Brake Mean Effective Pressure, BMEP, What does it mean?

All about your top end :-)
Post Reply
User avatar
Sandblaster
Posts: 6216
Joined: Thu Jun 07, 2012 3:50 pm
Location: Eugene, OR
Contact:

Brake Mean Effective Pressure, BMEP, What does it mean?

Post by Sandblaster » Sat Nov 14, 2020 4:52 pm

Brake Mean Effective Pressure, BMEP, What does it mean?
Because I'm a 2 stroke guy I will be focused on 2 strokes and specifically on the KX500.
Put simply, BMEP is a measurement of the average Pressure exerted on the piston.

Here is a simple formula.

BMEP = 150.8 x Torque in ft/lb / CID
If you know the variables, just plug them in and run the math.
But you need the variables.
I've done a lot of dyno work testing various pipes and reeds so I will use those numbers for examples.
Unfortunately, my numbers are all measured at the rear wheel and not at the crank so I cant filter out the parasitic loss we get through the drive train :(

Here is one sites claim for KX500 output
Max Power 66 hp / @ 7000 rpm
Max Torque 48.4 lb-ft / @ 6000 rpm

On a fresh KX500 2001 KX500 I measured
Max Power 53.11 hp @ 6520 rpm
Max Torque 44.23 lb-ft / @ 6140 rpm
If bikes are for kids I'll never grow up.

User avatar
Sandblaster
Posts: 6216
Joined: Thu Jun 07, 2012 3:50 pm
Location: Eugene, OR
Contact:

Re: Brake Mean Effective Pressure, BMEP, What does it mean?

Post by Sandblaster » Sat Nov 14, 2020 7:12 pm

Lets plug in the claimed numbers to the formula
BMEP = 150.8 x Torque in ft/lb / CID

BMEP = 150.8 x 48.4 ft/lb divided by 30.5119 CID

BMEP = 7,298.72 divided by 30.5119

BMEP = 239.20 PSI
If bikes are for kids I'll never grow up.

User avatar
Sandblaster
Posts: 6216
Joined: Thu Jun 07, 2012 3:50 pm
Location: Eugene, OR
Contact:

Re: Brake Mean Effective Pressure, BMEP, What does it mean?

Post by Sandblaster » Fri Nov 20, 2020 2:49 am

Here is my numbers

BMEP = 150.8 x Torque in ft/lb / CID

BMEP = 150.8 x 44.23 ft/lb divided by 30.5119 CID

BMEP = 218.59 PSI
If bikes are for kids I'll never grow up.

User avatar
Sandblaster
Posts: 6216
Joined: Thu Jun 07, 2012 3:50 pm
Location: Eugene, OR
Contact:

Re: Brake Mean Effective Pressure, BMEP, What does it mean?

Post by Sandblaster » Fri Nov 20, 2020 2:57 am

What can we learn?
Kawi measured at the crank and I measure at the rear wheel :lol:
But there is more.
If bikes are for kids I'll never grow up.

Post Reply

Return to “Top End”

Who is online

Users browsing this forum: No registered users and 1 guest