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rpm vs. speed question



 
 
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  #1  
Old April 20th 06, 02:13 PM posted to rec.autos.makers.mazda.miata
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Default rpm vs. speed question

I've recently acquired a 05 MazdaSpeed Turbo, 6-speed, a retirement
gift for myself. Love it so far. It's been 40 years since as a single
guy I drove a '64 Vette 4-speed. My driver for the last 13 years has
been a 6-cyl '93 T-Bird auto transmission. Now the questions. At 60mph
my Mazda is turning exactly 3000 rpm in 6th gear. My old T-Bird loafs
along at 1750. Both have roughly the same hp. My 300 hp V-8 Corvette,
with a 308 rear end turned about 2750 in 4th if I remember right.
Anyone know a good source for the relationship between rpm, highway
speed, horse power, number of gear speeds, etc. How can that old Ford
engine cruise along at 1750 when it takes the MX-5 3000 rpm? Why do I
need 6 gears in the Mazda when 4 worked fine in the Corvette? I
probably knew all these answers 40 years ago, but I need a refresher.

Ads
  #2  
Old April 20th 06, 02:57 PM posted to rec.autos.makers.mazda.miata
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Posts: n/a
Default rpm vs. speed question

In article .com>,
"laocmo" > wrote:

> Anyone know a good source for the relationship between rpm, highway
> speed, horse power, number of gear speeds, etc.


There's no precise relationship. It's simply the choice of gearing,
presumably matched to the car's intended use, but also affected by
marketing and fashion. The Miata doesn't start to make serious power
until it reaches 4000 rpm; it also will run all day above 6000 without
problems. It's how a small engine delivers good performance, which the
factory assumes the buyer will value over quiet cruising. The Miata
doesn't have much oomph down low, and more transmission gears makes it
easier to stay within the narrower powerband.

OTOH, modern Corvettes have 6 speeds, just because it's fashionable.
They could probably get by with two.

--
Lanny Chambers
'94C, St. Louis
http://www.hummingbirds.net/alignment.html
  #3  
Old April 21st 06, 12:59 AM posted to rec.autos.makers.mazda.miata
external usenet poster
 
Posts: n/a
Default rpm vs. speed question

In article .com>, "laocmo" > wrote:
>I've recently acquired a 05 MazdaSpeed Turbo, 6-speed, a retirement
>gift for myself. Love it so far. It's been 40 years since as a single
>guy I drove a '64 Vette 4-speed. My driver for the last 13 years has
>been a 6-cyl '93 T-Bird auto transmission. Now the questions. At 60mph
>my Mazda is turning exactly 3000 rpm in 6th gear. My old T-Bird loafs
>along at 1750. Both have roughly the same hp. My 300 hp V-8 Corvette,
>with a 308 rear end turned about 2750 in 4th if I remember right.
>Anyone know a good source for the relationship between rpm, highway
>speed, horse power, number of gear speeds, etc. How can that old Ford
>engine cruise along at 1750 when it takes the MX-5 3000 rpm? Why do I
>need 6 gears in the Mazda when 4 worked fine in the Corvette? I
>probably knew all these answers 40 years ago, but I need a refresher.


I agree with everything Lanny said. But the simplest relationship
might be: smaller engine, higher rpm's.

Engine torque is pretty much proportional to displacement (not
considering force-induction engines which effectively multiplies
displacement). So to make the same power which equals torque*rpm,
they have to spin faster.

If all else is the same with a car (weight, size, etc, which
obviously it isn't here), it will take the same power to drive any
given combination of speed and road grade. Thus the smaller engine
must turn higher rpm.

Now, in your case, it is force-induction, and makes a fair amount of
torque. And its in a small car. So it should be able to be geared
longer and turn lower rpm than 3000 @ 60mph. Lanny is correct that
Mazda however chose to keep the rpms high in consideration of the
sporting nature of the car. Also, it helps mask turbo lag.
Basically, it makes the car more responsive, but at sacrifice of
noise, fuel economy, and potentially some engine life. Frankly,
especially given it is a 6-speed, I would have much preferred if
Mazda made 6th much taller.

Another reason why a manual might be geared shorter than an
automatic is for perceived drivability. Imagine if it turned
2000rpm at 60. You press on the pedal ... nothing. You have to
downshift. And automatic would do that for you, uh, automatically.
Thus perceived better drivability.

