Mortis101
forum member
I just bought a 2008 GT500 from a guy in east Texas and I was wondering if I needed to have the tune changed to account for the elevation change and 91 octane fuel. (I live in Utah) It has a VMP TVS and a 93 octane tune.
Elevation change question
- Thread starter Mortis101
- Start date
BAKnBLK2010
Harley Davidson FLHTCI
Elevation doesn't require a retune but the octane change could. I think you will be fine without a retune as long as you always run the 91 octane fuel.
For the octane 100% get an update from VMP
Flapjack
Lunatic engine swapper
The elevation does affect the tune. Absolutely. You typically don't need to "fix" it, but the car will run rich until it racks up some long term fuel trims. If you plan on staying at a high altitude long, you should have a tuner adjust timing and your mass air transfer function to compensate. You can get back some of the power lost in high altitude by adding some timing.
The lower octane is not just gas stations being cheap... it's done as a way to lean the car out due to the less dense air. You may be running a lower octane gas, but you also have less oxygen.
Overall, you should be ok with the 93 octane tune and the 91 octane gas... but I would still datalog knock and spark retard to compare with your car at the lower altitude.
My R1 is incredibly sensitive to low octane gas, but still runs fine on 91 in Colorado Springs (+6000ft).
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The lower octane is not just gas stations being cheap... it's done as a way to lean the car out due to the less dense air. You may be running a lower octane gas, but you also have less oxygen.
Overall, you should be ok with the 93 octane tune and the 91 octane gas... but I would still datalog knock and spark retard to compare with your car at the lower altitude.
My R1 is incredibly sensitive to low octane gas, but still runs fine on 91 in Colorado Springs (+6000ft).
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Mortis101
forum member
Thanks for the info guys. I'll email Justin to see about getting an updated tune.
06Mach
forum member
I talked at length with the local muscle local shop HPS.
My concern was 87 tune, with 86 gas.
He told me the reason our gas sucks is elevation.
IE due to elevation 86 is the same as 87
which is why we get 91 instead of 93.
So I'm running 87 on my street and 91 for race.
I was really nervous because I know you can run higher, but should never run lower, but he assured me that his customers run 86 on their regular 87 tunes and all is well.
Then when they hit different states, they just load up with 87 and vice versa.
Hope this helps.
My concern was 87 tune, with 86 gas.
He told me the reason our gas sucks is elevation.
IE due to elevation 86 is the same as 87
which is why we get 91 instead of 93.
So I'm running 87 on my street and 91 for race.
I was really nervous because I know you can run higher, but should never run lower, but he assured me that his customers run 86 on their regular 87 tunes and all is well.
Then when they hit different states, they just load up with 87 and vice versa.
Hope this helps.
Mortis101
forum member
I emailed Justin at VMP and he said all I needed to do was lower the timing 1 degree.
Anyone know where I can find how to do that?
Anyone know where I can find how to do that?
BAKnBLK2010
Harley Davidson FLHTCI
Go to the custome tune section on your handheld SCT device and pull up the current tune you have on the car. Scroll thru the options and see if any of them allow you to adjust the timing. If it is allowed just reduce the timing by 1 degree then download the tune to the car. Some of the guys that write tunes allow you to make this change and others do not.
in your SCT parameters you can adjust global spark
BAKnBLK2010
Harley Davidson FLHTCI
Maybe, maybe not on a custome tune. Not all tuners leave this option open for adjustment.
Yes I know. But since Justin said to adjust it and didn't send a new tune, it's fair to say its open.
BAKnBLK2010
Harley Davidson FLHTCI
I guess I should have read his sig and put two and two together. Sometimes I miss the little things.
Mortis101
forum member
I forgot to post an update.
I was able to adjust the global spark down 1 degree. It seems to have fixed a separate issue I was having with the car hesitating when I started it. Also before I made the change it smelled like the car was running really rich, but I think that has been fixed too.
I still plan on taking the car to a local dyno to get check the A/F ratio and see what numbers it is producing. I appreciate everyone's help.
I was able to adjust the global spark down 1 degree. It seems to have fixed a separate issue I was having with the car hesitating when I started it. Also before I made the change it smelled like the car was running really rich, but I think that has been fixed too.
I still plan on taking the car to a local dyno to get check the A/F ratio and see what numbers it is producing. I appreciate everyone's help.
19COBRA93
Ford Racing
Did you notice an obvious drop in HP going from Texas up here to Utah?
Mortis101
forum member
I had it shipped here so I wouldn't know the difference.
The GT500 has A LOT more horse power than my Stage 3 Roush did though.
I've driven back and forth from CO to lots of places at lower elevation, and yes there is a difference. I never spend enough time at WOT to really notice, but I can see on the Vac / Boost gauge a serious difference at lower power levels. Hills at home that take zero vacuum / low boost to climb can be done at 10" vacuum in lower elevations.
I still would never move!
I still would never move!
Flapjack
Lunatic engine swapper
19COBRA93
Ford Racing
Turbos seem to work best here in Utah as well.
Proto
Junior Member
Back off 2* of timing on your SCT. Done
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Sent from my iPhone using Tapatalk
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