Just asking if someone can confirm the horsepower ratings for the T please
The Bible lists it as 22HP (4.5:1 compression ratio)
Then after 1912 it drops to 20hp (4.1:1)
Would it still be 20HP after 1916 when the 3.98:1 ratio was introduced?
It also mentions a NACC HP rating of 22.5. What is the NACC? Is it todays SAE ??
I'm confused how these de rating changes where achieved apart from the introduction of the "High head" Thanks. Alan
NACC stands for National Automobile Chamber of Commerce (1913-1934).
The standard horse-power rating, formerly known as the A. L. A. M. Rating, has been officially adopted by the National Automobile Chamber of Commerce, Inc.
The formula adopted is
D*D x N/2.5
D is the cylinder bore in inches, N the number of cylinders, and 2.5 a constant, based on the average view of eminent engineers as to a fair, conservative rating for a four-cycle motor at one thousand feet per minute piston speed. (http://what-when-how.com/cars/n-a-c-c-horse-power-rating-car/)
I can fairly easily understand what horsepower is. I struggle with understanding how it is determined. For example, in the data contained in the link posted by George, taken into account are bore, number of cylinders, and a "constant". Wouldn't stroke have a significant effect? Why isn't it a factor? Also, it completely ignores aspiration (carburetion, number and size of valves, cam duration) which, as we all know, can significantly effect engine power.
The early "horse power" figures were for vehicle or road tax purpose. There is an opinion that in the early years of automobile design the taxable horsepower was close to the actual power being produced by an engine.
Explanation of horse power tax:
Chart showing taxable horsepower of modern vehicles:
Enjoyable road tax explanation:
With tweaking horsepower of any internal combustion engine can be raised above the NACC value.
No matter what the official HP is in the books (about 20), that doesn't necessarily apply to actual cars being driven in the real world. Dynamometer tests at an MFTFCI meet were published in the Model T Times. They ranged from under 10 to over 40, depending on condition and modifications. Even on strictly stock cars, there was quite a range of results.
Jeff, your are correct about hp output. The early cars, before there was an horsepower race, were rated by the taxable or NACC value. What was considered as the HP output of the an engine was acceptable. And the road or horsepower tax was not out of line for automobile owner of any social status. You could by a high price vehicle as a Packard or Knight with the same taxable 20 HP as the T. As engine design improved including overhead valves and relocation of cam shafts, increased compression, "hotter" fuel, improved fuel delivery, lighter material and "second star to the right and straight on 'til morning" engineering horsepower got muddled.