LOwest RPM in 55MPH, 60MPH or 100KPH
Hong Wai Chin
or 100KPH( for Canadian folks )? My 90 Mitsu Mirage 3 speed Automatic has
2500RPM at 75KPH, 3000RPM at 90KPH(50MPH) and 4000RPM at 110KPH(68MPH).
Is lower RPM at higher speed good? Is it related to the car's horsepower?
transmission?( since manual trans. has lower gear ratio and thus lower
RPM than automatic trans. )
Fred ch...@fornax.UUCP
ch...@cs.sfu.ca
Randy Brown
>Hi netters, What car that you have driven has the lowest RPM at 60MPH?
>My 90 Mitsu Mirage 3 speed Automatic has 3000RPM at 50MPH & 4000RPM at 68MPH.
My '83 Z-28 does 2000 at 55MPH, about 2500 at 70MPH.
>Is lower RPM at higher speed good? Is it related to the car's horsepower?
>transmission?( since manual trans. has lower gear ratio and thus lower
>RPM than automatic trans. )
Sure, lower rpm is good, since you get better gas mileage, less engine wear,
less pollution, ... It is not related specifically to the engine's
horsepower, but the engine must be turning fast enough to produce enough
horsepower to maintain the forward motion of the car at that speed.
Your car probably has a 4-cylinder engine, which usually requires higher rpms
to produce the same hp as an 8-cylinder (as a generalization). Of course,
people will flame me and say "but turbos, but FI, but superchargers, but
4 valves per cylinder, but but but".
The transmission and rear gear ratio will determine what speed your engine
turns at a given road speed. I have a 5-speed manual, and fifth gear really
drops down the rpms. If I had a higher rear-end gear ratio, my engine would
turn faster all the time, regardless of what gear I am in.
Hope this helps.
>Fred ch...@fornax.UUCP
> ch...@cs.sfu.ca
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Michael Perry
1984 Isuzu PUP Diesel 5 speed -> 2500 @ 55MPH
1990 Nissan Maxima GXE 4 speed auto -> 2200 @ 55MPH
JOSEPH T CHEW
Okay. Here we go. Call the fire department, because this net contains
several people who _know_ what they are talking about (I'm just guessin').
Every car requires a certain horsepower to move at a given speed.
This is determined by the rolling resistance of the car and by the
air resistance. To simplify things, we'll ignore drivetrain losses
and accessory loads.
Each engine is characterized by a power curve of horsepower vs. rpm.
The curve represents the maximum power that the engine can generate
The shape of this curve is not clean and simple, nor are the factors
affecting it, but these issues are also beyond the scope of this posting.
So just imagine a bulbous, more or less flat-topped, monotonic curve
that starts at (0,0) and flies apart, like your rod bearing caps, at
the redline.
The other key fact is that an engine turning at a given rpm is not
necessarily producing the maximum power that it could at that rpm.
At 4000 rpm in neutral, it is producing less power, and using less
energy, than at 4000 rpm in gear moving the car down the road. In
other words, the space _under_ the curve is also a valid operating
regime for the engine.
For a given speed, the most economical gear ratio is the one that
puts your engine at the leftmost point on the curve at which the
required horsepower is produced -- that is, the lowest rpm.
Another way of looking at the problem is, "What is the top speed
in gear?" In the low gears, you can't reach top speed because
the engine hits its redline. In higher gears, things get better
because you are turning more and more of your engine's power
into road speed without exceeding the redline. But the faster
you go, the more power it takes to go fast (aero resistance).
Eventually you try to poke your nose through the power curve and
that's the top speed.
It is not uncommon for cars to have their top speed in, say,
fourth gear -- fifth being a very tall economy gear for normal
highway cruising, where you aren't trying to accelerate and
fuel economy dictates that you avoid both high revs and hard effort.
The catch, of course, is acceleration. If you were actually at
the most-economical point described above, you would be cruising
at equilibrium, with nothing left over for acceleration. The
transition into one's first economy car usually involves an episode
of public humiliation when you forgetfully try to pass without
downshifting.
