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Guest Message by DevFuse
 

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Took a test drive in a Forester XT this morning.


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72 replies to this topic

#26 LameRandomName

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Posted 20 September 2003 - 04:57 PM

Excuse me?

I'M getting closer? :-\


Look... I don't need to click on a link to understand how turbochargers work, and I'm not going to sit here and mince semantics with you. Nothing personal, I'm just too old to be playing with my blood pressure like that.


FLOW does not make boost, PRESSURE does, and the more intake pressure you want to make the more exhaust pressure you have to build.

TANSTAAFL

There Ain't No Such Thing As A Free Lunch.

The rate at which pressure builds at any given RPM (Lag) is directly related to the total area between the exhaust manifold and the face of the impeller, which is why small turbos make boost faster and big turbos boost slower.

FLOW is a function of PRESSURE.
The higher the pressure in any given plenum, the more flow though that plenum.
A garden hose at 10psi will flow more water than the same hose at 5psi.

Don't believe me?

Put a pressure meter on the engine side of your turbo and watch the pressure in the exhaust maniold increase in lock step with the pressure in your intake manifold.

#27 Hodaka Rider

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Posted 20 September 2003 - 05:48 PM

Semantics? OK, I guess I'll give you that one. I'm just quoting what I know from the link I posted (atually refered to on the Banks turbo site) and the compiled into I have from turbo experts (Banks, Garrett, etc.) It's all good. They just all seem to treat backpressure as a bad thing, not something that makes power. They also seem to all agree on exhaust flow as being the key.
I can see what you mean by pressure in the manifold (pre-turbo), but I guess that's where we diverge. I have never seen that particular pressure referred to as backpressure. Backpressure is typically used to refer to resistance to flow, not something that actually helps. Manifold pressure is another story all together. Semantics, I guess.
BTW, all of the power engineers I have talked to would refer to it as manifold pressure as well. Maybe it's a difference between USA and Canadian schooling?
:eh:

#28 LameRandomName

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Posted 20 September 2003 - 06:00 PM

Back pressure AFTER the turbo is a bad thing.

You want to have just enough pressure to keep the gases moving, because if you dump them into too big a plenum (exhaust pipe) they'll use up all their energy expanding to fill the volume instead of moving down the pipe and out.

Which is why it's best to decrease the pipe diameter as you get closer to the tail pipe.

(Another application of the same principle can be seen in one of those buildings done in the style where the air conditioning ducts are exposed, like at the mall. Next time you're there, look up and you'll see the pipe necking down as it gets further away from the main junction.)

#29 Hodaka Rider

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Posted 20 September 2003 - 06:16 PM

Back pressure AFTER the turbo is a bad thing.



THIS is something we totally agree on! Fer shure. Too bad more people don't understand that one, even in N/A engines. That and the size of the pipe. Some people are really silly on that one.

#30 Stupidru

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Posted 22 September 2003 - 10:17 AM

I've owned both...turbo manual & auto. The only thing I missed w/ an auto was downshifting into turns...otherwise I THINK their equally as fast....ones faster than the other in different senario's.

#31 wrxsubaru

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Posted 22 September 2003 - 03:30 PM

I would agree that if the auto had the same gear ratios as the manual that the auto would be faster, because of shifting speed. The auto does lose its boast when you shift. Any way the forester maunle has really low gears in the maunle, compared to the auto. Thats why the car you test drove dident feel like a 13 sec car.

#32 LameRandomName

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Posted 23 September 2003 - 12:46 AM

The auto does lose its boast when you shift. Any way the forester maunle has really low gears in the maunle, compared to the auto. Thats why the car you test drove dident feel like a 13 sec car.



Two things...

* The auto doesn't lose boost during shifts. However, I'm not going to argue that point more than I already have.

* The car I drive didn't "feel" slow, it WAS slow and it wasn't because of the automatic tranny.
Folks, you really have to get past your blind worship of manual transmissions.
And the worst automatic in the world won't knock 2.5 seconds off the time of a stick car.

#33 Tiny Clark

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Posted 23 September 2003 - 01:52 AM

They use automatics in dragsters for some reason... maybe because they are basically faster?

#34 wrxsubaru

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Posted 23 September 2003 - 10:44 AM

The point i am trying to make is the gearing diffrences between the auto and manule which is a big diffrence will afect the feel of the car and how fast it is.
Dragsterauto trannies, which arnt alaways used are super built trannies that share little with a typical auto. F1 uses autos, but there not like the one in my moms legacy.

#35 LameRandomName

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Posted 23 September 2003 - 12:33 PM

The point i am trying to make is the gearing diffrences between the auto and manule which is a big diffrence will affect the feel of the car and how fast it is.

Do you understand that I am talking about a two and one half second difference?


Dragsterauto trannies, which arnt alaways used are super built trannies that share little with a typical auto.
There are a number of different transmissions used in drag racing because there are dozens of different classes.
The most common transmissions in drag racing are in the Bracket classes, and THOSE actually are regular street transmissions modified for higher horsepower applications.


