How much Boost lost due to Altitude?

SheepDog

Member
Established Member
Joined
Mar 2, 2018
Messages
30
Location
Middle Coast
Hello All,

I have recently installed a Procharger on my 17' GT with a P-1x headunit, and a 3.5" Pulley. I live in Colorado and was wondering how much boost loss others at this altitude are seeing? I was under the impression that the 3.5" pulley would be good for somewhere around 12 psi at sea level, but I am only seeing between 6-7 psi at redline. I also have Kooks headers so that should also create about a 1lb loss in measurable boost, but is losing another 4ish PSI reasonable at 5500 feet?
 

Norton

Long-time SVT Enthusiast
Established Member
Joined
Dec 11, 2012
Messages
3,167
Location
Colorado Springs, CO
Formulas involving ABSOLUTE air pressure (e.g., 14.7 PSIa @ sea level, ~12 PSIa in Denver, etc) are required to compute exact numbers. In my experience, however, boost loss due to altitude is about 1lb for every 2K feet of elevation. (e.g., My 2013 GT500 was rated to produce max boost of ~15lbs at sea level. This translated to ~12lbs at ~6K ft of elevation.)

Based on that, I'd expect a loss of just under 3lbs at 5.5K ft elevation.
 

SheepDog

Member
Established Member
Joined
Mar 2, 2018
Messages
30
Location
Middle Coast
Thank you Norton, That is the general consensus across a few other forums I have come across as well. My logs don't indicate a boost leak or belt slip, so I guess I just need to pulley down a bit.
 

luker669

Active Member
Established Member
Joined
Apr 30, 2017
Messages
220
Don’t just look at you altitude check the density altitude. I’m at 3200 feet but in the summer my density altitude is usually over 6000


Sent from my iPhone using svtperformance.com
 

SheepDog

Member
Established Member
Joined
Mar 2, 2018
Messages
30
Location
Middle Coast
Thank you, I didn't factor that in. I've only ever had Turbo cars before, and the Wastegate operation is based on actual pressure so the turbo will simply spin harder to achieve desired boost. (Provided it isn't mechanically limited) I guess since the Centri's are only ever going to be spun as fast as they are driven, a given impeller speed will indeed produce more or less boost based on air density.

Looks like on average 90 degree summer day in my town, the Density Altitude is 8627 feet, so basically the Moon. This would certainly cause the 5 or so PSI loss I'm seeing. Looks like on a nice cold winter Day, I will get all of that back, with a DA of 4762 Feet. This also comes with frozen roads and cold tires, so more power and less traction. Maybe I need 2 Prochargers. ;)
Thanks for the help Sirs.

Here is a link to the calculator I was using. Density Altitude Calculator - English/Metric
 
Last edited:

SheepDog

Member
Established Member
Joined
Mar 2, 2018
Messages
30
Location
Middle Coast
Just thought I would follow up on this. I went down 1 size pulley to a 3.4". at 7200 RPM, I am seeing 8.3 PSI. At sea level this would be somewhere around 13 PSI. With the P-1x, OEM Harmonic balancer, and this 3.4" pulley the blower is spinning at 61,319 RPM at 7500 RPM which is basically the max recommended speed for the blower. I think that if anyone else is considering a Centri and lives at high altitude, I would have to recommend going with a larger head unit like the D-1x or Paxton2200. You won't have to spin it so hard to achieve the kind of boost you want.
 

Users who are viewing this thread



Top