Recently there has been much banter about dyno numbers and what could and couldn't be relative to corrected numbers. As a suggestion on a place to at least get started and even help out if you want to learn some things.The following website is offered as a start on learning about the effects of weather on an internal combustion engine and other things:
Some caveats need to be offered as well. When the calculator asks for a barometer reading the number to use there is a "corrected" barometer reading. It is worthy to note the number the local weather guy or gal uses is corrected to a sea-level standard. Where I live it is common to use at least 6.20"Hg addition to whatever you might see on a manifold pressure gauge to get to the sea-level equivalent.
Of course I live at a location that is up in the air a bit.
I suggest to you that you can follow the weather at Bandimere Raceway this weekend during the Mile High Nationals to see how the density altitude shifts and swings. Also note that many of the engines in racecars would have been developed and tested at much lower altitudes and drastically different conditions.
This is just a beginning so I hope that each of you that might be interested in this stuff will start to appreciate that numbers mean something only if you know where the numbers come from.
An ideal circumstance would be indeed to dyno test and collect numbers at exactly the same conditions as one would apply the engine to, but reality quite often overcomes ideal. Also, as you well know the swing in weather conditions and their effects are pretty drastic at a place like Bandimere.
It is most telling when folks come from sea-level (or close to it) conditions and run up here on the mountain and get the shock of their lives.
That is very evident when folks come up and race at Pikes Peak Hillclimb where the starting line is at 9000' and the finish line is at 14110'
Folks that test and develop their stuff at very low altitudes and overall good weather conditions can miss a combination a substantial amount and not even know it because the excess oxygen conditions is very forgiving. That is particularly true when they choose wheezy camshafts (valve timing events). Up here where the air is "thin" we become a bit more cognizant of how important those events are.
Harold, a perfect example would be to take a look at the pro stocks, they will be down 14.7 MPH at Denver this weekend, now Im sure you know how much power a pro stocker makes, how much HP is 14.7 MPH in a pro stock?
Can't remember but I think you loose apox. 2-3% for every 1000-1500' you go up, all ather things being the same.
Years ago at the Cougar Reunions in Salmon Arm B.C. were a few regulars from Washington that ran around sea level, Salmon Arm is 1500'. these guys ran cleavers on their tunnels, where locals ran chopper or ET's. Most of them would loose 6-8mph, due to hp loss and the thinner air not providing as much lift to the hull, water is harder at lower alt as well.
So hp is not the only thing altitude hinders, very noticable with tunnel hulls.
Last sessions of the day with DA at 8462' that is a swing of 646' or more in one racing day - Try and stay on top of the tune-up without paying attention to the weather and you will be whistling Dixie!
Today started with a DA reading of 7384' at 0900 and it finished with a track reported DA of 8759'. That is a pretty big swing of 1375'. Just enough to cause a crew chief or tuner dude to pull hair out.
The final qualification of the ProStock field sees less than about 20+Hp difference on the first 8-10 cars.
Tomorrow is another day and the tuners will have to chase the weather again in the heads-up bash.
Ok, that is the last of the weather words and results for a while. It would have been more fun if there had been some give and take about the effects.
Maybe those that could were out floating their boats and enjoying the weekend.