Usually the top gear is selected such that, at typical cruising
speeds, you're just a bit below and to the right of the optimum
economy point. This keeps people from REALLY lugging their
engines and/or getting caught with their pants _clear_ down
around their ankles when they pull out to pass.
The original poster asked about a Mitsu Mirage with a 3-speed
automatic. The only Mirage I ever drove had a 5-speed stick --
with that little engine, three speeds seemed like too much of
a compromise. I'd guess that a Mirage with 3-speed auto is
targeted at the around-town market, so one of the logical
compromises would be a top gear that keeps the engine wound up
like a mad hornet at highway speeds.
If I've made a fool out of myself, feel free to correct this posting.
--Joe
"Just another personal opinion from the People's Republic of Berkeley"
Peter Tapscott
Porsche 944 Turbo 1986: 55MPH = 2000 RPM
Approximate top speeds in gear:
1: 40MPH
2: 70MPH
3: 105MPH
4: 135?
5: Who knows?
2000 is the lowest useful RPM in this car. If RPM
gets below 2000, you have to downshift. 3000 RPM is
about the lowest RPM where you can upshift. 6000 RPM
is much more exciting, however.
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| pe...@versatc.VERSATEC.COM -OR- {ames|apple|sun}!versatc!peter|
| Peter Tapscott - Xerox Engineering Systems, Versatec Products |
| 2805 Bowers Avenue, Santa Clara, Calif (408)982-4235 |
Kevinh
Jim Conrad
But didn't my old 85GT lug along at 1600 RPM in the 5th gear?
Ah... but top speed in 1st gear goes to the old 71LT1 vette. It was around
65mph. Think about it: Today, the LT1 can only be legally red-lined in 1st
gear. Sigh.
JimC
Josh Sirota
>Ah... but top speed in 1st gear goes to the old 71LT1 vette. It was around
>65mph.
The Testarossa that I drove a couple of years back could do somewhere near
100kph (about 62mph) in 1st gear. It's that give-or-take a few MPH ... it
came up so fast that I didn't notice *exactly* how many ... I just thought
I'd better shift before I blew up that motor!
Josh
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Sun Microsystems UUCP: ...!sun!eng!jss
chuck smith
>I can't believe the Mustang GT folks are leaving this challenge unanswered.
>But didn't my old 85GT lug along at 1600 RPM in the 5th gear?
According to Road & Track, with the 3.08 gear, turned 1620 rpm at 60mph.
With the base 2.73, it would turn about 1440 rpm. The only thing that would
possibly run lower would be a vette with the new 6spd. Redline in 6th at
290 mph? A slight case of over-gearing. What fun it would be in my Camaro,
combined with a 4.88 in back.
>Ah... but top speed in 1st gear goes to the old 71LT1 vette. It was around
>65mph. Think about it: Today, the LT1 can only be legally red-lined in 1st
>gear. Sigh.
Top speed in first gear is just a matter of the rear-end and first gear ratio.
What ratio did that LT1 have? With different rears, it would do considerable
less. My '68 Camaro, letting the auto shift for it self, shift into second at
about 60 mph. With the high rev capability of the LT1, it would do at least
70. Of course its a dog until about 25-30mph, then look out.
>JimC
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chuck smith |_|_| live long and prosper,
cws...@uiuc.edu | | | or go insane trying.
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Donald P Perley
One of the car mags a few years ago featured a center spread on an old car
made with a drigible engine. The exact figures may be a little off, but
I seem to recall 21 liters, 750 rpm at 100 mph. Redline was 1300 rpm.
-don perley
Thomas Cohen
>j...@hpdmd48.boi.hp.com (Jim Conrad) writes:
>>I can't believe the Mustang GT folks are leaving this challenge unanswered.
>>But didn't my old 85GT lug along at 1600 RPM in the 5th gear?
>According to Road & Track, with the 3.08 gear, turned 1620 rpm at 60mph.
