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Re: Switch to regular 87 octane for high altitude driving Posted by John Williams [Email]  (#1982) [Profile/Gallery]
(more from John Williams) on Sun, 13 Jul 2008 11:17:57
In Reply to: Switch to regular 87 octane for high altitude driving, Notnoel  [Profile/Gallery]
, Sun, 13 Jul 2008 07:19:16
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Jak did all my altitude tuning for my ng900 in Denver and got the car running extremely well and has tuned quite a few cars up here in Denver. I would give Jak a call and let him know you are at altitude and maybe he can tweek a chip for you to run at elevation.
The first step would be to find out what you're a/f is at wot and let him know so he can make adjustments.
What is strange is that everyone says you need less fuel up here, but under wot and open loop, my car actually required more fuel to make the same boost that at sea-level. More timing can be used at elevation as well and the tune that works on my car at elevation would not work well at sea-level. Jak tried one tune that was working great for me up here and it was pig rich at sea-level, but just right for my car in Denver.
My theory on the a/f is that since the turbo has to make up the pressure loss, around 2.5-3psi from sea-level, the turbo has to actually work harder to make 20psi than at sea-level, the turbo up here has to really make 23psi or you need to see 23psi on the gage, which is pressure over atmosphere pressure, around 12.5 psi here in Denver and 14.7 at sea-level and of course on hot 90F days, its more like 11.5...
If you see 20psi on you're gage, you are really running about 17.5psi absolute. To run a true 20psi here in Denver, you would need to see 23psi or so on you're pressure gage. That is going to require more fuel than a set-up tuned for sea-level...
Since everything is working harder, turo, ic is also 15% less efficient, more fuel is needed up here under wot open loop to maintain the power and keep knock at bay.
Good Luck,
John
posted by 75.71.1...
, Sun, 13 Jul 2008 11:20:08, Sun, 13 Jul 2008 07:19:16, Sun, 13 Jul 2008 11:17:57 <-- Viewing This Message
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