Horsepower

According to the 330 GT sales brochures, Ferrari claimed 300 HP (English text) or 300 CV (Italian/French text) for the type 209 engine.  Interesting is that a CV (Cavallo-Vapore) is a steam engine unit that is .986 horsepower or about 1.5% less.  Of course, Ferrari was usually optimistic with both top speed and horsepower in order to sell more cars.

The build sheets that Ferrari would supply to customers in the 'old' (pre 1990) days usually had the Prova Al Banco page of the build sheet missing the test numbers.  However, a few years ago, the Ferrari Owner's website offered build sheets to owners who jumped through enough hoops to prove to Ferrari that their car still had the original chassis, engine, transmission and differential.  Those build sheets did contain the test numbers, so I have several sets to work with.

Dan Reese (9119GT) recently had his engine rebuilt and they did a run on an engine dynometer (as opposed to a rolling dynometer where drive line losses occur).  Lowell Brown and I had compared the factory dyno numbers on our 2 cars that were built within a couple of months of each other and my car had slightly better numbers.  However, we never did the math to actually calculate horsepower from the factory numbers.  Here are examples from three cars:

The RPM and serial number fields are self explanatory.  The associated numbers are marked simply as Kg. (Kilograms) on the build sheet.  The Barometric Pressure, Temperature and Humidity fields are used to provide a correction factor so engine testing produces similar results independent of the weather and time of year.  The Measured and Corrected fields are either horsepower or CV.

I asked Lowell if he had ever figured out the formula to convert the Kg. numbers into horsepower and got an answer that if he had, he didn't know where his notes might be.

So Lowell (who is a PHD physicist) came up with the following:
The Prova Al Banco page of Ferrari Build Sheets have a column headed GIRI and an adjacent column headed Kg.
Giri is clearly RPM.
Kg. I assume means a torque of kilogram --- meters. To put this in standard MKS units, one must multiply by the acceleration of gravity: That is Kg. --> Kilogram Meter --> 9.81 Newton Meter = 9.81 Joule
Power (in Watts) is the force (Newtons) times the distance (Meters) traveled per time (Seconds).
At 1,000 RPM with an arm (radius) of 1 meter, the distance traveled per second is 2 pi (1000 / 60) = 2 X 3.1416 X (100 / 6) = 104.7 Meters / Second
With a force of 9.81 Newtons, this gives 104.7 X 9.81 = 1,027 Watts.
There are 746 Watts in one horse power, so 1,000 Giri with 1.000 Kg. = 1,027 / 746 = 1.38 HP
That is, to get the HP from the build sheet, you take the GIRI / 1000 and multiply by the Kg. and then multiply by 1.38.
This gives the British HP. The Italian HP is really a CV = Cavallo-Vapore = steam engine unit = 736 Watts = 0.986 HP

So taking the 1.38 number, the maximum horsepower for the three cars was in the 330-340 range, clearly not right.  If the type 209 engine was developing that horsepower, the sales brochures would have been claiming 350!

I posed this quandary to the Ferrari Historians group and got back an answer from Gerald Roush.  Dyke Ridgley told Gerald that the Kg numbers converted directly to horsepower by simply multiplying by the RPM in thousands.  Here are the new calculations:

As you can see, the calculated horsepower @ 6600 RPM compare almost identically to the Measured numbers above.  You can see that these are down in the 250 horsepower range and now you know why Ferrari didn't include them in the build sheets requested by owners when the cars were new.  Otherwise Ferrari would have to be answering tough questions like 'Why do you advertise 300 HP but only deliver engines making 250-260 HP?' 

Tom Shaughnessy has an original factory dynometer:

   

On the left side of the left picture, one can see a scale the is marked Kg. (not KgM) at the top, along with a place to stack various weights on a holder underneath.  The right picture shows the Ferrari drive shaft with the rubber donut ready to have an engine attached.  In looking at the left picture, one can see an arm coming from the center of the dynometer and terminating under the scale.  This looks to be about 2½' long.  Using the calculated horsepower from Lowell's original formula compared to Dyke's method yields that the KgM should be Kg¾M (actually .728 of a meter), which about the length of the arm.

Here is a graph of the three engines horsepower across the RPM range.

Since Kg. is not a torque value, one cannot fault Lowell for assuming that Ferrari really meant KgM.

As mentioned above, Ferrari tested with an engine dynometer.  Since that requires the engine to be out of the car, today most tuning is done with a rolling dynometer.  There the car drives a set of rollers that the rear wheels run on.  Here are some notes from a rolling dynometer test on a 330 GTC:

Test was done March 2003, numbers are SAE corrected for temp and humidity, but no calculated correction for driveline loss. Numbers are those measured at the wheels on Dynojet Research dynometer.
Max HP – 216.80 @ 6400 - 7100RPM (flat with slight dip at 6900, then peak at 7100 where I let off throttle) Max Torque – 200.93 @ 4800 – 5200 (pretty flat through that RPM range, with gradual decline to throttle lift where it was making about 160 lb/ft)
The car had really good compression was running really well and the air fuel ratio at the exhaust was pretty good, so I don’t think there was much more to be gotten out of it. Everything about the intake and exhaust system was stock correct if not original (all original to my knowledge, but who knows). If you figure a 15% driveline loss, these number work back to about 250HP at the flywheel. I imagine you could argue for days at what the driveline loss calculation should be, so I don’t try to go there. So many variables and no real advantage to the discussion. I always figure the numbers are really only good as comparison when making adjustments to carburetors or timing settings, exhaust system, or whatever, to determine whether you’re really making improvements or not.