Subaru: Turbo -vs- Naturally Aspirated

[DerJaeger]

I'm in the market for an '05+ Subaru Legacy or Outback wagon and was wondering if anyone here has driven both, the 2.5L turbo and the 3.0L naturally aspirated motors at high altitudes and on mountain roads?

I'll be living at ~4,500 ft and regularly driving mountain roads to 8,000 ft, so the turbo seems to make more sense since power can be more or-less constant**, rather than losing power with altitude. However, in my experience a turbo can be a pain to drive on mountain roads or in heavy traffic, because if the gearing and turbo is not set up for it, it's hard to keep it on boost (when driving up mountain roads with 20 MPH hairpin bends and the like) making the turbo less than helpful in terms of making up for power loss at altitude.

I'd appreciate feedback about what these two Subaru motors like in real-world mountain/high altitude driving conditions.


** I'm assuming that the Subaru turbocharged motors perform dynamic ECU-remapping and wastegate adjustments in response to altitude changes. If they don't, please chime in here and let me know.

[DJSapp]

Test drive the turbo. I have the n/a simply because during the test I was doing 70mph in a 30. It was too much fun and I can't afford those tickets.

My 06 impreza doesn't have any issues driving from sea level to Kirkwood (7900') fully layden with people and gear.

[karpiel]

If it were me, I would get the 3.0, it's a fucking subaru, not exactly a fun car. Not saying the turbo is bad, it's actually quite handy on steep grades, but again, it's a fucking subaru.

You have to make the turbo work for you by left foot braking on low speed twisties.

[Benny Profane]

Don't even think of an auto with the turbo. And, it will be a new skill learning to handle the turbo in weather.

[Cruiser]

I loved my '06 Subie Forester XT turbo. It was a beast in the mountains and quite civilized around town when the kids were in the car. I lived at ~6K and regularly drove to 10K to ski. No issues to report with altitude. Don't worry too much about keeping the boost up during the lower end of the RPM spectrum. The 2.5L has more than enough pep on its own (I also had a n/a '05 Subie) to keep you rolling when you're not asking it to pull very hard. Pick up a second set of rims with studded snows and you'll be happier than a pig in slop when you take it out into the snow.

Summary: Buy the turbo. Drive like you have some sense most of the time. Drop the hammer every now and then when you need it. Done.

[Dexter Rutecki]

Own the 05 2.5xt also, only driven once above 6k feet, but I've been told turbo is ideal for altitude. Personally I'd prefer the turbo over the 3.0 engine because I think it's slightly more efficient, and output is the same (from what I remember). Granted you have that turbo lag at low RPM's, but it's not something I've ever really had a problem with.

That said, I've had a bunch of issues with axles and struts over the past few months that have cost me close to 3k to fix, so you might want to check that stuff carefully (I know I drive on very rough road surfaces a lot, but still). You'll probably be happy either way, though.

Oh yeah, I'm assuming you're going with manual transmission. If not then go with the n/a engine.

[summit]

My buddy has an turbo Impreza and he loves it in the mountains on the tight corners and slow roads too. He also uses regular gas.

[KeyserSoze]

** I'm assuming that the Subaru turbocharged motors perform dynamic ECU-remapping and wastegate adjustments in response to altitude changes. If they don't, please chime in here and let me know.

I was in the middle of researching this exact issue, and found your thread via google search. I'd always assumed that all turbo cars compensated for reduced atmospheric pressure by increasing boost, but found info that says that is not correct:
http://www.clubwrx.net/forums/high-a...-altitude.html
It's a huge thread, but the gist of it is that subies maintain a constant 'pressure ratio' across the turbo, so that if atmospheric pressure goes down, boost goes down as well in exact proportion, so that a subaru turbo engine loses power output as a function of altitude exactly as a naturally aspirated engine does

Another thread (that didn't sound very authoritative) said that a Mitsu Evo maintains constant boost, partially mitigating the performance loss (relative to a N/A motor) at high altitude. It honestly sounded like the author was pulling the info out of his ass though, so I'm not gonna bother linking to it.

A BMW engineer claims about the 335i

"We have two Mitsubishi turbos running at 0.6bar (8.8psi). These can boost to 0.8bar to compensate for altitude using the two electronically-controlled wastegates," Udo explained.

http://www.eurotuner.com/featuredveh...upe/index.html

So, 3 different car companies, 3 different claimed results. And note that subaru thread is 5 years old, it's possible subaru changed how they do things (or even that it varies amongst models of subarus).

