Chainsaw Repair

everyone has heard of horsepower and torque.  (kW and Nm for you metric speaking folks).  these published figures have been tossed around for quite some time.  sometimes with heated results.  here are some other ways to compare stock saw motors:

in a nutshell, here is what my chart compares:

***In all cases, the greater number is better.***

BMEP:  Blair says that a value of about 6 at best is all that can be achieved, with a naturally aspirated (non-force induction) motor, with untuned and unmuffled exhaust.   Comparison of motors using pressure values, based on output and actual motor size.

Specific Power:  Considers if each engine being compared was 1000cc in size.  Comparison is made using peak output and torque values at their respective rpm points.

Power to Weight Ratio:  Compares how much kW, to how much the power head weighs.
Power to Torque Ratio:  Compares how much Nm, to how much the power head weighs.

Thermal Efficiency:  % shown, is how much of the fuel being burned, goes to actually spinning the PTO shaft.  (the remainder, of the heat from fuel is lost through the exhaust, engine cooling loss, and internal engine friction).
The % shown in the chart has to little (if anything) to do with fuel consumption, and is not what this chart is showing.


Note:  All results were calculated by me, (except for Specific Power), from data available from kwf testing site.
           Spec Power columns taken directly from kwf. 
           

-joe   

edit:  spent 1/2 hour trying to line up the columns using spacebar on this site.  gave up. sorry. 
          it's lined up when i type it in the "reply" box.


edit#2: added the .txt file attachment where it can be read easier.

edit #3:  above.

updated 08-18-14

stihl ms661 becomes the new power-to-weight king.

(txt file opens immediately on all pc's)

-joe