F1 uses autos, but there not like the one in my moms legacy.
This has nothing to do with F1, or for that matter the NHRA.
This is about a car that is SUPPOSED to run in the high 13's but actually drove like a 16 second car, and there is no way in HELL that an auto tranny is going to acount for that much difference.


I am perfectly willing to believe that there was a problem with THIS PARTICULAR car, but the notion that "it felt slow because it was an automatic" is really just too stupid for words.

I've been drag racing since the Reagan administration and i was running a 9 second camaro back when you could still buy a new Brat off the showroom floor.

I'm TELLING you that this car was SLOW. Period.

#36 wrxsubaru

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Posted 23 September 2003 - 11:27 PM

I can belive that the problem with the forester was something other than the trannie, but when my dad test drove the Wrx it wasent that fast, with the auto, but with the manule it faster, not 2.5 secs faster, but faster.

#37 LameRandomName

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Posted 24 September 2003 - 12:20 PM

Next year, when I'm ready to buy one, I'm going to do another test drive, of both.

Thing is, if the auto in a properly tuned car is still slow like that (although I don't expect it to be) I wont buy one.

I have discovered that the manual version does NOT do as well in the snow as the auto.

The 50/50 split that you have with a stick is inferior to the variable split the auto has and tends to make the rear end want to come around for a visit, especially in fresh snow.

And since I'm a skier....

#38 wrxsubaru

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Posted 24 September 2003 - 01:11 PM

the auto goes to a 50/50 split when a wheel spins, and when the car is in first, and maybe second gear, first gear for sure.

#39 LameRandomName

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Posted 24 September 2003 - 01:32 PM

Does it really?

Well, learn something new every day.


The only thing I know for sure is that when a friend and I tested our Foresters on a snowy day last winter, after switching back and forth between cars we both agreed that the auto did much better in the snow and that the stick car (mine) was much more prone to swinging out.

#40 MilesFox

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Posted 25 September 2003 - 12:17 PM

ok, i am going to end this right now. first off, these are subarus. subaru designed this little solenoid that keeps the drop in intake pressure from slowing up the turbo between shifts.

and i will tell you what, i put a 5spd in my 90 hp ea81 turbo to replace the rump roast-o-matic.
i dumped the clutch ans spumn all four tires in 4wd hi in 2nd gear! and thats only because i thought it was in 1st low!

and the automatic wouldnt even let the tires break free in mud.

you dont see an automatic in the rally car? autos in subarus were an afterthought. my buddy had a 2.5 rs(non turbo) and the auto really wouldnt let its rpms do their things. its like subaru put automatica in as an after thought, so that people who coulndt drive a stick would actually buy one!

NUFF SAID!

#41 Stupidru

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Posted 25 September 2003 - 01:58 PM

APPLAUSE!

#42 BlueSoob

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Posted 25 September 2003 - 02:03 PM

I'm going to have to throw in a few cent here, since the discussion has come down to the pros/cons of MT vs AT.
Though I have to admit to being a seasoned Auto driver and only a fresh 5spd driver. I learned this past winter that the Manual 4wd and the control of the gear shift allowed me to drive and stop safely on two flat tires on sheet ice on the freeway.
I will also proudly brag that I received commendation from the Oregon State Patrol for the control that I had over my car and the skill that I exhibited at pulling it over. This was as we sat at the bottom of a hill watching people fly off into the snow fences.
The difference in the "AWD" systems in the AT/MT was something to get used to. But as I have found it comes down to the skill of the driver.

#43 mtsmiths

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Posted 25 September 2003 - 02:35 PM

I have owned well over 100 cars in my admittedly long life. (Prolly closer to 200 if you count the 'flips' that never got registered).

Much of it my driving has been in snow country, high Sierras, mountains of Arizona and New Mexico, N/W Montana (and all the surrounding states and Canada), hell, even in fresh fall on the top of Mauna Kea, in Hawaii.

I have owned 4WD Jeeps, Power Wagons, Toyota FJ, and all three generations of Subarus ('78, '87 (2), '00). I've owned stick and auto versions of each, except for the Power Wagon, which was a '51, and the FJ, which was a '67. Company 4WDs driven in LOTS of snow include Dodge Rams, Durangos, and several Fords (all autos). I've driven on black ice and in unplowed snow that came over the hood.

I will state uncatagorically that, IMHO, an auto beats a stick in snow driving, hands (and clutch foot) down. The power delivery is smoother, more even, and it's far easier to keep the torque transfer down. The LAST thing you want to do in snow is spin your wheels. The ONLY thing a stick beats an auto for is rocking out of a hole, and I take that back unless it's a 3-on-the-tree for straight low/reverse rocking (the gates just don't line up on most four and five speeds).

Now, having stated my vitae, I will additionally state that the BEST snow car I have ever driven is our '00 Legacy wagon with studded tires, after that it was my son's '88 4EAT turbo wagon.

