mile high question
evolute,
Check this thread out. It has a post from Shiv about altitude!
-- and my dyno from last week
https://www.evolutionm.net/forums/sh...d.php?t=117735
Check this thread out. It has a post from Shiv about altitude!
-- and my dyno from last week
https://www.evolutionm.net/forums/sh...d.php?t=117735
thanks, but i've already spoken with chronohunter about higher boost levels at higher altitudes.
i'm mostly wondering about octane and how it works with the xede at higher altitudes.
i'm mostly wondering about octane and how it works with the xede at higher altitudes.
I guess what I got out of Shiv's answer was that because the Evo does not control boost by a MAP sensor, then the turbo is not compensating for pressure loss due to altitude. This would mean that the octane rating, if improved by altitude, would also be improved for our cars -- and hence we should be allowed to run the 93 maps.
Then again, I would love an answer from someone who truly knows and is not speculating, like myself
Then again, I would love an answer from someone who truly knows and is not speculating, like myself
Originally Posted by JTB
I guess what I got out of Shiv's answer was that because the Evo does not control boost by a MAP sensor, then the turbo is not compensating for pressure loss due to altitude. This would mean that the octane rating, if improved by altitude, would also be improved for our cars -- and hence we should be allowed to run the 93 maps.
Then again, I would love an answer from someone who truly knows and is not speculating, like myself
Then again, I would love an answer from someone who truly knows and is not speculating, like myself
...It will try and hit your boost number as you climb so the turbo does spin harder the higher you go, naturally compensating for the air getting thinner. It doesn't go for a higher boost number as you climb though (which I think is what you/we want!). It depends what turbo you have and what rpm we're talking about though because the stock turbo doesn't have the capacity to provide 25psi at 11k ft. at above 5k rpms. We just plain run out of turbo. That is why, even at 5800ft on the Mac dyno, the SAE correction applies (340hp on my car, about the same as a sea level stage 1+ on a dynojet). Our horsepower peak is a full 1000rpms lower because we run out of turbo capacity. It interestingly does not affect our torque peak numbers much because that occurs before the turbo runs out of air (so SAE overcorrects the torque figure, 360lb ft in my car).
Because the power curve is so different here any of the sea level maps will not be optimal, the timing, fuel and boost curves are all different. We can be more aggressive in some places and less so in others (= custom map!). So the 93oct sea level map would not be optimal
Disclaimer: These are obviously just my observations from my car on the dyno and on the road so they may not be 100% accurate in all cases, but it sure feels right!
IMO, the SAE correction factor on Mac's dyno is ... umm... somewhat optimistic. FWIW, on the MAC Autosport dyno my stage 1 tuned on 91 Octane pulled an alleged 317WHP using SAE correction (248 uncorrected). When I retuned for 93 Octane with a Stage 1+ (272 cams) in Chicago (also an AWD DynoJet), the car made 292 WHP using SAE correction (285 uncorrected). Needless to say, when I look at those numbers, I have a hard time understanding how the SAE numbers from Colorado are anywhere near being correct. When I look at the uncorrected numbers, they make much more sense. However, having said that, it really doesn't matter all that much, since you shouldn't be comparing numbers from different dynos to begin with (although I'm as guilty of that as anyone else, hehe).
l8r)
l8r)
Originally Posted by chronohunter
just speculating again ...
It will try and hit your boost number as you climb so the turbo does spin harder the higher you go, naturally compensating for the air getting thinner. It doesn't go for a higher boost number as you climb though (which I think is what you/we want!). It depends what turbo you have and what rpm we're talking about though because the stock turbo doesn't have the capacity to provide 25psi at 11k ft. at above 5k rpms. We just plain run out of turbo. That is why, even at 5800ft on the Mac dyno, the SAE correction applies (340hp on my car, about the same as a sea level stage 1+ on a dynojet). Our horsepower peak is a full 1000rpms lower because we run out of turbo capacity. It interestingly does not affect our torque peak numbers much because that occurs before the turbo runs out of air (so SAE overcorrects the torque figure, 360lb ft in my car).
Because the power curve is so different here any of the sea level maps will not be optimal, the timing, fuel and boost curves are all different. We can be more aggressive in some places and less so in others (= custom map!). So the 93oct sea level map would not be optimal
Disclaimer: These are obviously just my observations from my car on the dyno and on the road so they may not be 100% accurate in all cases, but it sure feels right!
...It will try and hit your boost number as you climb so the turbo does spin harder the higher you go, naturally compensating for the air getting thinner. It doesn't go for a higher boost number as you climb though (which I think is what you/we want!). It depends what turbo you have and what rpm we're talking about though because the stock turbo doesn't have the capacity to provide 25psi at 11k ft. at above 5k rpms. We just plain run out of turbo. That is why, even at 5800ft on the Mac dyno, the SAE correction applies (340hp on my car, about the same as a sea level stage 1+ on a dynojet). Our horsepower peak is a full 1000rpms lower because we run out of turbo capacity. It interestingly does not affect our torque peak numbers much because that occurs before the turbo runs out of air (so SAE overcorrects the torque figure, 360lb ft in my car).
Because the power curve is so different here any of the sea level maps will not be optimal, the timing, fuel and boost curves are all different. We can be more aggressive in some places and less so in others (= custom map!). So the 93oct sea level map would not be optimal
Disclaimer: These are obviously just my observations from my car on the dyno and on the road so they may not be 100% accurate in all cases, but it sure feels right!
obviously, we wouldn't want ANY kind of sea level map. so do these altitude adjusted custom maps account for the octane difference (91 acting like 93 in our cars)?
maybe the gas doesn't change when you bring it up here (that's kind of what i've been thinking)? it's just that gas reacts differently with differing amounts of oxygen?
what makes the octane levels important? is it the amount of oxygen in the engine? if so...
less oxygen = less octane needed to run the car properly.
so, if you push more boost to run the same amount of oxygen as you would be at sea level, then you need the same amount of octane that you would need at sea level?
maybe someone here has already presented this answer and i'm just thick....
i have NO IDEA - someone who knows all about how engines work PLEASE CHIME IN before i pull all my hair out!
what makes the octane levels important? is it the amount of oxygen in the engine? if so...
less oxygen = less octane needed to run the car properly.
so, if you push more boost to run the same amount of oxygen as you would be at sea level, then you need the same amount of octane that you would need at sea level?
maybe someone here has already presented this answer and i'm just thick....
i have NO IDEA - someone who knows all about how engines work PLEASE CHIME IN before i pull all my hair out!
Last edited by evolute; Jan 18, 2005 at 11:05 AM.
Lucino,
in a lot of parts of the world gasoline octane is rated in RON. Here in the US it is rated as RON+MON/2, which gives it a lower number. Google it sometime, you'll see what I mean...
l8r)
in a lot of parts of the world gasoline octane is rated in RON. Here in the US it is rated as RON+MON/2, which gives it a lower number. Google it sometime, you'll see what I mean...
l8r)