where did the 70s take the horses
The engines from 71 and earlier are better. Higher compression, less emissions controls.
The emissions controls limited the power. EGR is like eating your own **** - literally, you can't process it twice...
As far as the horsepower ratings, you can't compare them. They were done with different standards. I forgot when, but they also started correcting for altitude and humidity and have a "standard" to adjust for any differences in temperature, humidity, and atmospheric conditions (mile-high in the Rocky Mountains compared to at sea level).
I don't think that the loss through the trans and axle are as high as 75 hp, but do reduce. Also, if you test your engine during the summer and then test it again in the winter, you can correct for the differences in atmospheric conditions.
They also test engine dynos and chassis dynos. The chassis dyno measures what is actually at the rear tires (and eat up your tires while testing).
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Here's some info on dyno testing:
Dyno Correction Factor and Relative Horsepower
So what's all this correction factor stuff anyway??
The horsepower and torque available from a normally aspirated internal combustion engine are dependent upon the density of the air... higher density means more oxygen molecules and more power... lower density means less oxygen and less power.
The relative horsepower, and the dyno correction factor, allow mathematical calculation of the affects of air density on the wide-open-throttle horsepower and torque. The dyno correction factor is simply the mathematical reciprocal of the relative horsepower value.
Originally, all of the major US auto manufacturers were in or around Detroit Michigan, and the dyno reading taken in Detroit were considered to be the standard. However, as the auto industry spread both across the country and around the globe, the auto manufacturers needed a way to correlate the horsepower/torque data taken at those "non-standard" locations with the data taken at the "standard" location. Therefore, the SAE created J1349 in order to convert (or "correct") the dyno data taken, for example, in California or in Tokyo to be comparable to data taken at standard conditions in Detroit.
What's it good for?
One common use of the dyno correction factor is to standardize the horsepower and torque readings, so that the effects of the ambient temperature and pressure are removed from the readings. By using the dyno correction factor, power and torque readings can be directly compared to the readings taken on some other day, or even taken at some other altitude.
That is, the corrected readings are the same as the result that you would get by taking the car (or engine) to a certain temperature controlled, humidity controlled, pressure controlled dyno shop where they measure "standard" power, based on the carefully controlled temperature, humidity and pressure.
If you take your car to the dyno on a cold day at low altitude, it will make a lot of power. And if you take exactly the same car back to the same dyno on a hot day, it will make less power. But if you take the exact same car to the "standard" dyno (where the temperature, humidity and pressure are all carefully controlled) on those different days, it will always make exactly the same power.
Sometimes you may want to know how much power you are really making on that specific day due to the temperature, humidity and pressure on that day; in that case, you should look at the uncorrected power readings.
But when you want to see how much more power you have solely due to the new headers, or the new cam, then you will find that the corrected power is more useful, since it removes the effects of the temperature, humidity and atmospheric pressure and just shows you how much more (or less) power you have than in your previous tests.
There is no "right" answer... it's simply a matter of how you want to use the information.
If you want to know whether you are going to burn up the tranny with too much power on a cool, humid day, then go to the dyno and look at uncorrected power to see how exactly much power you have under these conditions.
But if you want to compare the effects due to modifications, or you want to compare several different cars at different times, then the corrected readings of the "standard" dyno will be more useful.
For actual equations see the article here:
http://wahiduddin.net/calc/cf.htm
Here is a link to SAE J1349:
[ame]http://www.mie.uth.gr/ekp_yliko/SAE_%CE%94%CE%A5%CE%9D%CE%91%CE%9C%CE%9F%CE%9C%CE%95%CE%A4%CE%A1%CE%97%CE%A3%CE%97_%CE%9C%CE%95%CE%9A.pdf[/ame]