We can always get out of our driveway, no matter how much snow with the GLs, but the AWD just ignores snow. Low and second lock in the 50/50 split which we use around town and in really deep sh!t, but I've driven the Lagacy in 18" of unplowed snow (first over the St. Regis to Paradise part of Lookout Pass during a fresh fall) in [D] at a steady 45 - 50 mph and it felt like it was on dry pavement. Only problem I had was having to stop every few miles and scoop the snow dam off the front so the headlights could shine.

If you are serious about getting-around-driving, as opposed to 'playing' (notin' wrong with THAT, mind you) get an automatic.

#44 MilesFox

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Posted 25 September 2003 - 04:40 PM

i guess it comes down to personal preference.
but i think that a stick is best in snow. thats because you have more control of the power to the wheels.
sometimes you want to break an wheel free to maneuver a turn, such as kicking the rump roast end out when the car wants to understeer off a curve.

my 2 cents

i never ran my pinto off the road in the snow, and being a stick let me kixk the rump roast out whenever necessary. sometimes wheelspin is what will get you through. and at least with a stick, you have full control of your wheelspin, if thats what you want.

autol blow!:headbang:

#45 99obw

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Posted 25 September 2003 - 05:30 PM

Basically pneumatics at a simple level operate the same as electricity, so I will make an electrical analogy. This is a huge simplification but should be roughtly accurate.

Behaviour in a pneumatic system can be described by the pueumatic equivalent of ohm's law, where flow equals pressure devided by resistance. Ohm's law is I = E/R where I = current(flow), E = voltage (pressure), and R = resistance. The power dissipated can be written as P = IE, P = E^2*R, or P = I^2*R. Therefore in a pneumatic system the power dissipated can be thought of as roughly equal to flow times pressure drop (P=IE). The power dissipated in the system would be roughly the same as the power(HP) delivered to the turbine.

The system isn't really that simple though. The turbine dissipates power by compressing the intake gasses AND stores energy in the rotating mass, but you get the idea.

Backpressure after the turbo limits turbo performance by dropping the pressure elsewhere than the turbo.

Hope I am making sense.

#46 99obw

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Posted 25 September 2003 - 05:38 PM

As for the best AWD/tranny combination, my 86 Tercel sr5 with 6 speed manual tranny and 50/50 torque split would run circles around my 99obw with an auto trans. Not to mention that the manual never shifts when you don't want it to and break the tires loose. I can also shift a manual smoother than any auto does, eliminating the unpredictability of auto trans shifting on extremely slippery surfaces.

The tercel did like to kick the rear around, but I preferred that to the absolutely scary understeer of the obw.

#47 LameRandomName

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Posted 25 September 2003 - 05:53 PM

I was back at the dealership today and i was talaking with the mechanics about this.

They confirmed that when those cars first arrive they are not "set up" properly and they have to go through a process that includes an adjustment to the computer program that lets the car make proper power.

I gather they keep it in a "limp home" mode of some type.

Why?

I don't know. I could speculate, but so can everyone else so I wont bother.

So it's NOT the automatic transimission.



And miles...
I know you THINK that what you posted is some sort of conclusive proof of something, but all it proves is that you're likely to go through parts quickly.

And the auto was an afterthought?
Puhleeez. :rolleyes:


NUFF SAID

#48 1ABAJA

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Posted 26 September 2003 - 02:17 PM

After driving the "Trash Wagon 6" around for the last couple of weeks, I would have to say that it would not be the same vehicle if it were an automatic...in fact, I am hoping to blow Miles Fox off long enough to be able to drive this bad boy in snow:D

(5 speed MNL + 4WD)*SUBARU = BLISS
...of course the BLISS would have to be relative to the (HP)

Josh!

#49 MilesFox

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Posted 30 September 2003 - 10:26 AM

Originally posted by LameRandomName



And miles...
I know you THINK that what you posted is some sort of conclusive proof of something, but all it proves is that you're likely to go through parts quickly.

And the auto was an afterthought?
Puhleeez. :rolleyes:


NUFF SAID


yo! lets see your dirty hands! lets see your "World's Only Subaru 2-door Wagon"! Lets see your Ea81 body with ea82 motor, suspension, and transmission, lets see your ported and polished heads, lets see your krylon paint job, sheetmetal body armor, and 6 inch lift!
Lets see your ea81 in an ea82 body with spfi. lets see your ea82 water pump on an ea81 motor. lets see your 2wd 5spd to 4wd 5spd, your 4wd auto to 4wd 5spd, and 2wd auto to 4wd 5 spd.

no? thats what i thought! HEY< i know these things from DOING, not collectively listening to whoever. and you called me out?
"IF YA GOTTA PROBLEM LETS TAKE IT OFF ROAD" (which shows i know how to drive, too:moon: )

"I AM MILES FOX!"

#50 cookie

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Posted 30 September 2003 - 12:20 PM

caffine Miles.




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