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Old 07-12-2001, 11:30 PM   #1
RaceCarRiot
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Question top speed?

this is kinda silly, but...what's the top speed of a stock 5-speed 1.8L impreza?

i did some impromptu high speed umm...err..."testing" (dont' ask) on the way home tonight and had it up to 100+ and still had a bit more throttle to go...i'm sure if i had the windows up, it would have helped the top speed a bit, but the whole event was unintended...

needless to say, 'ol bluey will probably be getting an oil change 500 miles early for all the abuse she suffered tonight...

(adam)
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Old 07-13-2001, 12:23 AM   #2
STiTuner
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SCC tested and apporved.

throw the car in 5th gear and cruise along at what ever RPM it is half way to red line. (ie redline = 6500 drive at 3250 RPM) and take your speed and time it by two. I think thats how it goes

Brad
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Old 07-13-2001, 10:22 AM   #3
Tkacik
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I have had mine to 115. 95 1.8 AWD.
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Old 07-13-2001, 10:47 AM   #4
Layman
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STiTuner,

There's no way that equation works. With that kind of logic, we should be hitting about 140 stock (actual, not inticated).

The faster you go, the more difficult it is to gain any more speed. At high speeds, increasing top speed becomes less about horsepower and more about aerodynamics. It's not a direct ratio of RPMs, gearing and HP. There's a parabolic curve to increasing top speed which, when you consider, makes the top speed of the Corvette, 911 and other such cars all the more impressive.
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Old 07-13-2001, 11:19 AM   #5
ylexot
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Actually STiTuner is correct...sort of.

It's all about hp AND aero. You need the hp to overcome the aero. As Layman said aero forces increase exponentially with speed (to the second power). Power required to overcome the speed is also an exponential function (to the third power).

However, if the car has enough power to overcome the aero at redline, STiTuner's equation is correct. The gearing is fixed and the engine RPM/wheel RPM is a linear function.

The real question is does a 1.8L Impreza have enough power to overcome the aero at 140mph...I seriously doubt it. I have heard people say the 2.5 maxes out around 130. Of course the RS has all the scoops and wing to increase it's drag.

Micah
B.S. Aerospace Engineering MD '98
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Old 07-13-2001, 11:33 AM   #6
Layman
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Right. Sorry about that - I should have specified that I was talking about that equation in reference to the RS.

I would suggest that the only time that equation would hold true would be in a car with a ton of torque and a low geared top speed. Even the Vette doesn't actually hit the top speed that it's geared for.

This is why, for some cars, the top speed is acheived in 4th gear (or 5th on a 6-speed) due to the greater availabilty of torque at a given RPM.
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Old 07-13-2001, 02:26 PM   #7
Giova
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I hit 6k RPM in fifth gear in my 2000 RS

Last edited by Giova; 07-13-2001 at 03:56 PM.
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Old 07-13-2001, 04:35 PM   #8
SubyRacer
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i got mine up to 124mph @ 4900rpm in 5th, didnt have much pull left at all. the gearing is very tall in this car.

disclaimer: long stretch on highway, middle of night, literally NO traffic, yadda, yadda, yadda. but i still wouldnt do it ever again. car wants to fly off the ground after ~115.
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Old 07-13-2001, 05:02 PM   #9
Iowannaski
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Quote:
Originally posted by Giova
I hit 6k RPM in fifth gear in my 2000 RS
If your fifth gear is the same as my fifth gear, that's ~135 mph. Wow. So what have you done to your engine to get that kind of hp?
(oh, and drag increasing with the cube of speed isn't really an exponential increase, but I don't think it's called a cubal increase either ....forget it)
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