<VV> Actual vs. advertised hp

[Tony Underwood]

At 09:11 hours 03/10/2005, NicolCS at aol.com wrote:
>Boys, boys, boys.  Can't we all just get along? <ggg>


No.  I wanna  kill.   Kill!   KILL!


>"Measured hp" depends on the specified test conditions. In the early days 
>they tested "Gross hp" which was the actual output before loads and losses.


This did leave the consumer with a pretty good idea of what the engine 
itself was good for.   However, such tests did tend to be subjective, with 
too many variables to deal with once they began using NET ratings, what 
with some engine applications having much less "work" to do under the hood 
and thus would still make some larger numbers, rendering any set formula 
less than accurate.


>In '72 the switched to "net hp" which was the output after loads and 
>losses.  Both were accurate in the specified test condions. What's the big 
>deal?

In the instance which has proven so amusing and entertaining, the question 
was whether the specs used to describe engine performance were indeed 
accurate.   Since there were at least two different over-all sets of 
specifications, it leaves a bit to be desired as to whether the debate over 
different engines' performances were measured with the NET specs or the 
Gross specs...  something which has never been made quite clear.



>FWIW, you can usually get pretty close to "net" by multiplying "gross time .7)


...to a point.   Smaller engines suffer more than larger 
engines.   Accessory losses like fan, water pump, transmission drag etc 
would be considerably more for an engine like, for instance, a 2xbbl 
carb'ed 318 V8 compared to a 440 3x2bbl variant which would be hauling the 
same underhood accessories and fan and transmission etc.   The 318 will 
suffer a larger net (no pun) loss overall than the 440 would.   Spin the 
accessories and gearbox at 4800 rpm and they require, for sake of argument 
(and according to the Chrysler Direct Connection sorts), ~35 hp on 
average.    The 235 hp 318 might drop from 235 to 200... while the .7 
factor would make it around 165hp.   meanwhile, that same 35 hp drag would 
take the 440x6 from 390hp to 355hp and that .7 average denominator would 
drag the 440 down to 273 hp...  when both engines were pulling the same 
accessories, same fan, same gearbox, etc.    So, the rule of thumb doesn't 
always work in many instances when you're dealing with a wide variety of 
engine applications...  but it can get close when the playing field is 
leveled a bit.

In late '71, Chrysler rerated the 390hp 440 down to 330 hp and the 318 to 
185 hp.   This included the automatic transmissions which most of the 
engines were being supplied with at the time, made sense seeing as how the 
Torqueflite is not a frictionless transmission by any means, especially at 
higher rpm.

So, for sake of yet another debate, your .7 figure is a tad bit severe, for 
the EARLY 1970s when NET began rearing its head.   However, the 
manufacturers weren't terribly concerned about accuracy at the time and 
after smog and demands for running on regular, and subsequent compression 
drops came along, it's likely that the .7 factor would figure fairly close 
in formula-rerating a '60s performance type engine as compared to its 
smoggy degraded descendents of the mid-70s.

It sure would take a bite out of a Corvair dyno chart.




tony..