2.0L Turbo Better at elevation?

Shinysideup

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I'm new to Jeeps and planning to buy JLU soon. I'm excited to get into more offroading, but it'll also be my daily driver (replacing a beloved WRX wagon) as well. I recently moved to live above 5,000 and most of my planned destinations are even higher.

It seems the effect of elevation on the V6 would bring the effective HP below the 2.0L Turbo. With more torque, better fuel economy and electric assist on stop/start it's obvious choice. Right? Or am I missing something and will regret not getting a big NA engine?

Thanks for any advice. Regards.

-- Ryan





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Grimmjpr

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I would say you are correct. All engines N/A or forced induction will lose power at altitude but the forced induction will generally lose less power. If I ended up with a JL it would most likely be the 2.0 turbo. I live at about 4200 ft and spend time off road in areas much higher than that, I could definitely see the benefit of the forced induction for my uses.
 

alphalife9

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If choosing the auto trans no matter the engine choice, then yes the turbo will fair better at high elevation than the normally aspirated V6 as it is less affected by elevation once the boost comes on. The manual trans appears to have an edge on MPG on the 2 door JL compared to the auto trans. It would be interesting to see MPG differences between a manual trans V6 vs. auto trans 2.0T. The V6 engine with boost (I am sure there will be many options coming soon) is what I'd aim for.

I test drove an automatic JLUR at 7,000+ ft. above sea level and it was dare I say fast. I think power-wise, both engines will be plenty.
 

Grimmjpr

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The auto transmission makes a huge difference, my 2017 Grand Cherokee Trailhawk withe the 3.6 and 8 speed feels much faster and more responsive than my 2012 JKR and 2015 JKUR Hard Rock both with the 3.6 and the 5 speed auto even though the Grand is a bit heavier. I know a lot of it is the trans but the 2nd gen Pentastar in the Grand does seem better then the 1st gen. I'm looking forward to the reviews of the new power trains in the JL, Especially the 2.0 Turbo.
 

alphalife9

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The auto transmission makes a huge difference, my 2017 Grand Cherokee Trailhawk withe the 3.6 and 8 speed feels much faster and more responsive than my 2012 JKR and 2015 JKUR Hard Rock both with the 3.6 and the 5 speed auto even though the Grand is a bit heavier. I know a lot of it is the trans but the 2nd gen Pentastar in the Grand does seem better then the 1st gen. I'm looking forward to the reviews of the new power trains in the JL, Especially the 2.0 Turbo.
I agree. The manual has an even lower first gear than the 8 speed still. I have not tried it but I think it won't disappoint.
 

BillyHW

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Is there anyone who can quantify how much power the 3.6L will lose at altitude compared to the 2.0L?
 

Grimmjpr

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I found this on the interwebs kinda explains some of the losses involved.

Engine horsepower

No matter what type of piston engine you are working with, engine horsepower is always dependent on the amount of fuel and air the engine burns. Keep in mind that it's the density of the mixture, not the volume that determines the power that the engine is capable of generating. Power is not a function of the volume of air, it's a function of the mass, or weight, of the air - the actual number of molecules entering the combustion chamber. This is an important factor to keep in mind when discussing turbocharging. Let's look at an example.

Let's assume a standard day, and we've got a TSIO-550-cubic-inch displacement engine at sea level. At sea level field elevation, that engine will inhale 550 cubic inches of air for every two revolutions of the crank. It would also inhale around 550 cubic inches of air in Denver, at 5,000 feet altitude, on a hot day. But the actual number of air molecules entering the combustion chamber, and of course the resulting power, is going to be very different in these two examples. In Denver, there's fewer air molecules at that altitude to support combustion than there are at sea level. The result is less power for the same volume of air.

The bottom line is this. We can only burn more fuel if we build a larger engine, or we artificially cause a small engine to breathe as if it were larger than it really is. And that's what we do with turbocharging. We cause a small engine to breathe as if it were a larger engine.

Let's go over a few principles of turbocharging. Keep in mind it's not only the cubic-inch displacement of the engine that it's rated at and its rated manifold pressure that determine the engine's performance. Power is also affected by the temperature of the air as it's swept into the cylinders. The temperature of the air greatly affects the density of the air. It's the weight of the air, not the volume, that produces the power.

Now at sea level, assuming a standard day, sea level air density is 0.0765 pounds per cubic foot whereas at 10,000 feet, on a standard day, air density drops to 0.0565 pounds per cubic foot. So in a naturally aspirated engine, let's say it's rated at 100 horsepower at sea level. It generates only 73.9 horsepower at 10,000 feet.

Why turbocharge?

