93

"PowderHound" (PowderHound) 10/02/2013 at 00:09 • Filed to: None

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If there is one thing that seems to suck about Utah so far, it's that there is not a rampant amount of 93 octane. Oh yeah… and the beer is a bit watered down.

HammerheadFistpunch > PowderHound 10/02/2013 at 00:16

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you don't need 93 here, higher elevations. I ran 91 pump just fine for many many years on my turbo subi, not to mention that you get a little higher than rated with manditory e10.

ChemicalCutthroat > PowderHound 10/02/2013 at 00:17

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That is such a smooth gif. Its hypnotic. I hope the beer gets better.

PowderHound > HammerheadFistpunch 10/02/2013 at 00:19

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It seemed like it got similar gas mileage from colorado to here. Nebraska though, it could have been the doing 80 with a kayak and ski box but getting 200 miles to a tank vs 300+ was a bit of a downer. I really need to learn about this higher elevation thing and how it effects everything I do

PowderHound > ChemicalCutthroat 10/02/2013 at 00:21

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Well there is some sort of proportion of me not being used to the elevation and the beer being slightly less alcohol that works for me.

ChemicalCutthroat > PowderHound 10/02/2013 at 00:22

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I can almost believe that.

HammerheadFistpunch > PowderHound 10/02/2013 at 00:27

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its not the octane, its the fact that you are about 30-40% lower air density. so NA you are getting less power and less efficiency, with Turbo you get more lag and less peak boost (depending). assume 7% power loss per 1000 feet NA, and no real loss of peak hp turbo until you get to past your turbines operating range (subaru started to dip off ~9,500 for me but the lag was terrible up there)

HammerheadFistpunch > PowderHound 10/02/2013 at 00:27

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its not the octane, its the fact that you are about 30-40% lower air density. so NA you are getting less power and less efficiency, with Turbo you get more lag and less peak boost (depending). assume 7% power loss per 1000 feet NA, and no real loss of peak hp turbo until you get to past your turbines operating range (subaru started to dip off ~9,500 for me)

PowderHound > HammerheadFistpunch 10/02/2013 at 00:46

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Wait… So I get more lag, less boost and yet still retain my peak hp?

desertdog5051 > PowderHound 10/02/2013 at 01:50

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Here is an interesting fact about altitude and turbos.

"Turbocharged vehicles lose power at altitude for various reasons.

A turbo doesn't care about psi. It only cares about pressure ratio. If you are at sea level (14.7psi ambient) and want to produce 14.7psi boost, the turbo workload is 2.0 pressure ratio. Right now, my altimeter watch is indicating 12.02psi ambient. For the same turbo to produce 14.7psi boost, the turbo workload is 2.22 pressure ratio ((ambient+boost) / (ambient). It is working harder to produce the same PSI.

The problem is that when turbos go higher and higher in the pressure ratio metric, they produce less additional PSI and more heat. Hot air = bad.

To compound the problem, the intercooler is less efficient. At altitude, there are less molecules moving across the intercooler fins. It is therefore less efficient at drawing heat away from the intake charge.

Some cars (Sti, I believe) have ECUs that are tuned to reduce boost at altitude. That reduces the stress on the turbo by making it work at the same pressure ratio.

BMW will up boost to compensate for lower ambients. However, it does not fully compensate. That implies to me that in stock form, the turbo has enough headroom to spin faster and compensate, to an extent, for the thinner air.

Throw in a tune and the turbo is working incredibly hard at altitude".

desertdog5051 > PowderHound 10/02/2013 at 01:58

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Another piece to peruse.

"

How Altitude Affects Aircraft Performance

For those new to the world of flying, a common

misconception is that manufacturer rated aircraft engine power is maintained throughout aircraft operation. In other words, if an aircraft is rated for 300 horsepower, it is not always understood that this does not mean the aircraft engine will continue to perform at 300 horsepower as it climbs.

In reality, because all aircraft engines are dependent on the consistent intake and compression of air for fuel combustion, the amount of power an aircraft engine can produce is directly dependent upon air being pumped into the engine at consistent pressure and density. However, because atmospheric air pressure changes as an aircraft gains altitude, air density is diminished, causing a relative decline in engine horsepower.

A normally aspirated engine in fact typically loses about 3% of horsepower for every 1000 feet of altitude".

Dusty Ventures > PowderHound 10/02/2013 at 02:56

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On the bright side you could run into senor Block at any time

Chteelers > PowderHound 10/02/2013 at 08:09

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Eat, drink, and be happy. Because tomorrow you might find yourself in Utah.

HammerheadFistpunch > PowderHound 10/02/2013 at 11:49

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Basically. Since there is less atmosphere at elevation your turbine is starting from behind the curve. Most factory turbo's can make up the difference in pressure you loose at elevation by simply spinning faster and longer, but there is a point at which you leave your compressor envolope and you generate more heat than boost. For me that happened around 9500 feet (parly's summit) where I would notice I wasn't hitting peak boost anymore (2005 forester xt). its roughly 15psi sea level and 11 psi at 10000 feet so lets say you have 12 psi boost before your wastegate opens, that means 15+12 = 27 psi manifold pressure, so its easy to stay in the boost map low in the curve and at the peak, at elevation you are 11+12 = 23 psi which leaves your turbo on the hook to provide 4 additional psi to meet your wastegate's blow off. The turbo on my subi could do it, but starting at a 4psi deficit at elevation (snowbird parking lot) combined with the low compression ration meant I had to really rev the engine to spin the turbo enough to give be decent torque without stalling. I used to stall at lot at elevation until I got the hang of it. So as long as your turbo can make up the difference in pressure you will keep your peak boost, but because you need your compressor to be spinning faster to do it, you will have less total manifold pressure at sub peak than you would at sea level. It could be worse though, you could have an NA car. My forester had power to spare all over Utah because I never really lost peak boost, but my cruiser....ouch. That thing is doggin it over the pass.

PowderHound > HammerheadFistpunch 10/02/2013 at 12:02

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Well that is just crazy. I will have to watch my boost and see what I am hitting. Is there any reason to be concerned for a blown turbo due to the excessive heat? I know what you mean about NA cars. When I had my old 99 legacy it was a pain in the ass trying to get up over parleys to park city

PowderHound > desertdog5051 10/02/2013 at 12:04

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So with the intercooler being less efficient and the turbo having more heat should I be worried about blowing a turbo easier? Any preventative things or ways to have things work better at altitude?

HammerheadFistpunch > PowderHound 10/02/2013 at 12:05

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I wouldn't worry too much about excessive heat, you aren't at peak boost at 10,000 feet very often for very long.

desertdog5051 > PowderHound 10/02/2013 at 12:10

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I would consult the dealer of your brand. They should know more about it. I'm not an expert. That was a reprint of an article I found on the subject.

PowderHound > desertdog5051 10/02/2013 at 12:21

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Thanks for the info, it's something I really didn't think about before