ENGLISH AND METRIC SPEED EQUIVALENTS To obtain velocity in feet per second multiply the speed in miles per hour by 1.466+ Velocity ft. per sec.= Miles per hour x 1.466+ One mile per hour-1.466 ft. per second=88 ft. per minute=0.447 meters per second-26.8 metres per minute. 1 Km. per hour-0.914 metres per second 54.9 ft. per minute=0.624 mi. per hour. APPROXIMATE HORSEPOWER OF FOUR-CYCLE AUTOMOBILE ENGINES Stroke Table of Constants for Variable Speeds and Strokes REVOLUTIONS PER MINUTE OF MOTOR in Ins. 500 550 600 650 700 750 800 850 900 950 1,000 1,050 1,100 1,150 1,200 2.00..... 0.89.098.107.116.124.134.142.153.161.169.178 .187 .196 .205 2.25. .100.110.120.130.140.151.160.171.181.190 .200 .210 .220 .245 214 .231.241 .257 .268 270 .282 .295 3.50......112.125.133.145.156 .167.176.189.201.212 2.75......123.135.146.159.172.184.196 .208.221.233 245 256 3.00... .134.147.160.174.187.201.214.227.241.254 .267 .279.294 .308 .322 3.25..... .145.158.173.188.203.219.232.246.261.275 .289 .303 .319 .333 .349 3.50.....156 .173.186.203.218.234 .250 .265 .281 .296 .312 .326 .343 3.75 4.00.. 4.25. 4.50.. 4.75 5.00.. -359-375 .167.184 .200 .218.234.252.266.284.301.317 .334 349 .368 .385 .401 .178.196.214.232.249 .268.285.303-321-339 -356 -373 -392 .411 .429 .189.208.227.246.264.285.303-322-341.360 .378 .396 .416 .436 .456 .200.220.240.261.280.305 .321 .341.361 381 .400 .419 441 .461 .485 .212.233.253.275.295.319.339.360.381.402 .223.245.266.290.312 .335-357-379.401.423 423 443.466 .486 .509 445 .466 .491 .512 .536 .490 515 538 .563 5.25.234 .257 .279.304.327 351-375-398.421.444 467 5.50......245 .270 .293.318-343-368-393-417.441.465 .489 513 .540.564.590. 5.75.258.282-307-332.369.385.410.436 461.486.512 .536 .564 .589 .616 .268.294.320.348.375 .402.428.455.481.508 535 559 589 .615 .643 6:00.. Rule:-Multiply number to right of bore by number in upper table at intersection of proper R.P.M. and stroke columns. Example:-Find approximate horsepower developed by motor having 4.25" bore and 5" stroke at 800 revolutions per minute. Under 4.25 bore we find 18.05. At intersection of 5" stroke line and 800 R.P.M. column in upper table we find .357. The product of these numbers gives the horsepower, thus: Approximate norsepower-18:05 X.357-6 45 H.P. These figures have been computed for the average M.E.P. as found in the ordinary motor car engine, but of course will vary with. increase or decrease in compression and with different mechanical efficiencies. For multi-cylinder engines, multiply by number of cylinders. Above formula gives H.P. for only one cylinder. D Diameter of cylinder in inches. L Stroke of piston in inches. lutions per minute of crank shaft. n Number of cylinders. *The above are for automobile racing boat engines; for others the rating is taken as two-thirds of the above formulas. For engines having a displacer cylinder or cylinders the above rating is increased in the ratio that the displacer piston's displacement bears to that of the working cylinders. INDICATED HORSEPOWER On account of the great difficulty of securing good indicator cards at the high-piston and rotative speeds of automobile motors this is very little employed. The manograph which is employed for obtaining cards or diagrams from high-speed motors, as a general thing does not have an equal pressure scale and therefore does not readily lend itself to the accurate determination of I. H. P. The indicated H. P. may of course be determined approximately by assuming a certain mechanical efficiency for the motor under consideration. This varies from as high as 90 per cent. in some cases to lower than 70 per cent. in others; the average would probably be not far from 80 per cent. The formula for I. H. P., the bore and stroke being known as well as the R. P. M. and the mean effective pressure, is, D' X L X R. P. M. × n × M. E. P. = I. H. P. (for 4-cycle). 550,000. This constant equals 550,000 and the formula becomes The constant for 2-cycle is 275,000. A formula which is given by Grover for the mean effective pressure, the compression being known, is as follows: M. E. P. 2C -0.01 C2 C Compression pressure above atmosphere in pounds per square inch. This formula does not hold good for compression pressures over 100 pounds per square inch above atmosphere.. Comparatively recent data seems to prove the reliability of this formula, also the fact, which Grover points out, that under favorable conditions, the values given by this formula may be slightly exceeded. Tests with higher pressures than 100 pounds show that the M. E. P. tends to remain at 100 pounds per square inch. The compression pressure may be obtained by some form of gauge, the ignition for that cylinder being cut off, or in case the volume of the explosion chamber is known it may be obtained from the formula. PV Constant. P being the absolute pressure. V being taken in the one case as the volume of the combustion chamber and in the other as the above plus the piston displacement. P being in one case atmospheric pressure and in the other the absolute compression pressure. Of course for C in Grover's formula the assumed atmospheric pressure should be subtracted from the result ob tained by this formula. |