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Insane speed in german cars... slightly OT, had to share...
Hey Dave,
Larry is right. Weight has virtually nothing to do with top
speed. It's not a factor in the equation at all other than in the rolling
resistance of the tires, which increases proportionally to the weight. At
highway speeds, though, the rolling resistance is almost negligible; the
primary resistance is air.
>I would say that weight has quite a bit to do with it. Put that 450hp motor
>into a Freightliner and I don't think you'll be hitting 100mph!
Of course not - but that's due to the aerodynamics, not the weight. Put 2
identical 16V Sciroccos next to each other, put 4 (obviously masochistic)
obese people and luggage in one, and a 100-lb chick in the other. Their
top speeds will be identical. Sure, it'll take the overloaded one longer
to achieve that speed, but they will both top out at the exact same speed.
In fact, the heavier car might be slightly faster due to the fact that
it'll be riding on the bump stops with that much weight -- less height
equals less overall wind resistance.
> As far as
>the gearing, etc. I realize that hp and drag are the biggest two factors but
>weight does have it's place also. Another thing is that even though vipers,
>corvettes, ferraris, etc etc. don't show factory numbers of 190 to 200mph,
>don't think that they never get there!
They don't get there! I don't trust manufacturers' numbers (nor should
you), but I do trust Car & Driver's top-speed numbers. They run the cars
until they don't accelerate any more...
A typical car will reach 99% of its terminal velocity within about 90
seconds. That last 1-2mph might take another minute or two.... but you're
not going to suddenly gain 30mph by keeping your foot in it.
And the claims of an RX-7 at 180mph are absurd, as are a 150hp Rabbit
attaining 140mph... Plug in the dyno numbers from a VR6 into a Scirocco
(using VR6 gear ratios of course), and you'll still only see 137mph in a
Scirocco.... with a Cd of 0.38 vs the Rabbit's 0.44.
Plug in that Cd (0.44) and the top speed of a VR6 Rabbit calculates as
129mph. With a 172hp, all-top-end VR6! You'd need a turbo VR6 just to get
close to 140mph in a Rabbit! In fact, if you bump up a VR6's entire torque
curve by 25% simulating a large turbo running low-boost to put out 215hp at
the motor, you'd see 141mph as a top speed.
>I would say that with a little
>tweaking (especially on the U.S. cars) that it could be achieved.
I'd say you'd need a *lot* of tweaking to get just about any car on the
road to 180-190mph. (FWIW I consider an aftermarket turbo kit to be a
"lot" of tweaking! -- Especially on something like a Ferrari.)
>How much
>difference does a turbo make on our little motors? sometimes 100% increase
>in hp? More? Don't you think they have aftermarket kits for some of the
>world's super cars? Plus, I would say that 350hp to 450hp is the norm for a
>super car.
Well, to put it in perspective, I hit the 166mph speed limiter in an E46
BMW M3 last year on an Autobahn. The customer had M remove the 250km/h
limiter, but one remains at 268km/h. This is a 3400lb car with a Cd of
0.29 and a 343hp, 8200-rpm 3.2-liter inline 6. It hit the limiter with
some authority, but I'd say it would have topped out at around 172 or
so. So yeah, a turbo would easily boost this car up into the 180s or 190s.
> Where do you get this stuff
>anyway--weight and time have nothing (or virtually nothing) to do with top
>speed??
Time: Time has nothing to do with top speed because you assume time is
infinite when measuring top speed. You keep your foot on the floor until
(a) a limiter kicks in or (b) the car fails to accelerate any more....
whether it takes 10 seconds or 10 minutes. Therefore time is moot.
Weight: Explained above. It slows acceleration, but has very little
effect on top speed.
Jason
PS: The calculated top speed for Josh's 1.8T Scirocco, putting 257hp to
the wheels is 157mph. What everyone seems to forget in making outrageous
top speed claims is that the power needed to combat wind resistance is
exponential. The additional 180 or so horsepower that Josh has over a
stock 1.8 16V Scirocco only got him 33 extra mph. That has nothing to do
with the Scirocco's (low) weight -- only aerodynamics. And by the way,
from 0-157mph would take only 49.3 seconds. :)
PPS: Do you think a Scirocco's windshield would actually survive 157mph?
>Brando-
>(how do I remove the background??)
>Weight has virtually nothing to do with top speed..only horsepower and drag
>count in this equation.
>That also leaves out gear ratio to the extent that you can be under-geared
>and be rpm-limited, but gearing up (lower numerically) doesn't not assure
>more top speed. Once optimum gearing is found (based on hp and drag), going
>up on the gear slows the car down.
> Top speed is top speed; the definition is "maximum speed achievable".
>Having 30 minutes to get there does not add to a car's maximum speed
>achievable. (and we are debating the issue of a car's...any car's...top
>speed here, right? I want to make sure we are both talking about the same
>thing )
>Peace.
>
>Larry
> ----- Original Message -----
> From: Brandon Smith
> To: L F ; SCIROCCO-LIST
> Sent: Monday, November 04, 2002 9:00 PM
> Subject: Re: Insane speed in german cars... slightly OT, had to share...
>
>
> power to weight ratio and gear ratios make up for some of that. Plus the
>sight didn't say how long it took to get to that speed. I could have taken
>them 10 minutes to get up that high for all we know.
>
> -Brando
>
> ----- Original Message -----
> From: L F
> Sent: Monday, November 04, 2002 8:16 PM
> To: Rabbit16v; Scirocco List
> Subject: Re: Insane speed in german cars... slightly OT, had to share...
>
> The new Viper makes 500hp.
> It's top speed is 190mph (est).
> You are saying a MK4 makes at least 500hp?
> I dunno', I'm asking.
>
> Larry
>
>
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