I'm going to keep searching hopefully find actual data of people with a stock subie and a boost gauge who've measured boost at various altitudes.

[sidewall]

That kind of sucks to hear, I was always under the impression turbos compensated for altitude.

[Duffman]

The newer Legacy and WRX turbos do compensate for altitude, so that is not a problem. I have never driven the cars at altitude together, but the 2.5 GT turbo is much more fun than the 3.0L. It has higher power and torque surprisingly, even down near the bottom end. Plus, for driving in shitty weather just keep it out of the boost range by short shifting and no boost surprises. Actually the 2.5L motor has decent low end torque, and the boost comes on fairly early (2500 rpm or so) so turbo lag is pretty minimal. Top end is much better with the turbo, and I imagine the difference would be greater at altitude.

You know what to do....

[KeyserSoze]

The newer Legacy and WRX turbos do compensate for altitude, so that is not a problem.

That's excellent news. Do you know how much altitude they can compensate for (or how many psi/bar of pressure)? I assume they hit a limit eventually, unless the stock turbo is waaay oversized.

[cascadianwarrior]

Buy the turbo. I picked up an '07 Legacy 2.5GT and love it. WA doesn't have the altitude to deal with so no help there. But after test driving both cars (2.5GT & 3.0L) I found that the turbo is just more fun to drive. '07 has thumb shifters on the wheel, paddle shifters came in '08. Even with the automatic, just switch to sportshift and choose 1 of 3 modes to ramp it up and play with the rpm's. Mount up some 17" Blizzaks and you've got a super fun car to rally up the mountains in. I've taken mine to about 125 but I think I remember reading it governs out at 137 or 143; more than fast enough for me. I mainly do in-town driving with one quick trip to my local hill weekly and average 22 mpg, although super unleaded for the turbo does kinda suck.

Do it.

[spicy cha cha]

I haven't a clue what a wastegate is, but I do know test driving the turbo was fun as shit.

it so fun that my driving record, wallet and I made an executive decision not to get the turbo.

[karpiel]

Don't even think of an auto with the turbo. And, it will be a new skill learning to handle the turbo in weather.

There's that too...

Even if you think you have it down like a pro, it can still rape you and eat your children. Think short on ramp, half in the shade so half covered with ice in heavy traffic, you have to be careful.

There's a reason I like my n/a 2.5 4eat for driving in really shitty conditions. I didn't care how fun it was or how much I hate autos when I bought it, I just wanted a snow tank. I've been stuck before, having to dig out because the gearing wasn't low enough in my subaru stick to get moving on a steep grade in snow, even with all seasons I couldn't even make the wheels spin, it just couldn't move. With the auto I just put it in D3 (no overdrive) and take off in any conditions, it never has to downshift on the highway, I never have to take my hands off the wheel and I never have to use the brakes to maintain speed on long steep descents.

Call me a pussy, but I like simplicity while trying to avoid 18 wheelers that can't find their lane and plaster the windshield in an inch of slushy grit that makes the wipers stop dead.

Of course, I'm also the sort of idiot that would leave to drive my grandma to the airport for an international flight knowing I-70 was closed at foot 2.5 of a 5 foot storm, not get stuck once in traffic and make it home after an uneventful but slow 6 hour drive.

[Duffman]

While the SI drive mode selector found on the 08+ model GTs is generally a useless gimmick, it works well for one thing, driving the turbo car in really shitty conditions. Basically, in the I mode, which is actually designed to save gas, the turbo output is halved from 14 psi max to around 7 or 8. This basically eliminates any unexpected boosts such as the lane change described above. Honestly, the people complaining about lag and snap on turbo accel obviously haven't driven the 2.5L. The original 2.0L motor on the first WRX and the JDM legacies is very laggy, but the power delivery from the newer larger displacement motor is pretty linear without too many surprises. And again, since even with the autio, the sportshift gives you full control of all five gears, its easy to stay out of boost all together if you wanted to do such a thing. I had to get the 5EAT auto on my 08 GT due to wife issues with a manual, and between the manual shifter controls, the Stability/Traction control, and the AWD, this thing is an absolute snow tank.

[bngofast]

My .02... Turbos will always be affected by altitude purely from a mechanical standpoint. While various cars may have turbos that are large enough and not being used at their max capacity from the factory to compensate for altitude, there is definitely a tune for all turbos that altitude will affect.


