[Nimair.ZL1]

Hello folks,

Question about boost at elevation. Right now I'm in Wyoming and about 6300ft of elevation. The DA is anywhere from 8000-10000ft at times. I have a stock upper (2.50) and a lower 9.60" pulley. Also have a cam with 3.5* over lap and 2" headers. At sea level the car was seeing about 11-12 PSI. On my logs here I'm seeing about 5-6 PSI. I don't have any vacuum leaks. Could elevation and DA play that big of a role in how much boost I'm making?

[Camaro1973]

Originally Posted by Nimair.ZL1

Hello folks,

Question about boost at elevation. Right now I'm in Wyoming and about 6300ft of elevation. The DA is anywhere from 8000-10000ft at times. I have a stock upper (2.50) and a lower 9.60" pulley. Also have a cam with 3.5* over lap and 2" headers. At sea level the car was seeing about 11-12 PSI. On my logs here I'm seeing about 5-6 PSI. I don't have any vacuum leaks. Could elevation and DA play that big of a role in how much boost I'm making?

Yep, just take your barometric pressure and subtract that from intake manifold absolute pressure and that is your actual boost psi.

And yes elevation kills boost as well as heat.

Move back to sea level

[JSH]

Originally Posted by Nimair.ZL1

Hello folks,

Question about boost at elevation. Right now I'm in Wyoming and about 6300ft of elevation. The DA is anywhere from 8000-10000ft at times. I have a stock upper (2.50) and a lower 9.60" pulley. Also have a cam with 3.5* over lap and 2" headers. At sea level the car was seeing about 11-12 PSI. On my logs here I'm seeing about 5-6 PSI. I don't have any vacuum leaks. Could elevation and DA play that big of a role in how much boost I'm making?

Do you use HPT? What is your barometric pressure and highest manifold absolute pressure? The difference is your boost.

At 6300 ft., on a nice day you'll see about 11.7 psia barometric pressure (SAE) in your HPT PID data versus 14.7 at 0 ft. And your blower will make about half as much boost at 6300 because it is less efficient. However, you can change to a smaller blower pulley to regain some of the lost boost. I'm not certain as to how much smaller.

At altitude, you need to spin the blower faster and run more spark advance and octane. You'll see the NHRA guys do it this week at Bandimere.

My peak hp was at 6183 on the dyno, so I dropped my shift points from 6900 to 6500. I use a small upper (2.75) to increase hp and torque down low and to reach 6500 quicker (but with worse traction), resulting in lower engine and blower rpm. I'm thinking of trying a 2.625.

[FarmerFran]

Someone needs to invent a variable pulley

[Nimair.ZL1]

Barometric pressure is about 11.9. I just didn’t know that I would lose half my boost lol

[CW3SF]

The altitude and lower boost makes a huge difference. I made 580ish uncorrected in Denver on e70, moved to the east coast at sea level, retuned car and made 740 uncorrected on e50.

[Nimair.ZL1]

If you don't mind me asking, what was your dragy time when you were in Denver and when you moved to the east coast?

[CW3SF]

Originally Posted by Nimair.ZL1

If you don't mind me asking, what was your dragy time when you were in Denver and when you moved to the east coast?

I don’t have Dragy. The car is completely different animal than it was in Denver. Night and day difference.

[Nimair.ZL1]

Would you be able to tell me how much boost you were pushing in Denver as opposed to the east coast?

[CW3SF]

Originally Posted by Nimair.ZL1

Would you be able to tell me how much boost you were pushing in Denver as opposed to the east coast?

I just went back and looked at my threads that I posted at the time to get you the most accurate numbers. And in Denver was 616whp/578wtrq on e84 and making 10 lbs of boost. At sea level now is making 13 lbs boost and 740whp on e50. Both were done on stock pulleys.

Here’s a thread on it.
https://www.camaro6.com/forums/showthread.php?t=611140

[Nimair.ZL1]

Originally Posted by CW3SF

I just went back and looked at my threads that I posted at the time to get you the most accurate numbers. And in Denver was 616whp/578wtrq on e84 and making 10 lbs of boost. At sea level now is making 13 lbs boost and 740whp on e50. Both were done on stock pulleys.

Here’s a thread on it.
https://www.camaro6.com/forums/showthread.php?t=611140

So you lost about 3lb of boost. What bugs me is that when my car was built it was pushing about 12.5lb of boost at sea level ad now it's at 5-6lb. That means I lost 6-7psi of boost. I think I should be losing less

[CW3SF]

Originally Posted by Nimair.ZL1

So you lost about 3lb of boost. What bugs me is that when my car was built it was pushing about 12.5lb of boost at sea level ad now it's at 5-6lb. That means I lost 6-7psi of boost. I think I should be losing less

Yeah it sounds like you have something going on there. The first things I would check are to make sure you have all the air out of the coolant loop and then make sure you have the supercharger bypass valve adjusted correctly, as it could be causing it to bleed off boost if adjusted incorrectly. A search on here should quickly find the instructions.

[Camaro1973]

Originally Posted by Nimair.ZL1

So you lost about 3lb of boost. What bugs me is that when my car was built it was pushing about 12.5lb of boost at sea level ad now it's at 5-6lb. That means I lost 6-7psi of boost. I think I should be losing less

How are you logging boost?

Post a log.

[JSH]

Originally Posted by CW3SF

I just went back and looked at my threads that I posted at the time to get you the most accurate numbers. And in Denver was 616whp/578wtrq on e84 and making 10 lbs of boost. At sea level now is making 13 lbs boost and 740whp on e50. Both were done on stock pulleys.

Here’s a thread on it.
https://www.camaro6.com/forums/showthread.php?t=611140

So, you were seeing ~22# and 25# of manifold pressure?