>With the base 2.73, it would turn about 1440 rpm. The only thing that would
Although it's probably out of the bounds of the competition, the
Metallurgique Maybach (or Maybach Metallurgique) pulls 9mph / 100 rpm
in top (third) gear. This gives about (fiddles needlessly with xcalc)
666 rpm or so at 60 mph. And it will probably pull redline in top gear
(1350 rpm) which would be about 120 mph.
Of course it does have a 21 litre 6 cyl, ex-Zeppelin aero-engine in it.
>>Ah... but top speed in 1st gear goes to the old 71LT1 vette. It was around
>>65mph. Think about it: Today, the LT1 can only be legally red-lined in 1st
>>gear. Sigh.
I heard that a 427 Cobra would pull 80mph in 1st. Dunno what the diff
was, or what top speed would be (even with the barn door aerodynamics).
>Top speed in first gear is just a matter of the rear-end and first gear ratio.
True. The Cobra mentioned above would not have done the 0-100mph in the
much touted 8.5 seconds.
> chuck smith |_|_| live long and prosper,
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"Anyone who never makes a mistake never learns |ACSnet: th...@softway.oz
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that" Doug Nye |Internet: th...@softway.oz.au
Al Peterman
>
>Although it's probably out of the bounds of the competition, the
>Metallurgique Maybach (or Maybach Metallurgique) pulls 9mph / 100 rpm
>in top (third) gear. This gives about (fiddles needlessly with xcalc)
>666 rpm or so at 60 mph. And it will probably pull redline in top gear
>(1350 rpm) which would be about 120 mph.
>Of course it does have a 21 litre 6 cyl, ex-Zeppelin aero-engine in it.
As long as we are going to extreme machines, my stock Cardinal RG does
about 170 mph at 2500 RPM and about 80 mph at 1000. I suspect the
ultimate figure would be some of the last WWII fighters. Their large
props were limited to about 2000 RPM and that was good for about 450 mph!
And that's in FIRST GEAR!
--
Alan L. Peterman (503)-684-1984 hm
a...@qiclab.scn.rain.com
It's odd how as I get older, the days are longer, but the years are shorter!
JOSEPH T CHEW
>about 170 mph at 2500 RPM and about 80 mph at 1000.
But any teenager in a Camaro can smoke you on a road course with
enough overhead power lines! :)
I suspect the
>ultimate figure would be some of the last WWII fighters. Their large
>props were limited to about 2000 RPM and that was good for about 450 mph!
>And that's in FIRST GEAR!
I had the impression that the air racers built from them _postwar_ could
scare 500 mph. There seem to be two approaches: a sleek Mustang- or
Tempest-like object with an over-amped vee engine, or something like an
F8F Bearcat fuselage hanging for dear life onto the back of a "corncob"
radial like an R-3500 from a 50s airliner. (In fact, something scratches
the back of my mind about 480 from a stock Bearcat. For those of you
clinging to the illusion that this is an automotive net, a Bearcat was
sort of the ultimate prop-driven fighter, barely too late for WW II combat
and obsoleted almost immediately by the jet age.) I think the limiting
factor (he said as thin ice crackled underfoot) is prop-tip speed. Props
don't like to go supersonic.
Just for marginal relevance, some of these kinds of engines showed up
in Bonneville-type cars (land-speed machines, not Pontiacs) before that
endeavor turned to jets and rockets.
David Binderman
>In article <24...@fornax.UUCP> ch...@fornax.UUCP (Hong Wai Chin) writes:
>>Hi netters, What car that you have driven has the lowest RPM at 60MPH?
In the UK, try a 2.8i Ford Capri. 2700 rpm @ 70 mph, 3700 rpm @ 100 mph
and tops is about 135 mph.
So at 60 it will do 6 * 2700 / 7 rpm, or about 2400 rpm.
'Course, I drive a Toyota MR2 - a car about as practical as a chocolate teapot.
Ob. Advert:
Ever driven at 200 kph (125 mph)
and had some guy right behind you flashing his lights at you
to get out of the way ? - visit Bavaria now !
Regards
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Berkshire RG12 4FZ, UK 0344 850489 d...@siesoft.co.uk uunet!mcsun!ukc!siesoft!dcb
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