And, as Lanny also said, 6-speeds are in vogue. A Corvette, or any
similar torque-monster, simply doesn't need them. Lexus is coming
out with an 8-speed automatic. Why? Because MB has seven!

Oy.


Anyway, enjoy the car. If the noise gets to be a hassle on a
highway cruise, do what a lot of us do: earplugs.
  #4  
Old April 21st 06, 01:17 AM posted to rec.autos.makers.mazda.miata
external usenet poster
 
Posts: n/a
Default rpm vs. speed question

The key de terming factor in the gearing of an engine is the torque
the engine produces.

Push rod V 8 engines are designed to produce high torque, partly
because the push rod design limits the design to 2 valve per cylinder.
This design, while economical, limits the rpm that the engine can
turn. They usually red line at relatively low rpm (5000 to 6000 rpm)

Modern fours, using overhead cams can uses three or four lighter
valves with better modern spring, can turn 7000 or 8000 rmp. But
since the are smaller displacement they produce much lower torque.

The formula for horsepower is:

Horsepower = torque * revs/minute * minute/60 seconds * 2*pi * 1/550
Horsepower = torque * revs/minute * 1/5252

In a very simple way:

Suppose your car requires 100 hp to move along at 90 mph.

A v-8 rated at 300 ft-lb at 2000 rpm will be producing 114. An
engineer will pick the gearing and rear end to produce the right rpm
at the wheels.

A smaller 4 cylinder engine, producing 140 ft-lbs or torque would have
to turn nearly 4300 rpm to produce the power necessary to move the
same car at the same 90 mph.

As for the gears, the turbo engine puts out 28 % more power than the
normal engine, but the full turbo pressure does not kick in until 4500
rpm. the red line is at 6500, so the maximum power band fairly
narrow. If your gears are too wide, you can fall off the power band
when you up shift, so having more gears allow you to keep the engine
turning at high rpm while you accelerate. (its also more fun)



On 20 Apr 2006 06:13:29 -0700, "laocmo" > wrote:

>I've recently acquired a 05 MazdaSpeed Turbo, 6-speed, a retirement
>gift for myself. Love it so far. It's been 40 years since as a single
>guy I drove a '64 Vette 4-speed. My driver for the last 13 years has
>been a 6-cyl '93 T-Bird auto transmission. Now the questions. At 60mph
>my Mazda is turning exactly 3000 rpm in 6th gear. My old T-Bird loafs
>along at 1750. Both have roughly the same hp. My 300 hp V-8 Corvette,
>with a 308 rear end turned about 2750 in 4th if I remember right.
>Anyone know a good source for the relationship between rpm, highway
>speed, horse power, number of gear speeds, etc. How can that old Ford
>engine cruise along at 1750 when it takes the MX-5 3000 rpm? Why do I
>need 6 gears in the Mazda when 4 worked fine in the Corvette? I
>probably knew all these answers 40 years ago, but I need a refresher.


  #5  
Old April 21st 06, 04:20 AM posted to rec.autos.makers.mazda.miata
external usenet poster
 
Posts: n/a
Default rpm vs. speed question

Agreed, 6th is a cruising gear. It shouldn't need high revs. If you need
to be accelerating hard in overdrive, you need to rethink your driving
habits and learn to downshift. That was one of my few major complaints
about my '01.

