Engine BMEP (Brake Mean Effective Pressure)
Torque normalized by displacement, so engines of any size compare directly on how hard each cycle works.
Example
You enter
- Peak torque (lb-ft) 400
- Displacement (cubic inches) 350
- Engine cycle four_stroke
You get
- BMEP 172.3 psi (11.9 bar)
Checked against published worked examples from: EPI Inc.
Details, formula, and sources
ScopeBMEP = 150.8 x torque(lb-ft) / displacement(CID) for a 4-stroke (75.4 for a 2-stroke). A 350 CID V8 at 400 lb-ft runs 172 psi -- squarely in the healthy naturally-aspirated gasoline range. NA gas engines top out near 180-190 psi because they fill on one atmosphere, so a BMEP above that is the signature of boost, and a low value points to a mild cam, a restriction, or wear. Evaluated at the torque peak from a corrected dyno pull. A comparison metric, not a design limit; the dyno sheet governs.
Formula or tableBMEP(psi) = 150.8 x torque(lb-ft) / displacement(CID) for a 4-stroke (75.4 for a 2-stroke); from BMEP = 2*pi*n_rev*T/V_d with T in lb-in and V_d in in^3.
Source and editionBrake mean effective pressure (SAE; Heywood, Internal Combustion Engine Fundamentals), by name; the engine and its dyno sheet govern.
Free accessBMEP's definition (work per displacement per cycle) is standard engine theory; the torque and displacement come from the dyno sheet and the engine spec.
What governsEstimate. AHJ and licensed professional govern.
API field namestorque_lb_ft, displacement_cid, cycle_type, bmep_psi
- Cycle factor 150.8 for a 4-stroke (fires every 2 crank revs), 75.4 for a 2-stroke (every rev)engine theory
- Evaluated at torque peak BMEP is taken at the rpm of maximum torque, using a standard-day corrected dyno figureSAE J1349 practice