So why do we bother turbocharging? Well, for the simple reason that power diminishes with an increase in altitude. How much manifold pressure is lost for every 1,000 feet of altitude gained? Most of you know the answer to that. It is approximately 1 inch for every 1,000 feet of altitude. And that calculates to around 3 to 4 horsepower lost for every 1,000 feet gained. Remember, power is inversely proportionate to altitude gained. Increased altitude comes with a price - loss of power. At about 18,000 feet, the air pressure and the oxygen molecules are about half that of sea level pressure and air density. The bore stroke of the pistons hasn't changed. We are still drawing in the same volume of air. However, there's less mass, so there's less oxygen to mix with the fuel - there's less to burn. So it shouldn't come as a surprise that a normally aspirated engine is only going to produce about 50 percent of its maximum rated power at 18,000 feet. So we need some method to pump more air into the induction, to increase that air going into the induction at increased altitudes. And turbocharging provides that additional mass of air required to boost an engine's power output at these varying altitudes. AMT

Sea Level: Units of Pressure
Inches of Mercury = (in. Hg.)
Atmospheres = (atm)
Kilopascal = (kpa)
Millibars = (mb)

Pressure equivalents to: 1.0 atm = 29.9 in. Hg. = 760 mm Hg. = 101.3 kPa = 1013.25 mb

Atmospheric Pressure = 14.7 psi & 13 cubic feet of air = 1 pound
Power Loss due to Altitude

Air Density decreases at a rate of 2.9% - 3.0% for each 1000 ft. of elevation above Sea Level. See Standard Atmosphere below for background information.

Naturally Aspirated: Atmospheric Pressure 14.5 psi (It's hard to ride at sea level 14.7 psi)
Atmospheric Pressure @ 9000 feet = 10.5 psi
Pressure Loss = (14.5 - 10.5) = 4.0 (4.0/14.5) = 27.58 % @ 9,000 feet
Does a Turbo lose power with altitude? Yes!

Atmospheric Pressure = 14.5 psi, Boost = 10 psi, Total Pressure = 24.5
Atmospheric Pressure @ 9000 feet = 10.5 psi + Boost of 10 psi = Total 20.5 psi
Approximate Pressure Loss = (24.5 - 20.5) = 4.0 (4.0/24.5) = 16.32 % @ 9,000 feet

The power loss due to altitude is much less with the Turbo. The critical difference is that you can flip the switch on the Turbo to 15 lbs boost and get your sea level HP!!

Turbo considerations: As altitude is increased the turbo fan must increase rpm to maintain a constant boost pressure. With large displacement engines (read 1000cc 4-strokes) the turbo fan may have to spin faster than is efficient. The result is slower acceleration. The cure is a larger turbo or lower elevation.
 

alphalife9

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Is that for a naturally aspirated engine?

Supers and Turbos also lose but not as much...but how much do they lose?
Considering the turbo starts with 15 peak HP less than the V6, I would guess that they are fairly close on power at significant altitude. Torque is a different story.

To have a more accurate yet simplified idea you'd need to know the max PSI the turbo is putting out. I looked but couldn't find it.
At 5,000 ft. above sea level, atmospheric pressure is about 12.3 PSI vs. 14.7 PSI at sea level. The intake system usually takes away about 1 PSI so the manifold sees about 11.3 where you are vs. 13.7 at sea level in the V6.

11.3/13.7 = .8248 * 285 = 235.07 HP

Assuming the turbo is putting out 12 PSI (I don't know, just a guess):
12+11.3 (Intake restriction/ducting still applies) = 23.3 at 5000 ft. at peak boost vs. 12+13.7 = 25.7 at sea level at peak (12 PSI) boost.

23.3/25.7 = .9066* 270 = 244.79 HP

So yea pretty close.

Other things to note: Turbo lag (11.3 PSI at "zero" boost up to 23.3 at 12 PSI of turbo boost)

2 liters won't compare to 3.6 liters until the turbo starts doing its thing.

The mild hybrid system in the 2.0 has a part to play and is unaffected by altitude.
 
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Shinysideup

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Thanks for all the excellent responses. Read them all thoroughly. I've been wondering what the relative affect on boosted vs NA here is. Great information, thanks!
 

Chicago

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I would say you are correct. All engines N/A or forced induction will lose power at altitude but the forced induction will generally lose less power. If I ended up with a JL it would most likely be the 2.0 turbo. I live at about 4200 ft and spend time off road in areas much higher than that, I could definitely see the benefit of the forced induction for my uses.
When will the Turbo be available?
 
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Shinysideup

Shinysideup

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There's a couple of other threads on the forums about this, like this one. I have several calls out to dealers, so expect to hear as soon as orders are possible. The rumors seem to be "soon" (Feb?) and special orders will take priority, and dealer allocation will show up on lots in the summer.

It'd be cool if FCA prioritized turbo orders by customer elevation :)
 

Chicago

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There's a couple of other threads on the forums about this, like this one. I have several calls out to dealers, so expect to hear as soon as orders are possible. The rumors seem to be "soon" (Feb?) and special orders will take priority, and dealer allocation will show up on lots in the summer.

It'd be cool if FCA prioritized turbo orders by customer elevation :)
Thank You
 

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