FARM MOTORS 367 



ability of the engine to carry a full load without any over- 

 heating of the bearings, or other disorders. 



Estimating Horsepower. The horsepower of a gasoline 

 engine may be estimated from the diameter of the cylinder, 

 the length of stroke, and the revolutions per minute. If these 

 quantities are known for several engines, a comparison of their 

 horsepower may be made. Such an estimate can only be 

 considered approximate, however. 



A satisfactory formula for estimating the horsepower of 

 gasoline engines of the four-stroke cycle type is as follows : 



D 2 L R* 

 B.H.P. = - 



18,000 



where D = diameter of cylinder in inches. 

 L = length of stroke in inches. 

 R = revolutions per minute. 



For two-stroke cycle engines the formula should read as 

 follows : 



D 2 LR 

 B.H.P. = - 



13,600 



Another formula which has been suggested for vertical 

 tractor engines is: 



66 D 2 L Rf 



B.H.P. = 



1,000,000 



For horizontal engines the formula is made to read as 

 follows : 



75 D 2 L R 



B.H.P. = 



1,000,000 



These formulas will agree very closely with the brake 

 horsepower of tractor engines developed in public test. 



*E. W. Roberts. 

 fW. F. MacGregor. 



