How does temperature and altitude effect my V10's power output?

Compiled by: Dave Adkins, resident Viper Techno-nerd and member of the Viper Club of America Pacific Northwest Region

I lived in Florida for ten years, so I know what hot is. One thing I noticed at the Gainesville Raceway drag strip was that my ETís would get better as the air became cooler. At 2:00 pm, Iíd be running consistent 13.92s (not in a Viper), but at 7:00 pm during eliminations, I would somehow manage to run below my dial-in and see 13.78 on my time slip. And not bring home any trophies :-(

You donít have to be a chemist to know that temperature and altitude affect air density (as well as humidity). I dusted off my old Fluid Mechanics textbook and looked up air density tables based on both temperature and elevation above sea level..

Temperature first. Ever noticed that your GTS has more oomph at 5:00 am on your way to work compared to the 3:00pm ride home? Those Spring mornings can be a chilly 40 degrees F. Chrysler rates the horsepower number of 450 hp at a sea level altitude and an air inlet temperature of around 70 degrees. However, that same motor can be making 480hp on those chilly mornings, just due to increased air density. The colder the air, the denser it is.

The graph below illustrates how hot or cold air affects your V10ís power output. You can see the reference point of 450 hp at 70 degrees. This is not a straight line because of the viscosity changes of the air. The colder the air is, the more viscous it becomes, and hence is a little more resistant to flow around bends (intake runners, etc) and such.

Hmmm...this graph is based on the simple physics of air density as a function of temperature, but Dynojet's rule of thumb is that a 1% increase in power occurs for every 10 degrees F cooler, which doesn't agree with this graph, does it? At 20 degrees F, power output should be around 475 hp, not 500 hp. Maybe I better go back and check a few more things out.

So, how bad of a hit is your new RT/10 taking in the horsepower department because you live in Denver, Colorado (a mile above sea level)? Would you believe youíre down 80 horsepower? Believe it. The air is 17% less dense, hence a 17% power loss. If you know your hometownís elevation, you can look up the corresponding power difference using the below graph:

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