190SL Horsepower 

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Determine your car's horsepower:

The graph at left was created by an Excel spreadsheet program that converts an automobile's acceleration times into horsepower and torque.  

You can download the program by clicking here ; you must have the Microsoft Excel on you computer.  Collecting the data for the program requires a stopwatch which will record an save at least eight "split" times, an understanding of the accuracy of your speedometer and a good estimate of the total weight of your car at the time of the test (including driver and passenger). 

When you first download the program, it will probably open an Excel window, save save the program to disk.  If it doesn't open a new window, save the downloaded file to disk and open it using Excel.  The data contained in the spreadsheet are from my tests with my 1961 190SL so you can use that as a starting point in understanding how the program works.  Like all programs, the accuracy of the results is dependant on the accuracy of the data that you enter, the more accurate the data gathered, the more accurate the horsepower estimates.  Page through the program and look at the data input areas.  You can blank out the fields on the data input page and print it for data collection use. 

The first data item is the total weight of the car, fuel, driver and passenger.  I estimated this from a base weight of the car of 2,510 Lbs and added the weight of  myself and my son.  A better approach is to visit a truck stop and have your vehicle weighed.

The next item needed is an accurate mapping of actual speed (in MPH) to the engine RPM.  I just read my speed (adjusted from Kilometers to MPH) for the specific tachometer points of 1500, 2500, 3500, 4500 and 5500 RPM's in third gear.  A better method of determining speed is the use of a handheld GPS receiver which is far more accurate than our old speedometers.

The program requires the collection of both acceleration times in third gear and deceleration times with the car out of gear.   Begin the acceleration run in third gear below 1500 RPM; accelerate at full throttle, calling out "mark" points to your navigator at each tachometer point up to 5500 RPM (about 70 MPH), record the times on a worksheet.  The deceleration times are a little more interesting to record.  Begin by accelerating to a speed greater than the speed at 5500 RPM in third gear.  Put the car in neutral and begin coasting, calling out "mark" at each speed that corresponds to the engine RPM's that was recorded during acceleration.  I had my navigator tell me the speed he wanted after each "mark" I reported.   

One more note on using the program.  The speed verses RPM graph was included so that you could map a speedometer calibration error.  While I didn't use it, you need to enter the speed values to be utilized in the program for the RPM values in cells C 112 through C 120.  For engineer types, the program uses the factor of 80% to convert rear wheel horsepower to flywheel horsepower.  This is a factor that I got from the ""dyno guy" that ran Robby and my cars on the dyno.  The original spreadsheet utilized deceleration in gear to calculate flywheel horsepower.  I technically disagreed with the method so I just utilized the factor.  Regardless of actual accuracy, the program is very good at showing differences between runs and cars.

Give the program a "run".  It is interesting and can provide a baseline to evaluate various tuning conditions.  I doubt that may other 190SL's run my 45 degree ignition advance at 3000RPM; but experiment.  Post your experiences and results on the Forum. 


Any problems or questions from the above, post it on the Forum or email to Jim Villers