Eric Lucas

"Chris D'Agnolo" > wrote in message
...
> All good points but I agree with Dave, 6th should be a taller / more
> relaxed cruising gear. I think the car has plenty of power / torque to
> pull a somewhat taller top gear and it would be a big improvement in
> highspeed cruising comfort and in real world highway gas mileage. Both of
> which the miata realistically falls down a bit on.
>
> Chris
> 99BBB
>
> "M. Cantera" > wrote in message
> ...
>> The key de terming factor in the gearing of an engine is the torque
>> the engine produces.
>>
>> Push rod V 8 engines are designed to produce high torque, partly
>> because the push rod design limits the design to 2 valve per cylinder.
>> This design, while economical, limits the rpm that the engine can
>> turn. They usually red line at relatively low rpm (5000 to 6000 rpm)
>>
>> Modern fours, using overhead cams can uses three or four lighter
>> valves with better modern spring, can turn 7000 or 8000 rmp. But
>> since the are smaller displacement they produce much lower torque.
>>
>> The formula for horsepower is:
>>
>> Horsepower = torque * revs/minute * minute/60 seconds * 2*pi * 1/550
>> Horsepower = torque * revs/minute * 1/5252
>>
>> In a very simple way:
>>
>> Suppose your car requires 100 hp to move along at 90 mph.
>>
>> A v-8 rated at 300 ft-lb at 2000 rpm will be producing 114. An
>> engineer will pick the gearing and rear end to produce the right rpm
>> at the wheels.
>>
>> A smaller 4 cylinder engine, producing 140 ft-lbs or torque would have
>> to turn nearly 4300 rpm to produce the power necessary to move the
>> same car at the same 90 mph.
>>
>> As for the gears, the turbo engine puts out 28 % more power than the
>> normal engine, but the full turbo pressure does not kick in until 4500
>> rpm. the red line is at 6500, so the maximum power band fairly
>> narrow. If your gears are too wide, you can fall off the power band
>> when you up shift, so having more gears allow you to keep the engine
>> turning at high rpm while you accelerate. (its also more fun)
>>
>>
>>
>> On 20 Apr 2006 06:13:29 -0700, "laocmo" > wrote:
>>
>>>I've recently acquired a 05 MazdaSpeed Turbo, 6-speed, a retirement
>>>gift for myself. Love it so far. It's been 40 years since as a single
>>>guy I drove a '64 Vette 4-speed. My driver for the last 13 years has
>>>been a 6-cyl '93 T-Bird auto transmission. Now the questions. At 60mph
>>>my Mazda is turning exactly 3000 rpm in 6th gear. My old T-Bird loafs
>>>along at 1750. Both have roughly the same hp. My 300 hp V-8 Corvette,
>>>with a 308 rear end turned about 2750 in 4th if I remember right.
>>>Anyone know a good source for the relationship between rpm, highway
>>>speed, horse power, number of gear speeds, etc. How can that old Ford
>>>engine cruise along at 1750 when it takes the MX-5 3000 rpm? Why do I
>>>need 6 gears in the Mazda when 4 worked fine in the Corvette? I
>>>probably knew all these answers 40 years ago, but I need a refresher.

>>

>
>



  #6  
Old April 21st 06, 06:08 AM posted to rec.autos.makers.mazda.miata
external usenet poster
 
Posts: n/a
Default rpm vs. speed question

The trouble is -- the market! Flat country = lower RPM needed. (Australia)
US- not so flat- higher RPM.
A stiffer 5th or 6th gear also causes a higher torque load, and higher
combustion chamber temperature.
(Not the favorate of warrenty sellers)
> wrote in message
...
> Agreed, 6th is a cruising gear. It shouldn't need high revs. If you need
> to be accelerating hard in overdrive, you need to rethink your driving
> habits and learn to downshift. That was one of my few major complaints
> about my '01.
>
> Eric Lucas
>
> "Chris D'Agnolo" > wrote in message
> ...
> > All good points but I agree with Dave, 6th should be a taller / more
> > relaxed cruising gear. I think the car has plenty of power / torque to
> > pull a somewhat taller top gear and it would be a big improvement in
> > highspeed cruising comfort and in real world highway gas mileage. Both

