crank (engine)
Drivetrain loss
15%
میکانیکی ہارس پاور
295.9 hp
ٹارک
351.2 N·m
ٹارک
259.0 lb-ft

جانچ کا ماخذ: ⁨Python decimal: 300 × 735.49875 W = 220,649.6 W; ÷ (6000 × 2π/60) = 351.175 N·m = 259.013 lb-ft⁩

Edge: 300 hp measured at the wheels, 15% loss

Calculate
Torque from hp
طاقت
300 hp
Engine speed
6000 rpm
The torque or power figure is
At the wheels (chassis dyno)
Drivetrain loss
15%
Wheel horsepower
300.0 hp
Crank horsepower
352.9 hp

جانچ کا ماخذ: ⁨Hand calculation: crank = 300 ÷ (1 − 0.15) = 352.941 hp⁩

سوالات

How do you convert torque to horsepower?

Multiply torque in lb-ft by rpm and divide by 5,252. An engine making 350 lb-ft at 5,600 rpm produces 350 × 5,600 ÷ 5,252 = 373 hp. The constant comes from James Watt's horsepower of 33,000 foot-pounds per minute: a 1 lb-ft torque does 2π foot-pounds of work per revolution, and 33,000 ÷ 2π = 5,252.1. In metric units, kW = N·m × rpm ÷ 9,549.

Why do horsepower and torque curves cross at 5,252 rpm?

At 5,252.1 rpm the conversion factor is exactly 1, so the number of horsepower equals the number of lb-ft. Below that speed the torque figure is larger, and above it the horsepower figure is larger. On a dyno chart drawn in hp and lb-ft on the same scale, the two curves always meet at 5,252 rpm; drawn in kW and N·m they cross at 9,549 rpm instead.

How do you estimate horsepower from a quarter-mile time?

Hale's formulas give hp = weight × (trap mph ÷ 234)³ or hp = weight ÷ (ET ÷ 5.825)³, with weight in pounds including the driver. A 3,500 lb car trapping at 105 mph comes out at 3,500 × (105 ÷ 234)³ = 316 hp. Jeff Lucius's comparison of 243 Road & Track tests found trap speed predicts power better than ET, because launch and traction affect the time far more than the speed.

What is the difference between wheel and crank horsepower?

Crank (brake) horsepower is measured at the engine's output shaft; wheel horsepower is what reaches the tires on a chassis dynamometer after the transmission, driveshaft and differential take their share. Garrett Motion's rule of thumb is a 10% loss for front-wheel drive, 15% for rear-wheel drive and 20% for all-wheel drive. Road & Track measured a 500 hp Mustang at 421 to 465 wheel hp on four different dynos.

What is the difference between hp, PS and kW?

Mechanical horsepower is 550 ft·lbf per second, or 745.7 watts (NIST SP 811). Metric horsepower (PS, CV or ch) is 75 kgf·m per second, 735.5 watts, so 1 hp = 1.0139 PS. European makers quote PS or kW: 300 PS is 296 hp or 220.6 kW. Electric horsepower, used for motors, is defined as exactly 746 watts.

“⁨Horsepower calculator: torque, rpm and quarter-mile⁩” کتنا درست ہے؟

درستی آپ کی درج کردہ قدروں اور طریقے کے مفروضوں پر منحصر ہے۔ اعشاری حساب 50 بامعنی ہندسے استعمال کرتا ہے، مگر تخمینے، عددی طریقے اور ماخذ کا ڈیٹا کم درست ہو سکتے ہیں؛ دکھائی گئی قدروں کو راؤنڈ کرنے سے یہ حدود ختم نہیں ہوتیں۔ آزاد ذرائع کی حل شدہ مثالوں سے جانچ: 9۔ مثلاً، “⁨350 lb-ft at 5,600 rpm⁩” کو ⁨Python decimal with 2π exact: 350 × 5600 × 2π / 33000 = 373.183 hp (Inch Calculator's worked example gives 373.19 with the rounded 5,252); × 0.85 = 317.206⁩ سے جانچا جاتا ہے۔

اس طریقے کا ماخذ کیا ہے؟

NIST SP 811 Appendix B.8 — horsepower (550 ft·lbf/s) = 745.6999 W; metric horsepower = 735.4988 W; Jeff Lucius, stealth316.com — Calculate horsepower, ET and MPH (Huntington, Fox, Hale and LRT formulas with fit to 243 Road & Track tests); G. T. Fox, “On the physics of drag racing”, American Journal of Physics 41, 311 (1973); Garrett Motion — Crank vs wheel horsepower (drivetrain loss rule of thumb).

اس کیلکولیٹر کے بارے میں

hp=τlb-ft×rpm5252,kW=τN⋅m×rpm9549,hpHale=W(mph234)3\text{hp} = \frac{\tau_{\text{lb-ft}} \times \text{rpm}}{5252},\qquad \text{kW} = \frac{\tau_{\text{N·m}} \times \text{rpm}}{9549},\qquad \text{hp}_{\text{Hale}} = W\left(\frac{\text{mph}}{234}\right)^{3}

ماخذ

  1. NIST SP 811 Appendix B.8 — horsepower (550 ft·lbf/s) = 745.6999 W; metric horsepower = 735.4988 W
  2. Jeff Lucius, stealth316.com — Calculate horsepower, ET and MPH (Huntington, Fox, Hale and LRT formulas with fit to 243 Road & Track tests)
  3. G. T. Fox, “On the physics of drag racing”, American Journal of Physics 41, 311 (1973)
  4. Garrett Motion — Crank vs wheel horsepower (drivetrain loss rule of thumb)

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