Altitude/Temp General Rule

[Rolo]

http://www.tpub.com/content/construc...s/14050_59.htm

Excerpt:

The effect of ALTITUDE on engine power must also be considered. As a rule, 2 1/2 percent of the output of an engine is lost for every 1,000-foot increase in elevation above sea level. Overheated air entering the cylinders has the same effect on engine power as an increase in altitude. In computing horsepower output, engineers will deduct as much as 1 percent for each 10°F rise in the intake air temperature above a “normal” temperature of 70°F.


Oh no! I am turning into IRPT! lol

[Mike-in-Orange]

quote:The effect of ALTITUDE on engine power must also be considered

That may well be, but if I remember correctly altitude has less of an impact on a turbo engine as it does on a n/a engine. Seems to me that back in the days when Formula 1 was starting to move toward turbo engines (imaging 1.5L engines putting out 1,000BHP!) and the grid was a mix of turbo/non-turbo that the turbo cars had a huge advantage at high altitude tracks. This was due, of course, to the fact that the turbo compresses the air going into the engine (well, duh!) but even though the air density was, of course, equal for all competitors, the compressor effect of the turbo dramatically limited the negative effects.

[Rolo]

Agreed, but I wonder if it takes more spoolage to produce a certain amount of boost; would a higher altitude turbo (compressing thinner air) take longer to produce X lbs. boost than a lower altitude turbo? Would that difference be completely negligible? (I am thinking it would be.)

I am curious, because I live near the "fastest 1/8-mile dragstrip" (lowest altitude) and that could actually be a disadvantage to me against n/a engines.

[JaxPT]

same reason Denver International has such long runways. Where at say 1000' elevation I could get off the ground in a piper cherokee in about 800 ft. It would take 3x that on a nice warm day in denver, less atmospheric pressure. Standard pressure at sea level @ 70 degrees is 14.69 psi whereas in Denver it would be 13.17 psi.
With a turbo I think you still have the advantage, maybe slightly less because if the time/distance involved in a drag race. even though it takes more to spool the same boost, usually higher altitude means cooler temps -2 f per 1000 ft rise in altitude.

which translates to....on a 90 degree day at standard atmospheric pressure a car running at 3000 ft altitude runs like its at 5600 ft altitude.
Now at high altitude on a hot day, ughhhh you'll be turnin some pretty ugly numbers

but just for the helluva it try runnin some density altitude numbers
http://wahiduddin.net/calc/calc_hp_dp.htm

[Rolo]

I thought of that too and wondered how much of that was less power and how much is less aerodynamic lift.

This draws my attention to keeping the air intake from heating up like it does.

[Cal Cruzer]

In WW2 they started using superchargers (turbochargers were referred to as superchargers)on fighters to increase performance. Performance would decrease per altitude compared to a supercharged engine at sea level but as with a NA engine at sea level it would out perferm at altitude. It is all relative to barametric pressure which is your starting point...I think