J337_UNIT

Just some hypothetical thinking here...my question is about whether or not superchargers in particular are affected by altitudes more so than turbochargers. For instance, we all know that N/A engines are adversely affected as altitude increases. So forced induction like a turbo, with a boost set at X psi will remain at X psi until a critical altitude is reached. But for superchargers its geared to the engine, so the gearing I would think has different limitations. Lets say it is geared for 10 psi and its at sea level... As altitude increases, does the psi decrease since its still always at a particular gearing that is connected to the engine? Im sure someone with experience could verify this answer.. such as someone with a supercharger who lives in Colorado or somewhere with high elevation. Basically if what I am saying is true, that engine with a supercharger who boosts 10 psi lets say in Denver Colorado, would boost more at sea level.

blinx9900

well im not an engineer nor do i have excessive experience on SC but my opinion is the gauge may read the same boost level but there is less oxygen per volume of air in higher altitude so you may make less power in high altitude with the same boost level, not sure if that answers your question or if im right, its just my .02 with my basic understanding of science.

wakedoe

Probably true, because a turbo will keep pumping at its maximum while the pressure is lower than w/e the wastgate is set at. A supercharger doesn't have that and is physically connected.

typrdb8

you are correct if you have X PSI @sea level and go up in altitude (with a belt driven device) the boost will go down so for example if you are 10 psi in denver and you came down in elevation your boost will rise and you would need to change your pulley accordingly to stay at 10 psi. Hope this helps

spets

boost will go down, but not too much.

according to a SC calculator on here by Veris, going from sea level to 5,500 ft would lower your psi from 5.9 to 5.1.

HiProfile

Well its based on the RPM and inlet pressure as mentioned, meaning PSi will be less, but the overall power increase will be fairly proportional to the atmospshere pressure at your alt vs sea level.

What really screws things up is how the lower pressure on the exhaust affects things. Turbos benifit a lot since its less backpressure, and a SC should at least benifit somewhat from better exhaust scavenging. In other words, it will make less boost, but make a little more power per PSI.

COMplex.

Sorry for the late reply...

Altitude does in fact have an effect on horsepower in supercharged cars. (Just as it does with NA)

Currently here in Denver with a 3.6" pulley I max out @ 4psi at or near redline.

I drove to Chicago last year, and my car felt much faster the closer I got to sea level. In Chicago I was maxing out at 5psi at or near redline.

When I had my car dyno'd here in Denver, I made 251 corrected wheel horsepower. Meaning, if I went to sea level, I should make the same power on a dyno with no correction factors.

If I take the correction factor off of the dyno chart, I lost roughly 50whp.

I make about as much power as a stock 06 Si would at sea level.

The good news for me is that just about all cars are affected by the altitude, so it's relative. A stock 06 civic si has no chance in keeping up with me at this altitide, since they make 50whp less than they would at sea level.

Hope that helps.

uncledan

Resurrecting an old thread. I am interested in this topic. I tried searching for the calculator that veris has/had posted and can't find it.

Can anyone help with the calculator?

Thanks

Veris

A postive displacement supercharger (ie eaton) is a atmospheric multiplier. So a lower pressure atmosphere (high altitude) results in less boost.

A turbo with a waste gate is an adder. It adds 5psi (spring) at altitude or not so they are less affected by altitude.