Christos

Ok, lets say we have a 500 HP Camaro, which has a supercharger, pushing 9 pounds of boost to reach this HP level at sea level.

Now, if we take this same Camaro up to Denver, (Mile high) wouldn't it produce the same 500 horsepower, providing that the boost level stayed at 9 PSI?

I am asking this because my friend has a 35th anny SS Camaro, and the HP Numbers were very low uncorrected for the altitude up here. I think it was pushing about 100 HP Less due to altitude. The engine is stock, and N/A.

In theory, if boost levels stay the same in a boosted application, does altitude matter? Wouldn't say 9 PSI of boost produce the same amount of power here, or at sea level? I would think so, but I am hoping somebody could fill me in. I know I would like to get a blower/turbo for my camaro at some point, but I was curious if I still expect to see less power by living at this altitude.

Thanks!

a73camaro

More so then not, the answer to your question.

Sorry for the vagueness, but there is an explanation for this. For boost, 9 PSIg is measured with a gauge, or relative to ambient conditions. At sea level there is 14.7 PSIa ABSOLUTE air pressure. In Denver there is 12.1 PSIa ABSOLUTE air pressure.

One would have to increase boost pressure 2.6 PSI more for a total of 11.6 PSIg. So no biggie, turn up the boost to regain lost power, BUT it costs more engine power to make the higher boost, so some of the increase is lost.

Christos

I wasn't thinking of the base atmospheric pressure coming into play for final boost numbers!

Thanks for the reply, actually, I understand things much better now!

I would assume using a turbo to boost pressure it would have less power loss than a belt-driven supercharger.

Also, you mention turning up the boost 2.6 PSI. Now, with a boost gauge, would my overall boost show up as 2.6 psi + if I added that much boost? (11.6 psi total)

Or would boost overall be calculated at the lower PSI due to the 12.1 PSIa absolute air pressure here? (meaning, would the boost show as 11.6 psi at sea level, and 9psi up in colorado? or would the gauge still show 11.6 PSI in colorado)?

mastrdrver

You wont make 500hp with the same setup just bcuz their is less air up their. Just like Topfuel and Funny cars run more boost at the Mile High track in Denver, but they still run .3-.5 slower even with more boost and the motors are blowing up more often. All a SC does is compress air, well when there is less air to compress it is going to lose power power.

All your boost pressure gauge is messuring is the resistance in the intake side of the motor, therefor less restriction means less pressure showing on the gauge. So the boost gauge should be the same where ever you go. The SC motors in NHRA Nats add about 10psi when they go up to Denver, they also have more problems with motors blowing up.

a73camaro

Correct on the turbo, as long as you're on the "high" part of the compressor efficiency map.

Yes to the extra boost, the gauge would show as 11.6 PSI. And since boost pressure is measured with a gauge, it would show up as 11.6 PSI.

Now if you looked at absolute pressure for mile high...

12.1 + 11.6 = 23.7 PSIa

and sea level

14.7 + 9.0 = 23.7 PSIa.

If both engines (one at sea level, one in Denver) have the same manifold pressure (absolute) with equal tune, they should make the same power/torque as long as the power adder is not extracting some of that power.

Another reason why TF/FC are slower at 5800' is that there is less downforce on the car due to the thinner air. They make more than enough power, it is getting the power to the ground is what the limiting factor is. Not sure about the percentages of engines blowing up but I'm pretty sure that more than a few blower belts get shredded up here.

mastrdrver

True about the downforce, I forgot about that. Though to calculate how much air is being compressed wouldnt you want to use the compression ratio of the sc into that equation?

B4Ctom1

There is even one other thing to consider beyond densities and pressures. That is the actual O2 content of the air in denver is lower. so your 9 # compressed will contain a diametrically equivalent lower % O2 as well. Sure the spring is made to sweep and open the waste gate at 9# sea level or 9# at bandemeres 5800 feet. But dont expect the same numbers. Blower guys are really screwed. a 8 or 9 # blower kit is rendered to a sad 6 or 7 # here. The guys least affected are those that bring the atmosphere in a bottle. Since there is almost more O2 in nitrous than some engines can burn, nitrous cars are the least bothered from sea level to altitude. Some really huge motored bottle cars can pic up a tenth or so, but the average joe is less.

Air density during the summer months on hot days reaches a huff and puff 7000+ feet indicated altitude air density.

Its bad enough that on the average cars are 1.0 to 0.9 seconds slower compared to sea level here but add to that the kinds of problems faced at sea level tracks such as hot days or humid days or both and suddenly your 15 second LS1 is stomping the crap out of 16 second modified 5.0 mustangs LOL