I've got a question bout elevation

[djuosnteisn]

JK, the titties were just to get you to look at this thread.


Here's my question. Since my 3071 MAF g/s (up here in NM @ 5500ft) is nearly the same as Bova's k04 MAF g/s at his altitude, does that mean we're making the same power???

Basically, am i safer to run 21 psi on a 3071 up here? My logic says YES, but i need some confirmation.

I know it's more than shown in our 1/4 mile times. So depressing on how excited i got by breaking into the 13's with a stock turbo (13.98). It just sounds stupid, hahaha.

It's also shown in our uncorrected dynos and shit. Psi for psi we make significantly less power up here.


And lastly, this is a bit off topic, but it seems like our motors are pretty robust under WOT conditions. Only 2 people i can think of that blew during WOT blew cause they're WG lines popped off. Most blow at light loads. And i know the saying "well that's just when it decided to let go..." but i don't believe it. I drive my car fucking hard (read hard, not stupid), so if it's gonna "let go" pulling away from a stop light, it should have let go seconds earlier while i was flooring the thing.

Thoughts?

[Funky]

Our boost gauges display the differential pressure from our manifolds, or in other words, they compare the manifold pressure with the ambient pressure. From my knowledge, stock setup, or any automobile setup that I've seen, also regulates the wastegate using this differential reading. What that simply means, is that the turbo takes the ambient pressure, and slaps 15 LBs (or whatever the boost pressure is set to) to it, and feeds it to the engine.
Ambient pressure drop at 1"Hg every 1000ft, but our engine does not compensate for that amount - I have to live with this BS everyday since I too live at 5300ft.

In the airplane world, we have a gauge in many airplanes, especially in all turbocharged engines, called the Manifold Pressure gauge.



This gauge indicates the absolute pressure in the manifold; so when the engine is off, the ambient pressure is displayed. This gauge works similar to the boost gauges we are all familiar with, but there is no "vac" like in the boost gauges.

What I'm trying to get to, is that in NA airplanes, we set our power (to achieve expected performance) using this gauge, and in FI airplanes, we maintain max rated power all the way up, using the absolute manifold pressure. A constant power output is achieved by maintaining a specific manifold pressure as we climb (adding boost during the ascend, and removing boost on descend).

So, the moral of the story is that
1. PSI is not a very good measurement for calculated performance to begin with
2. Automobile differential boost gauges are simply useless when you rely on them for expected performance throughout different elevations (the only thing they are good for is letting you know if your turbo's hitting its design limit)
3. The only way you can maintain same power is by referencing the your absolute manifold pressure, and using an adiabatic system, which will maintain the same manifold pressure throughout all elevation. The only variable with this setup becomes temperature, and humidity, and the only thing you will have to worry about is your turbo hitting its designed RPM limitation. Otherwise, your engine will feel the same thing, and put out roughly the same amount of power regardless of the altitude, and no, this will not stress your engine.

Trying to calculate expected performance using PSI, or comparing 21PSI to the sea level PSI wont get you anywhere. Since you asked, given that psi = in. of Hg x (0.49118), the difference between sea level and 5500ft is only 2.7PSI, which means that you should only have to add 2.7 PSI to the sea level boost to maintain sea level power. But then again, many things play a role when you look at numbers and compare them using 'normal' formulas that do not take into account any of the fluid dynamic laws that may be affecting the air inside your engine. Things just get too complicated.

So, to compare power, the most accurate answer you can get is comparing your absolute manifold pressure by Bova's manifold pressure, or your own mani pres. from sea level. I guess MAF reading would be the next closest thing, but I don't know how MAF exactly achieves its reading.

Funky

[Scatt Nasty]

so this would explain why I could hit 19 PSI at 5000FT and then drive to 1000FT and hit 22.X

[djuosnteisn]

Thanks funky, pretty damn informative.

And scatt, good question. Here's my thoughts, but it may be way off target.

I'm running the same map now as i was before the 3071. My boost used to hit 19 ~ 19.5 with my k04, and usually taper down to like 17-18. I would log my WG duty cycle, and usually still have fairly high %'s (like 70 or so), which tells me the ecu was still trying for a higher load target.

Now with my 3071 installed, i hit 21 and it just stays there, rock solid till redline. WGDC gets down to like 10-20% at redline, which means i'm right at the target load, but pretty close to going over. 0%'s are bad news, cause that means your boost creeping, and ecu has no control.

So my theory is that the load targets are the same, except my k04 was never able to reach it before it would run out of steam @ 5500ft. And it also means i was running the piss out of the k04 trying to reach it each time i went wot. Now with the 3071, it can reach those loads no problem, so it does. And if bova has similar target loads as i do, that would explain why our MAF g/s are similar.

Seems to make sense to me.