How to Calculate BMEP

[Tom/CalClassic]

In engineering class the formula for power was PLANk=HP

P=bmep brake mean effective pressure (average pressure for power stroke)
L=stroke
A=piston area
N=revs/min
k=number of cylinders

HP/LANk = P

PLANk

P is for PRESSURE - more specifically, Brake Mean Effective Pressure
(BMEP) which is the average pressure inside the cylinder.

L is for STROKE - the distance the piston moves from bottom to top

A is for AREA - of each cylinder circle -
(bore / 2 * bore / 2 * 3.14 )

N is for RPM - what Gordon said! Double N and HP doubles!
****ALL ELSE BEING EQUAL**** which is very difficult.

k is the number of cylinders

Formula units work out to:

BHP = PLANK / 792,000.

Since L x A x K = the displacement of the engine:

Substitute this into the formula:

BHP = BMEP x Displ. x RPM / 792,000


For the R2800 displacement = 2804 cu in so the formula becomes:

BHP = BMEP x 2804 x RPM / 792,000

Dividing by 2804 over 2804 (= 1) then it becomes:

BHP = BMEP x RPM / 283

So for an example, on a wet takeoff BMEP = 243 and RPM = 2800 so

BHP = 243 x 2800 / 283 = 2404 HP

Rearranging:

BMEP = BHP * 283 / RPM

At 2400 HP and 2800 RPM BMEP = 2400 * 283 / 2800 = 243

Hope this helps,