of
> > which the miata realistically falls down a bit on.
> >
> > Chris
> > 99BBB
> >
> > "M. Cantera" > wrote in message
> > ...
> >> The key de terming factor in the gearing of an engine is the torque
> >> the engine produces.
> >>
> >> Push rod V 8 engines are designed to produce high torque, partly
> >> because the push rod design limits the design to 2 valve per cylinder.
> >> This design, while economical, limits the rpm that the engine can
> >> turn. They usually red line at relatively low rpm (5000 to 6000 rpm)
> >>
> >> Modern fours, using overhead cams can uses three or four lighter
> >> valves with better modern spring, can turn 7000 or 8000 rmp. But
> >> since the are smaller displacement they produce much lower torque.
> >>
> >> The formula for horsepower is:
> >>
> >> Horsepower = torque * revs/minute * minute/60 seconds * 2*pi * 1/550
> >> Horsepower = torque * revs/minute * 1/5252
> >>
> >> In a very simple way:
> >>
> >> Suppose your car requires 100 hp to move along at 90 mph.
> >>
> >> A v-8 rated at 300 ft-lb at 2000 rpm will be producing 114. An
> >> engineer will pick the gearing and rear end to produce the right rpm
> >> at the wheels.
> >>
> >> A smaller 4 cylinder engine, producing 140 ft-lbs or torque would have
> >> to turn nearly 4300 rpm to produce the power necessary to move the
> >> same car at the same 90 mph.
> >>
> >> As for the gears, the turbo engine puts out 28 % more power than the
> >> normal engine, but the full turbo pressure does not kick in until 4500
> >> rpm. the red line is at 6500, so the maximum power band fairly
> >> narrow. If your gears are too wide, you can fall off the power band
> >> when you up shift, so having more gears allow you to keep the engine
> >> turning at high rpm while you accelerate. (its also more fun)
> >>
> >>
> >>
> >> On 20 Apr 2006 06:13:29 -0700, "laocmo" > wrote:
> >>
> >>>I've recently acquired a 05 MazdaSpeed Turbo, 6-speed, a retirement
> >>>gift for myself. Love it so far. It's been 40 years since as a single
> >>>guy I drove a '64 Vette 4-speed. My driver for the last 13 years has
> >>>been a 6-cyl '93 T-Bird auto transmission. Now the questions. At 60mph
> >>>my Mazda is turning exactly 3000 rpm in 6th gear. My old T-Bird loafs
> >>>along at 1750. Both have roughly the same hp. My 300 hp V-8 Corvette,
> >>>with a 308 rear end turned about 2750 in 4th if I remember right.
> >>>Anyone know a good source for the relationship between rpm, highway
> >>>speed, horse power, number of gear speeds, etc. How can that old Ford
> >>>engine cruise along at 1750 when it takes the MX-5 3000 rpm? Why do I
> >>>need 6 gears in the Mazda when 4 worked fine in the Corvette? I
> >>>probably knew all these answers 40 years ago, but I need a refresher.
> >>

> >
> >

>
>



  #7  
Old April 22nd 06, 02:25 AM posted to rec.autos.makers.mazda.miata
external usenet poster
 
Posts: n/a
Default rpm vs. speed question

6th is not a cruising gear in the Mazdaspeed Miata.

The car redlines in 5th at 107 and 6500 rpm, and 6th, while an
overdrive, gets you to 127. The torque on the vehicle is ok on the
lower end, but the fun does not start until 4000 rpm (See
http://www.flyinmiata.com/tech/dyno.asp under 2006 MX-5 versus 2004
Mazdaspeed for the graph)

To get more torque at the low end, you need more displacement, and a
differently geared transmission. For example, the Pontiac Solstice
has a 2.3 liter engine that is rated at 26 more ft-lbs than the NC
mill. That car hits its published 120 mph top speed at 6200 rpm in
4th gear. 5th would reach that same 120 top speed at a lower rpm, so
it is a true "cruising" gear

On Fri, 21 Apr 2006 01:08:10 -0400, "Chuck" >
wrote:

>The trouble is -- the market! Flat country = lower RPM needed. (Australia)
>US- not so flat- higher RPM.
> A stiffer 5th or 6th gear also causes a higher torque load, and higher
>combustion chamber temperature.
>(Not the favorate of warrenty sellers)
> wrote in message
m...
>> Agreed, 6th is a cruising gear. It shouldn't need high revs. If you need
>> to be accelerating hard in overdrive, you need to rethink your driving
>> habits and learn to downshift. That was one of my few major complaints
>> about my '01.


