01ITR#700

Alright guys, whats the deal? We always hear about turbo charged cars are less effected by altitude than NA cars right? Ok, why and what margin if any can I guestimate on my sea level times since I'm stuck running at Bandimere Speedway which is at 5800ft. above sea level? For a little reference for everyone on how bad altitude sucks: Stock Type R's run low low 16's here, high high 15's. I got a 15.6 out of my R bone stock, I drive pretty well and drove my car hard to hit that time. Now corrected to sea level my 15.6 run would have been a 14.5-14.6 which is right on pace with most Type R's at sea level.

Now I did a full custom turbo kit, Turbonetics 60-1 HIFI turbo, REV Hard manifold, stock head, stock bottom end, 6.5psi, Stock injectors, Vortech 12:1 FMU, and an Accel inline fuel pump. Basically a ghetto fuel setup. I ran a 13.5 @108 w/ this setup here w/ a slipping clutch, street tires and full interior w/ a 2.3 60 ft. Those traps indicate low 13's at worse assuming the clutch wasn't slipping. So how do I go about correcting that for sea level? I'm willing to say that I think that's a high 12 second pass at sea level, which I assume is pretty good for the setup I have

Thanks for any info, I appreciate it. I'm just trying to get this figured out so I don't have to explain altitude and it's effects every time I talk about my times up here etc...
M

Mr. Softee

its my understanding that becuase boost pressure is read in the manifold, it doesnt matter what altitude you are at, pressure is pressure.

*Boostwerks*

ahahahaha......exactly.

I should be running high 13's down at sea level, but I'm stuck with running high 14's because of our altitude.

I have been lead to believe, that we are able to boost 2-3psi more for a corrected HP. Assuming that the turbo used can safely boost the air that high, everything should be fine.

I would personaly be running 12psi right now on my T-25, but the turbo is just so small I'm afraid it will heat the air to the point of silent detonation.

Just ask Dave Landry (I know you have heard him from HAI)....he is now boosting almost 30psi on his DSM just to get to the 550HP WITH the 75 shot. At sea level he would most likely be well over 600.

b_edson

Yeah, I'm in Colorado as well, so I am wondering the same thing. Everyone I ask has a different opinion on it.

*Boostwerks*

You left out the most important factor in that statement.

AIRFLOW.

Pressure AND airflow, are what determine a cars power output. You can't just look at one, and make a decision on how much power the car should be making.

At 12psi up here in Denver, we are only FLOWING as much air as someone else at only 9-10psi down at sea level.

01ITR#700

I couldn't agree w/ you more on this point. BUT...The particular air you are referring to is indeed more dense down there then up here correct? Therefore, our 9-10psi is producing less power overall correct? I may be completely wrong, but hey, thats why I posted this thread
M

*Boostwerks*

Exactly.

We are ALL making less power up here at the same boost pressure as someone would with the Exact same setup down at sealevel.

To make this into a visual....

The Air particles or O2 (the only air particle that matters), are spaced very far apart up in our high altitude.

Example:

Sealevel: a 1ft sq box is filled with 100 O2 particles because of all the wieght of the atmosphere compressing them into the box.

High altitude: a 1ft sq box only has 70 O2 particles because there is less atmosphere above compressing the particles in the box.

To counter act the drop in pressure of the atmosphere, we are forced to boost more to reach an equivilent power output.



[Modified by Bryson, 12:31 PM 9/30/2002]

The_Head

I had my car dynoed in SLC a while back and the SAE corrected WHP was 140. uncorrected was 115, a loss of 18%.

The_Head

I have also heard that. You lose 2 psi of power at these altitudes (4000 ft+)

But is it the amount of AIR you are flowing different, or is it the amount of OXYGEN?

ijjz

This is a very rough reasoning:
The air is thinner the higher you go up, so the turbo should help out in high altitudes. That case, you should be significantly faster at sea level because the air is thicker and there is more to push.

This is just a crazy rant:
But can weather replace the missing air? A car will be faster in 50 degree chilly weather, as compared to 90 degress hot and humid weather. More then likley the higher you go up, the colder it gets. So can could it theoretically replace the missing factor of thicker air? The lower you get, the warmer it gets, and etc. Colder weather usually allows you to boost a little more as well.

*Boostwerks*

no....

1st of all....Our temps are almost the same as everywhere else, execpt during the winter.

2nd.....Temperature will not make the density of the air change anywhere near the amount of altitude will. Temperature is a factor in the overall density of the air, but it still does not make up for the pressure difference.

I don't know exactly by how much, but I think it would be a huge temp difference to get the air to equal the density of sealevel.

B00STeD

that 13.8@108 sounds about right with a 2.3 60 ft. and sorry tires. it should be the same at sea level!

01ITR#700

13.5 @108...With a good clutch it's 13.2-13.3 easy...
M

DirtyLude

This is all wrong.

12psi is 12psi at sea level and at 6000 feet it's the same flow, the turbo just has to work harder at 6000 feet to pull in that less dense air to make it 12psi. When people talk about psi it's measured in absolute pressure.

In any car with a MAP (manifold ABSOLUTE pressure) sensor, if you have datalogging ability you can turn on the car without turning it over and see what the absolute pressure is. Last time I checked on my car the pressure happened to be 2 KPa which was just more than sea level pressure. Someone at a higher altitude might turn their car on and it'll read -2 KPa, which is lower than sea level pressure. With the same car at WOT running naturally aspirated I get the benefit of 4KPa extra pressure and air density and my car will make more power.

This does not apply to turbos. 12psi is measured in absolute pressure and is the same everywhere, here or in space. Given the air has the same humidity and temperature you will have the same air density. The only problem you will encounter in thinner air is that the turbo works harder and may go out of it's efficiency range, is harder to spool up, and the IC is not as efficient in thinner air.

dbman96

If you're controlling boost with a mechanical wastegate only, you will need to increase boost since it measures boost relative to atmospheric pressure, so if it's set at 9 psi, it's boosting 9 psi OVER atmospheric.

Atmospheric + Boost = Total

Sea level:
14.6 psia + 9 psig = 23.4 psia

Mountaintop:
13 psia + 9 psig = 22 psia


If you've got an electronic boost controller that controls boost based on a MAP sensor, it is reading ABSOLUTE pressure and you will make the same power at altitude as at sea level or in death valley and you should have no performance loss. Your intercooler may become slightly less effective since the density of air cooling the fins will be lower at high altitude and it will be capable of taking less heat out of your intake charge.

DirtyLude

Good point about the wastegate regulated boost pressure. I didn't think of that.

01ITR#700

Good information guys!...But the inevitable question...
If I drove my happy *** out to Cali or some other low altitude track somewhere would my times improve? Ofcourse thats assuming the driving is consistent etc...
M

1.8T_EG

... another point of view... one of my friends got a wrx in the fall of 01... then during spring break 02 we road tripped to texas... and lemme just say this... i dont care what theory says... we could FEEL the extra power!!!... so, from my little experience with boosted cars between colorado and texas (who know what altitude)... there was a great difference... my .02...

Phantom

here's the NHRA altitude correction factors so no more of this 2psi, % hp BS, it's calculated for you for your particular altitude.

http://www.geocities.com/silver_pilate/altitude.html