Results
Estimated torque
312 lb-ft
Estimated horsepower
386 hp
Estimated BMEP
134.4 psi
Formula / model
Pressure ratio = (14.7 + boost) / 14.7, hp = CID x rpm x VE x pressure ratio / 5600, torque = hp x 5252 / rpm, BMEP = 150.8 x torque / CID
This horsepower and torque estimator gives you a fast planning number when you want to compare displacement, boost, rpm, and VE without waiting for dyno time.
Enter your current numbers or target values below, then use the live results to review estimated torque, estimated horsepower, and estimated bmep before you commit to the next parts or setup change.
Horsepower and torque are mathematically linked through engine speed. Torque is rotational force measured in lb-ft. Horsepower is the rate at which that torque is applied over time. The two curves always cross at exactly 5,252 RPM when torque is expressed in lb-ft and power in horsepower.
This estimator uses displacement, volumetric efficiency, RPM, and boost pressure to model output through the pressure-ratio method. The result is a planning-grade number — accurate enough for parts selection and combination comparison, but not a substitute for dynamometer testing.
Brake Mean Effective Pressure (BMEP) is the average pressure acting on the pistons during the power stroke that produces useful work at the crankshaft. BMEP normalizes engine output by displacement — making it possible to compare a 2.0L four-cylinder against a 7.0L V8 on equal terms.
A naturally aspirated gasoline engine producing 130–150 psi BMEP is well-optimized. Values above 200 psi indicate forced induction. Turbocharged production engines reach 300+ psi. The BMEP number reveals how hard the engine is working per unit of displacement regardless of total size.
Volumetric efficiency (VE) measures how completely each cylinder fills with air relative to its theoretical maximum at atmospheric pressure. A stock engine with restrictive intake and exhaust typically achieves 75–85% VE. Ported heads, long-runner intake manifolds, and tuned headers push VE to 90–100%. Ram-air and acoustic tuning effects can exceed 100% at narrow RPM bands even without forced induction.
Interactive — linked to form inputs above
BMEP provides a displacement-independent quality metric. The table below lists validated BMEP ranges for production and performance engine configurations running on gasoline.
| Engine Configuration | BMEP (psi) | Torque per Liter | Context |
|---|---|---|---|
| Stock NA economy | 100 – 125 | ~55 – 70 lb-ft/L | Factory tune, emissions priority |
| Optimized NA street | 130 – 155 | ~72 – 85 lb-ft/L | Ported heads, cam, intake, headers |
| Peak NA race | 155 – 210 | ~85 – 115 lb-ft/L | Pro-stock, ITB, high-compression |
| Mild turbo / supercharged | 180 – 260 | ~100 – 145 lb-ft/L | 6–12 psi street boost |
| High-boost race | 300 – 500+ | ~165 – 275+ lb-ft/L | 20+ psi, race fuel, built internals |
Displacement sets the baseline air charge per cycle. A 350 CID engine at 95% VE ingests 332 cubic inches of air per cycle. A 500 CID engine at the same VE ingests 475 cubic inches — 43% more air and proportionally more fuel, producing roughly 43% more power at identical efficiency.
Each pound of boost above atmospheric pressure (14.7 psi) increases the pressure ratio and the mass of air entering the cylinders. Adding 14.7 psi of boost doubles the pressure ratio from 1.0 to 2.0 — theoretically doubling available power. Real-world gains are lower due to heat, exhaust backpressure, and fuel enrichment requirements.
Horsepower is torque multiplied by RPM divided by 5,252. An engine making 400 lb-ft at 5,000 RPM produces 381 hp. The same 400 lb-ft at 6,500 RPM produces 495 hp — a 30% power increase from RPM alone. The practical RPM ceiling is limited by mean piston speed, valve float, and rod stress.
These are the next calculator pages most likely to be useful once you have this result in hand.
Airflow & Fuel
01Airflow requirement from cubic inches, rpm, and volumetric efficiency.
Airflow & Fuel
02Injector sizing from horsepower, BSFC, cylinders, and duty cycle.
Performance
03Quarter-mile ET and trap speed from power-to-weight.
Understanding the 1971 testing standard shift and how to convert between gross and net HP ratings.
The BMEP-based torque formula and why larger engines produce more torque at lower RPM.
How airflow determines what percentage of your displacement becomes usable horsepower.
It estimates estimated torque, estimated horsepower, and estimated bmep from values such as displacement (cid), boost pressure (psi), and target rpm.
Start with displacement (cid), boost pressure (psi), and target rpm because those are the core values that move estimated torque the most. Then refine the secondary inputs to match the exact combination.
It is a solid planning tool built around the stated formula and assumptions, but final results still depend on real measurements, hardware tolerances, tuning, and operating conditions.
Yes. Change the inputs to reflect your exact parts, operating target, or comparison scenario, then review how the outputs respond before you make the next decision.
A useful next step is to compare the result with Carburetor CFM Calculator, Fuel Injector Size Calculator, and Quarter Mile ET & Trap Speed Calculator so the rest of the combination stays aligned.
