Guys,


I stumbled across a site that has some interesting reading. A partial quote and link follow. http://www.dieselplace.com/forum/smileys/Cool.gif


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.


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............


For more info and equations go to:


http://www.wahiduddin.net/calc/cf.htm

For those unfamiliar with this stuff, I like to point out that commonly published correction factors for normally aspirated engines do not apply to forced induction engines - they overestimate (by about double in my experience and observation with turbo cars) how performance changes with altitude for turbocharged engines. That's still interesting and useful reading, however http://www.dieselplace.com/forum/smileys/Geek.gif. I've bookmarked several such sites http://www.dieselplace.com/forum/smileys/HiHi.gif.


2001 K2500HD, D/A, EC/LB, J/A, LTX265s, waiting for Trippin to market his Attitude bracket, turnover ball, Husky flaps/liners, Permatech sprayed liner


36' Pace Shadow GT GN trailer


1987 Grand National (strip/street) 9.43 @ 143 mph


1987 Grand National (street beater) 11.02 @ 124 mphEdited by: joyof6

Hmm... Same as airplanes.


All aircraft engines and lift/performance numbers are based on a "Standard Day" that is Sea Level, 59 degrees F and barometer 29.92 for the exact comparison reasons the article mentions. Density altitude affects how much lift you get from the wings as well as engine power on an aircraft.


Differences can be expressed as "Densitiy altitude" which is the height above Sea Level, air temp and barometric pressure. There is also a humidity factor.


When my buddy and I were really into the NHRA stuff, I got an old aircraft altimeter which could give us the barometric pressure, and the temp/humidity guages you can buy. Then we figured the desity altitude for the track and jetted accordingly. Everyone, inlcuding my buddy at first, thought I was nuts but it worked well. Now you see equipment in almost all the pit areas to get that info. All that sensing equipment and the computer program he has in his shop allow him to setup engines on the flywheel dyno for where ever they're going to be sent.


It's an important variable for certain activities...http://www.dieselplace.com/forum/smileys/Cool.gif

For those unfamiliar with this stuff, I like to point out that commonly published correction factors for normally aspirated engines do not apply to forced induction engines - they overestimate (by about double in my experience and observation with turbo cars) how performance changes with altitude for turbocharged engines. That's still interesting and useful reading, however http://www.dieselplace.com/forum/smileys/Geek.gif. I've bookmarked several such sites http://www.dieselplace.com/forum/smileys/HiHi.gif.


2001 K2500HD, D/A, EC/LB, J/A, LTX265s, waiting for Trippin to market his Attitude bracket, turnover ball, Husky flaps/liners, Permatech sprayed liner


36' Pace Shadow GT GN trailer


1987 Grand National (strip/street) 9.43 @ 143 mph


1987 Grand National (street beater) 11.02 @ 124 mph





http://www.dieselplace.com/forum/smileys/Big Smile.gif