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Discussion Starter #1
I noticed that above 7,000 feet my truck is not quite as quick taking off from a stop. Once it gets wound up above a few mph it's all there no problem. Anyone notice this or have a fix? I figured it was the reduced air pressure at low tubo speeds which the turbo fixes upon getting a little more rpm.
 

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X,


I live at 6000 ft here in Colorado, and I don't really see any "hesitation". I do notice that when I travel back east and get to lower altitudes that the power roll-on comes a little sooner. I just put that down to air density. At 6000 feet you have about 1/3 of the oxygen that you have at sea level.


Regards,


John
 

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Discussion Starter #3
Thanks CS-Dmax,

I guess it really isn't hesitation, compared to sea level, just a initially a little sluggish off of the line which disappears after about 3-4 mph. It tows just fine up in the mountains.
 

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It's probably cavitation caused by the Cat filter
 

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Seriously, it is just the difference in air density that you are seeing. My other turbo car takes 10 psi of boost to equal the power of an 8 psi car at sea level. There is just more air molecules in the air at sea level. My car measures 84 kpa of atmo pressure at 5000 ft in Colorado and at 10,000 feet, it will not make more than 12 psi due to air density.





Jess
 

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jesshd said:
It's probably cavitation caused by the Cat filter

Hahahahah....veeerrryyyy funny! Thats a good one!
 

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Discussion Starter #7
HA! That was a good one jesshd. I stil haven't had it up in the mountains with the CAT yet. We'll see this winter. Love taking it up on the mountain roads with the T/H switched on, tapping the brake for a downshift.
 

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CS-Dmax said:
At 6000 feet you have about 1/3 of the oxygen that you have at sea level.

Duh...I left out a key word..."less". As in, about 1/3 less oxygen at 6000 feet, than at sea level.


Mods, after you get the spell checker, some of us need you to work on a "oops checker", to stop dumb omissions like this one!



John
 

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Discussion Starter #9
Hey, I believed your original 1/3 of oxygen. Last July went backpacking with about 45# pack, only 5 miles but an elevation gain from 8,500-to-9,500, and it felt like there was only about 1/3 oxygen by the time I got there.
 

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Same reason why a car dyno'd at sea level will make more power than one dyno'd at 5000 ft when you look at un-corrected power readings.





Jess
 

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Discussion Starter #11
Doesn't the turbo compensate for air density differences in our diesel engines?
 

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Mr X said:
Doesn't the turbo compensate for air density differences in our diesel engines?

Yes, but it takes a second or two to do so, hence the hesitation. On turbo charged aircraft the altitude that sea level horsepower can no longer be maintained is refered to as the critical altitude. On the Dmax this altitude should be close to the point where the wastegate no longer opens due to lower air density. I don't have a clue where that altitude is though.
 

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Discussion Starter #13
10/4, thanks all for the explanation. I kind of figured it was like that but hadn't seen any other reports of this.
 

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Discussion Starter #15
Likewise here in CA, 1.25 miles from the beach at sea level. But only 100 miles from 7,000-8,000 foot Big Bear Lake in the mountains and winter snow.
 
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