Other than that, I'd get the 2.5 personally. From what I understand from other friends that own these, the auto does fairly well at compensating for any lag if you want to go that route. Seems as though Subaru's done a great job leveling that turbo curve especially for the more luxury models like the Legacy and Outback. If you're conservative and keep it out of the turbo you'll save gas mileage but it's there if you need it to go.

[PNWbrit]

XT outback is a shit ton of fun to drive.

I have the speeding tickets to prove it.

[liv2ski]

Listen to Duffman and Cruiser. I am clueless what Benny is trying to say about not getting an auto with a turbo, as an auto doesn't lose boast when shifting like a MT does. Turbos and AT's were meant for each other. I just insist on a MT, I could give a rat ass if I lose a little boast between shifts. I have also read that a turbo is better at altitude than a NA engine, plus I love a turbo, as it is very easy to mod for extra horsepower. Go turbo 2.5 with a MT if available is my 2 cents.

[sidewall]

My sister has an 04 outback 2.5 and it really sucks in the mountains going down I-70. So I'd go for the turbo. Here's some cool skid plates you can put on as well
http://www.get-primitive.com/

[karpiel]

My sister has an 04 outback 2.5 and it really sucks in the mountains going down I-70. So I'd go for the turbo. Here's some cool skid plates you can put on as well
http://www.get-primitive.com/

Even in my outback with a 2.2 I never had to go slower then 70 up the major hills. She needs to learn to use the gears and keep that 2.5 revving high, you aren't gonna hurt it.

[Chainsaw_Willie]

My buddy has an turbo Impreza and he loves it in the mountains on the tight corners and slow roads too. He also uses regular gas.

What year? AFAIK, "Turbo Impreza" = WRX unless he's done an engine swap in an older model.

Putting regular gas in it is silly. The small savings at the pump could very easily be outweighed by major repair bills for melted pistons if he ever puts his foot to the floor. Maybe he'll get lucky though.

With my current commute I fill my '06 WRX (2.5L + 5 speed) up once a week. The price diff between 87 and 92 is about $0.25/gal on average. When the gauge says 'E' it takes about 15 gal. to fill up. 15x.25= $3.75 more per fill up. If I drive to the mountains on the weekends I'll fill up a couple more times a month. That's about $20 - $25 extra in gas each month. If you can't afford that, probably shouldn't own a turbo.

All I can say is my WRX is a LOT of fun to drive to the mountains. Even with summer performance tires on it I managed to keep it on the road. Now I've got snow tires on it, looking forward to some new snow this weekend.

[sidewall]

Even in my outback with a 2.2 I never had to go slower then 70 up the major hills. She needs to learn to use the gears and keep that 2.5 revving high, you aren't gonna hurt it.

She does, I taught her how to do that, but still it could use a little more grunt.

[stash searcher]

sorry, but i'd agree with benny on this one.. no auto with your turbo subie. don't know what year, but we drove a turbo auto baja for about a year. it sucked. plus, they're too heavy.

can't speak to manual turbos, except we opted not to get one because they have higher chances of breaking in severe cold weather. we got the 2.5RS impreza. we love it. personally, i would have gotten the TS, but i like my back seats to fold down.

as for gas, regular might look cheaper, but i found that my gas mileage increased noticeably when we switched to premium. i think it increased enough to warrant the price difference. and premium is suggested, and i would especially run only premium if i had the turbo version. also, removing our yakima system (for the drag races) increased the gas mileage...
other reasons we didn't get the turbo- costs more to fix, costs almost twice as much initially.
go newer than '04 (?) if you don't want the usual head gasket issues.. i think they changed the heads since then (maybe it was '05?)

[365wp]

Had 98 Outback with 2.5. Now have 2.5 turbo Volvo. Love it. My first turbo car. It's not really any different to drive in poor conditions - you wouldn't put your foot in it anyway, so you don't get into boost.

My friend just got a used Forester XT...wow what a difference compared to the NA 2.5. If my next car is a Subaru, it will have a 2.5 turbo.

You won't regret getting the turbo. You will sometimes regret not getting the turbo.

[Gripen]

can't speak to manual turbos, except we opted not to get one because they have higher chances of breaking in severe cold weather. we got the 2.5RS impreza.

Uhhhh.... say what? How do you figure that??