HP vs. elevation

[pugmire]

I found a horsepower as a function of elevation calculator on this website:

http://murray.faithweb.com/formulas.htm

It claims that my stock 305 ponies from the factory equals 238 at 7285 ft elevation (the elevation where I live). Does this big of a loss make sense? And out of curiosity, would cars that are not NA be so adversely effected?

[Flash 97 WS/6]

I'm not sure about the accuracy of that but it sounds about right to me... operating an engine in high altitude "thin air" is exactly the opposite of supercharging the engine. Fewer molecules of oxygen per sq. inch going in means less power being generated.

A supercharged (or turbo) engine will suffer a similar (although I believe SLIGHTLY less) power loss, the thing is that super and especially turbochargers can just be adjusted to compensate for the altitude. For example, a 5 psi turbo is actually 5 psi above ambient pressure, so at sea level pressure of about 14.7 psi, you add the 5 and are running the engine at 19.7 psi of intake pressure. Now, take the same car at 5000 feet (I have no idea here, just making up a number) the air ambient pressure might be 11.7 psi... 11.7 + 5 means 16.7 psi total at the intake... change the blower pulley or adjust the turbo wastegate to deliver 8 psi and you have 11.7 + 8 = 19.7 psi at the intake, the same as the sea level engine and it will make the same power minus the extra parasitic loss of spinning the blower faster.

Now, what was the question again??

Basically yes the non NA car will affected the same but can compensate more easily than a NA car.

[Craig 94 TA GT]

Just for reference...the Pro Stock class (NA 500 CID V8) loses about 15 mph at 5000 ft. The top fuelers lose 20 or so mph. Since 15 / 205 is about 7.3%, and 20 / 330 is about 6.1%, this shows Flash to be right on the money

[fastTa]

Math is like, like....... cool and stuff!

[Injuneer]

"standard" air pressure at 5,000-feet is generally taken as 24.89"Hg, or about 12.23psia.

If you simply proportion HP to absolute pressure, you get slightly lower net HP than the table shows.... about 5HP lower at 5,000-feet for the 305HP example.

N2O - throttle in a bottle.... unaffected by altitude A 200-shot it sea level is a 200-shot at 7,285-feet. (you do need to be careful of the higher resulting O2 concentration and its affect on burn speed.)

[TrAnS Am 98]

wow thats fun haha
i think i still wanna go to the track tho

[Craig 94 TA GT]

lol

I just threw out estimated numbers in my post...some pretty sloppy math lol
I guess that's the difference between a scientist and an engineer...remember Fred's post a while back?
Which one would you prefer to be? I think I could attempt to become a scientist, but don't think I could take the constant preciseness, and not use good ol common sense!

[Injuneer]

I have a table in my online ScanMaster writeup that has the standard barometer numbers that I copied from (as I recall) the "Chemical Engineer's Handbook".

ELEV - - - STD BAR
Feet - - - - "Hg
0 - - - - - 29.92
1,000 - - - 28.86
2,000 - - - 27.82
3,000 - - - 26.81
4,000 - - - 25.84
5,000 - - - 24.89
6,000 - - - 23.98

You can also go to a site and find the NHRA altitude correction factors ("Stock"/"Super Stock" classes) that allow you to convert your actual performance at a higher elevation to an equivalent ET and MPH at sea level (actually, they correct to 230-240-ft elevation).

NHRA Altitude Correction Factors

[alenstein]

Aviation is where turbo charging originated, as aircraft technology progressively increased so did the ablility for aircraft to fly at higher altittude to compensate for the loss of atmosphereric pressure at higher altittude the airplanes had to get boosted, plus u had to pressurize the cabin otherwise you would pass out. Not much of a boost in the early days 2-5 psi just to achieve the sea level prssure. Being a A&P (aicraft and poweplant) student I couldntt resist to share my knowledge..hehe Every innovation on cars was addapted from aviation. My 2 pannies.