RE: bmep (was:Top Gear: The TT article)

[Eaton Dave <dave.eaton@minedu.govt.nz>]

no avi, i disagree.  bmep is a measure of efficiency, not of stress.  it
can, of course, equate to stress in the same way that simple rpm can.  the
higher the rpm, the higher the stress.  however, chris' clarification is
correct in that there are other, much more specific measures for stress
available.  piston speeds being most commonly used.

semantics?  no, not really.  agree with your final conclusion though.  but
as i said substitue rpm for bmep and it would also be true...

remember that bmep is not (as chris assumes i think) a single number for a
particular engine.  it varies under any number of situations.  clearly
engine speed is one.  but so is fuel.  remember that efficiency is basically
the ability of the engine to extract the most from a particular unit
(quantity) of fuel.

so, more correct is the measure of the fuel consumption *against* the bmep
*and* engine speed co-ordinates.  the result is a "contour plot" showing
lines of bmep against engine speed for varying values of fuel consumption
(actually brake specific fuel consumption - bsfc - which is the volume by
weight of fuel used by an engine to produce one kilowatt for one hour).  

still, i'm sure that there are people on the list more qualified than i am
to comment further.

dave
'95 rs2
'90 ur-q

On Thursday, October 08, 1998 4:41 PM, Avi Meron [SMTP:avi@cosmoslink.net]
wrote:
> Dave,
> The higher the BMEP the higher the stress on the engine.........what
testing
> does is determine what is a safe BMEP to run an engine at (exclude racing,
> too much on the edge!), after the basic calculation is established. It is
> correct to assume that if the BMEP is lower, the stress on the engine is
> LESS....
> Avi