RedBaron

Can anyone help shed some light on the ability of the supercharger in the new E55 to maintain horsepower at altitude? Say 5,000 ft. In other words, does a supercharged engine lose horsepower in the same fashion as normally aspirated engine, or does the S/C normailze the boost in the cylinders at all altitudes?

Any info in general, or info specific to the E55 engine is appreciated.

anerbe

Sorry to say, but from my understanding, at higher altitudes, a supercharged engine will perform less than at lower altitudes, becuase the supercharger has less dense of air to force in the engine per revolution.

For the E55 with a supercharger and intercooler, although the temps will be cooler by the intercooler, the air was less dense to start with, and in turn will be more dense after going thru the intercooler, although not as dense as it would be at a lower elevation.

James F. Cannon

Any internal combustion engine will make less power at higher altitudes. Superchargers and turbochargers can compensate to some degree if they have some excess capacity at sea level and are using a bypass valve which can adjust (closing as barometric pressure decreases) as needed. I believe such systems were developed during WWII for fighter aircraft attempting to gain altitude and performance advantages over adversaries. Hope this helps!

Mach430

At higher altitudes, air is less dense, and thus boost is decreased.

James F. Cannon

Mach430, true but if the compressor utilized is of sufficient capacity to produce excess boost at sea level, it can then compensate at higher elevations.

Mach430

True, but since the boost pressure is determined by the rpms of the SC pulley, either the SC pulley or crank pulley would need to be changed to compensate for the loss in atmospheric pressure at higher altitude. If you take a supercharged car that puts out .5 bar (7.25 psi) at sea level, and take it up to 9,000 ft, it will have less power, as the presence of oxygen molucules is less dense at the higher elevation.

jswedberg

I think what James is saying pertains to, say, a turbocharger with a wastegate - if the wastegate is set to an absolute pressure, you'll get that pressure no matter what (as long as the turbo can supply it) regardless of altitude.

Superchargers won't do that unless there is some sort of pop-off valve or wastegate that limits power at sea level. They are mechanically limited because their output is in direct correlation to engine rpm.

James F. Cannon

jswedberg, you understand what I am trying to say. Even superchargers vary in capacity and may put out more air than is needed and utilize some type of bypass or relief valve. Anyway, just trying to say supercharged engine will still produce more power than n/a at higher altitudes.

Pierre32///AMG

I can tell you my own experience here at Colorado 5,450 fts. and my C32 is affected for the altitude. For example my car has H&S chip and BMC filters and I am putting at the Dyno 255 rwhp
Now, after having long conversations with Brandon Kleemann USA (awesome people) he told me that here at this altitude a Kompressor engine losses so far between 15-17% of power, turbo engines 7-8%, and normaly aspirated 20-22%.
Also he told me that the Kompressor losses so far 0.2 bar at 5,450 fts, thus on this circumstances one way to fix that is going for a Evosport or Renntech pulley and for sure you will get a huge improvement. Easy and cheaper to arrange than a normally aspirate car. Turbo engines another story.
Next week I will order one of these and I will post Dyno before and after....and for sure I will get huge imporevent :p , if so a bigger gap than a "sealevel" configuration

RedBaron

Thanks for the info. Pierre32, I'm interested to see what you come up with on the new tests. Sounds like a new pulley might do the trick, but more than likely the car will have plenty of ponies even de-rated at altitude!!