Cause of lower target boost at elev?

I have been tuning and logging on a cross continent tour (10k miles)

I started with Mickey d's stage 2 map. I hit my target boost from 3 to 7k at sea level with 93 and e85. Now that I am at 6k' in Colorado, my target boost during logging is about 5psi lower across the board. What is causing this and how can I fix it?

 

Mods as follows

2005obxt

750 cc inj, Perrin elh, catless sti up, invidia catless down, custom built tmic.

 

Mike

Btw my learning view shows 2-5 % correction + and Iam at 1.0 with no knock.

And I forgot the fuel pump upgrade

Think about the difference in baro at sea level vs 6000 feet.

Welcome to Colorado! There are compensations for altitude and it's just the ecu doing it's job. It's normal. Since turbos operate on pressure ratio and you've lost 2-3psi in atmosphere your turbo will boost around 2-3+psi less.

 

For reference, at 5400' my observed boost is 92% of my actual targets... which explains why I have targets in the 26's to hit boost of mid-23's mid-range boost.

lol legend, never realized you were from col.

I realize the diff between sea level and 6000 feet which i found to be around 2.9psi.

 

But my Target boost in my map is set to 18.51 from 2600-4000 then tapering to 12 at 6800.. but target during loggin is 13.8 tapering to 11.3, and my actual is 10 then tapers to 6.

 

to clarify, if the diff between sea and col is 2.9 psi, i should see 15lbs or so target.. but i am not. any how i have attached a log, to see if any of you guys in elev seen the same with a vf40 and similar mods..

 

on a side note, i can see why you wanted a hta68 legend.

log0003.csv

When i was in colo springs training when i installed my boost gauge and it was reading about 7psi *stock* when i drove back to Kentucky after i was done my gauge was reading close to 15 :/ The thing about Colorado is, it just f***** hates you, and me and everyone else

Check your "Target Boost Compensation (Atm. Pressure) table. MickeyD's stage 2 for mine has:

 

8.51	11.22	12.96	13.92	14.31	14.70
-38.3	-21.9	-10.9	-4.7	-2.3	0.0

 

So if you are 2.9 psi lower than sea level, you are at about 11.8 atmospheric pressure which then targets about 20% lower boost. 18.5 - 3.7 = 14.8

 

You also lose another 4% if IAT is above 104*. So I can see that target would be less than 14psi.

 

Not sure how the 05 map looks, but it seems reasonable to me.

It appears the WGDC compensation by atmospheric pressure table needs to be adjusted so that you can hit your atmospheric-corrected target boost. These are nearly impossible to adjust without tuning in the intended enviornment (in your case, 1-mile up) and I've found the stock values don't work that well on some of these tables when targeting more boost and WGDC than stock.

Even in Salt Lake (about 4,500ft) stock cars are only hitting about 11psi manifold relative pressure, which is also about 2 psi short of what it's suppose to peak at.

When I was at 6200 ft ASL (Castle Rock) I took boost control away from the ECU with a Hallman.

Even in Salt Lake (about 4,500ft) stock cars are only hitting about 11psi manifold relative pressure, which is also about 2 psi short of what it's suppose to peak at.

 

That sounds a smidge low. What does your ECU show as atmospheric pressure there? I'm guessing around 12.5psi?

 

Stock peak boost pressure at sea level calls for 13.54psi. The ECU uses the following compensation for atmospheric pressure change to alter requested boost:

 

Atmospheric pressure * .05208 + .25

 

This is then used as a multiplier applied to the target boost to reduce it according to atmospheric pressure.

 

12.5 psi atmospheric pressure * .05208 = .651 + .25 = .901

 

13.54 psi target boost * .916624 = 12.19 psi compensated target boost.

 

11 psi is about 1 psi off from target boost after compensation, assuming my atmospheric pressure for 4,500' is roughly correct.

 

Notice that the WGDC compensation by atmospheric pressure table is not tuned from the factory on the 05/06 LGT.

 

 

On another note, there are so many reasons NOT to use manual boost control devices on these cars in this day and age. It's amazing people continue to do it.

That sounds a smidge low. What does your ECU show as atmospheric pressure there? I'm guessing around 12.5psi?

 

Stock peak boost pressure at sea level calls for 13.54psi. The ECU uses the following compensation for atmospheric pressure change to alter requested boost:

 

Atmospheric pressure * .05208 + .25

 

This is then used as a multiplier applied to the target boost to reduce it according to atmospheric pressure.

 

12.5 psi atmospheric pressure * .05208 = .651 + .25 = .901

 

13.54 psi target boost * .916624 = 12.19 psi compensated target boost.

 

11 psi is about 1 psi off from target boost after compensation, assuming my atmospheric pressure for 4,500' is roughly correct.

 

Notice that the WGDC compensation by atmospheric pressure table is not tuned from the factory on the 05/06 LGT.

 

 

On another note, there are so many reasons NOT to use manual boost control devices on these cars in this day and age. It's amazing people continue to do it.

 

Great post. I bolded the last statement.. couldn't agree more, especially if one lives in an area where there is a lot of variety in altitude.

Just noticed I dropped the incorrect multiplier into the last equation. Should read: 13.54 psi target boost * .901 = 12.19 psi compensated target boost.

It should hit those numbers, but logs don't lie. During a 3rd gear WOT log, from a stock 06 LGT 5mt the car peaked at a whopping 11.03 manifold relative pressure. I'm not saying it should be that low, but formulas do not always match real world numbers. I'm sure it didn't help that it was also pulling timing, but heatsoak hot weather and crappy gas just kind of sucks. This car was all stock, it was the base run to compare to the tune.

+1 about the manual boost controllers. It might not be as bad at sealevel, but our little turbo has a hard time on 91 octane and high altitude

Thanks for the replies. ThAts the answers I was looking for. Calgary I believe we are at around 3300ft. I have to do some investigation into my cyl2 miss at idle and the oil being barfed out the vf40 comp side. A hta68 is in the works..