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Steel, I like this definition of BMEP:

The definition of BMEP is: the average (mean) pressure which, if imposed on the pistons uniformly from the top to the bottom of each power stroke, would produce the measured (brake) power output.

Note that BMEP is purely theoretical and has nothing to do with actual cylinder pressures. It is simply an effective comparison tool.

If you work through the arithmetic, you find that BMEP is simply a multiple of the torque per cubic inch of displacement. A torque output of 1.0 lb-ft per cubic inch of displacement equals a BMEP of 150.8 psi. in a four-stroke engine and 75.4 psi. in a two-stroke engine.

(The discussion on the remainder of this page is with respect to four-stroke engines, but it applies equally to two strike engines if you simply substitute 75.4 everywhere you see 150.8)

If you know the torque and displacement of an engine, a very practical way to calculate BMEP is:

BMEP = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)

This formula is easier than the above one of:

(HP x 13,000)/(LxRPM) L= liter of displacement.

In reading the definition it real apparent that cam timing would make a huge difference of the BMEP numbers. The same cam set straight up or advanced or retarded could change the number's a bunch.

Or different cam's one for nitrous vs a N/A engine. If the cam opens the exhaust valve earlier (BBDC) it will bleed off energy used it the calc wouldn't it ?

I would also ask, since BSFC is also an idicator of combustion effecancy would an engine have a higher BMEP because it has a lower BSFC ? Do the two go hand in hand ?

I also wounder what the number's would look like on the 565 if the nitrous cam came out and a straight up N/A max power at 7,000 rpm cam went in it.

What produces a higher BMEP, Turbo, blower or Nitrous?

It seem's I have more question's than answer's.

Sleeper CP

Big Inch Ford Lover

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