Altitude vs Boost
03-04-2011, 03:19 AM
#1
MBWorld Fanatic!
Thread Starter
Altitude vs Boost
Few days ago went on a nice drive through a mountain range. With the compass app on my G2 can view altitude, so I decided to run a few boost tests. At 7000ft 40F max boost 16 PSI. At 8000ft 40F max boost 15 PSI. There's a noticeable loss of power. My areas altitude in the valley is 5000+ft, and I see max boost around 18-19PSI when it's cold out 20-30F. This seems to suggest a lot of the information I've read regarding altitude and forced induction is not true. I usually find claims stating max boost is still achieved at high altitude. It would appear roughly 1PSI is lost per 1000ft altitude gained? 
03-05-2011, 08:16 AM
#5
Super Moderator Alumni
Having experience with forced induction aircraft, I would not state that forced induction offers maximum boost at all altitudes but, I do know that it offers far superior performance over naturally aspirated engines.
The example I can think of was this: we had flown into Big Bear Lake, CA for a quick stop over on a hot summer afternoon. At an altitude over 7000 feet, the airport is nearly impossible for a N/A aircraft to get off the ground on a hot day. Most of the planes were grounded and the airport traffic was nearly nil. Our turbo engine offered plenty of power (air density) to get off the ground with a full payload. Was it a snappy as the performance at sea level? No. But it kept us going at altitude.
Same with our Supercharged cars, it won't be as snappy as at sea level, but it sure beats the alternative.
The example I can think of was this: we had flown into Big Bear Lake, CA for a quick stop over on a hot summer afternoon. At an altitude over 7000 feet, the airport is nearly impossible for a N/A aircraft to get off the ground on a hot day. Most of the planes were grounded and the airport traffic was nearly nil. Our turbo engine offered plenty of power (air density) to get off the ground with a full payload. Was it a snappy as the performance at sea level? No. But it kept us going at altitude.
Same with our Supercharged cars, it won't be as snappy as at sea level, but it sure beats the alternative.
03-05-2011, 04:03 PM
#6
MBWorld Fanatic!
Thread Starter
I thought you could go to 22psi with a 185mm setup??
Same with our Supercharged cars, it won't be as snappy as at sea level, but it sure beats the alternative.
03-05-2011, 09:43 PM
#7
Super Moderator
^ Spot on analogy from ScottW911.
Used to ride or drive up the San Gabriel Mountains most every Sunday morning. They’re well over a mile in elevation toward the summit. Not unexpectedly, my GF insisted I give up the GSXRs when we got hitched. Be that as it may, ever tried to strike an acceptable mixture strength compromise with Weber, Holley, Rochester or Mikuni carburetors?
Be thankful we’ve a tuned Bosch 2.8 ECU controlling the works.
Seeing how AMG extracted an additional 134 horsepower from the base 3.2-liter M112 with fourteen PSI of artificial aspiration, that same ~ten horsepower per pound of boost yardstick probably still holds true. Setting aside the inevitable adiabatic law of diminishing efficiencies for the sake of this post, that’s been my experience based upon ‘strip trap speeds.
Take comfort in knowing diminished density altitude also affects the gent you’re running alongside.
Be thankful we’ve a tuned Bosch 2.8 ECU controlling the works.
Seeing how AMG extracted an additional 134 horsepower from the base 3.2-liter M112 with fourteen PSI of artificial aspiration, that same ~ten horsepower per pound of boost yardstick probably still holds true. Setting aside the inevitable adiabatic law of diminishing efficiencies for the sake of this post, that’s been my experience based upon ‘strip trap speeds.
Take comfort in knowing diminished density altitude also affects the gent you’re running alongside.
