Engine Question

EDIT to post #2
from what I (average-Joe) have gleaned;
It's been said that an engine is "just an air pump". The output of any given engine, regardless of the tune, can be changed just by varying the; temperature, pressure, humidity, etc, of the air going into the engine. The highest output would be with the lowest temp, the lowest humidity, highest pressure; which would then input the maximum amount of oxygen into the engine. If you then take that exact same engine, in the exact same tune, to a new environment, different from the first, then without fail, you will get a different output.
To solve this, the raw data of the dyno, is "corrected" to a standard (STP) that corrects it to what is believed to be normalized at that standard. IIRC that standard is something like; 77*F, @ sealevel and a certain humidity (I forget the number, maybe Zero?), don't quote me.
So after correction, all dynos should,
theoretically, read the same; and consistently from day to day...... even tho the raw data may change somewhat.
In practice, IDK, it seems this is not always the case........ It only takes a minor error in calibrations of the input sensors, or the load-device, to skew even the raw data, and so:
garbage in equals garbage out.
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anecdotal;
>Back in September 1970, I bought me a low-mileage 1970 Swinger 340/4speed/3.55s. During the next couple of years, I got to be very familiar with that engine. It always ran more powerfully as the air got cooler, and lost power in the heat of summer or on high-humidity days.
>In 1975, I got me a brand new Suzuki 750GT "Waterbuffalo". It was rated 70hp. But getting over the Great Divide, in the Rocky Mountains, I had to downshift as the air-density steadily declined.
Back on the Prairies, it was a rocket!........ for 1975, lol.
>I live "on the Prairies" at about 900/930 ft elevation, for at least a 50 mile radius, with minor changes; and I only run my hotrod from May to September, a daytime high temperature variation of not more than 30 degrees, so it's relatively easy to tune my engine.
> tuning snowmobiles tho..... to run from plus a few degreesC, to minus 30/35C* is a tuning range of about 3 jet sizes..... and if you forget to rejet as the temperature falls, well, lets just say I made a lotta money rebuilding melted engines; and the way snowmobiles are run, it only takes a few seconds to kiss a lean-running one goodbye.
> so once again, it's all about getting the oxygen in, and putting just the right amount of fuel, into it.
>And go easy on the ignition timing; on the street, a few degrees short of ideal is safer than a couple too many.
On the dyno; I have watched internet videos in the which the dyno-operators, gained ~7hp going from 2/3 degrees short, to gaining ~2/3hp on the last degree, at the horsepower peak. This on 360 sized engines.
On the street;
at 400hp, that just don't matter to me... lol. My butt-dyno can't tell the difference in output of my 367, anywhere from 32 to 36 degrees, so I just run 32>34* . I mean, a stout 360 will have the tires spinning thru two gears anyway, at least..... and it doesn't take 400hp to do that, not even 350, probably not even 300................ so 7hp, to me, is like, who gibsachit.