>> >>
>> >> Horsepower = torque * revs/minute * minute/60 seconds * 2*pi * 1/550
>> >> Horsepower = torque * revs/minute * 1/5252
>> >>
>> >> In a very simple way:
>> >>
>> >> Suppose your car requires 100 hp to move along at 90 mph.
>> >>
>> >> A v-8 rated at 300 ft-lb at 2000 rpm will be producing 114. An
>> >> engineer will pick the gearing and rear end to produce the right rpm
>> >> at the wheels.
>> >>
>> >> A smaller 4 cylinder engine, producing 140 ft-lbs or torque would have
>> >> to turn nearly 4300 rpm to produce the power necessary to move the
>> >> same car at the same 90 mph.
>> >>


>>
>>

>


  #8  
Old April 22nd 06, 11:08 PM posted to rec.autos.makers.mazda.miata
external usenet poster
 
Posts: n/a
Default rpm vs. speed question

M. Cantera > wrote:

>6th is not a cruising gear in the Mazdaspeed Miata.


In none of the Miatas. Which is just a waste since the highest gears are
useless anyway from a performance standpoint in a Miata.

Leon, occasionally succeeding not to back out in sixth.
--
Leon van Dommelen Bess, the Miata Bozo, the Miata
http://www.dommelen.net/miata
The only thing better than a white Miata is two white Miatas
  #10  
Old April 23rd 06, 02:06 AM posted to rec.autos.makers.mazda.miata
external usenet poster
 
Posts: n/a
Default rpm vs. speed question

If I remember correctly when doing my research on the 2006 models, the AT, 5
speed, and 6 speed had final drive ratios of .58, .81, .83 respectively.
This would leave the 6 speed running at higher rpms at cruising speed than
the other two. In a small engine, if one does a lot of cruising, lower rpms
are generally better for both engine life an fuel economy. When I bought my
2001 recently, I really wanted the AT, but couldn't locate one in decent
shape because so few of them are available up here. I ended up with the 6
speed because I wanted a LS, and so far have regretted it. Coupled with the
clutch shudder that the previous owner never fixed under warranty, and the
high cruising RPM which really surprized me, I thing I would have been
better off with a 5 speed or the AT. I feel the 6 speed should have been
marketed as a "Performance Option" coupled with the performance suspension,
rather than the only manual transmission in the more expensive models. I
just find the 6 spd lessens my driving experience overall. If I could get a
free swap for either of the other transmissions, I would jump at the
opportunity.

Boreal
2001 LS Silver/tan

"Chris D'Agnolo" > wrote in message
...
> What are you saying, that you never cruise? You're always accelerating?
> You cruise in some other gear than 6th?
>
> My point is, if you're running it up thru the gears (in the real world),
> you've usually finished impressing yourself or your friend at the 107mph
> point but, you know........... is that redlined in 6th or hitting the (top
> speed) wall prior to redline? Maybe they should scoot 5th and 6th up a bit
> and increase top speed to 135 or so, hmmmmm.
>
> Chris
> 99BBB
>
> "M. Cantera" > wrote in message
> ...
>> 6th is not a cruising gear in the Mazdaspeed Miata.
>>
>> The car redlines in 5th at 107 and 6500 rpm, and 6th, while an
>> overdrive, gets you to 127. The torque on the vehicle is ok on the
>> lower end, but the fun does not start until 4000 rpm (See
>> http://www.flyinmiata.com/tech/dyno.asp under 2006 MX-5 versus 2004
>> Mazdaspeed for the graph)
>>
>> To get more torque at the low end, you need more displacement, and a
>> differently geared transmission. For example, the Pontiac Solstice
>> has a 2.3 liter engine that is rated at 26 more ft-lbs than the NC
>> mill. That car hits its published 120 mph top speed at 6200 rpm in
>> 4th gear. 5th would reach that same 120 top speed at a lower rpm, so
>> it is a true "cruising" gear
>>
>> On Fri, 21 Apr 2006 01:08:10 -0400, "Chuck" >
>> wrote:
>>
>>>The trouble is -- the market! Flat country = lower RPM needed.
>>>(Australia)
>>>US- not so flat- higher RPM.
>>> A stiffer 5th or 6th gear also causes a higher torque load, and higher
>>>combustion chamber temperature.
>>>(Not the favorate of warrenty sellers)
> wrote in message
. com...
>>>> Agreed, 6th is a cruising gear. It shouldn't need high revs. If you
>>>> need
>>>> to be accelerating hard in overdrive, you need to rethink your driving
>>>> habits and learn to downshift. That was one of my few major complaints
>>>> about my '01.

>>
>>>> >>
>>>> >> Horsepower = torque * revs/minute * minute/60 seconds * 2*pi * 1/550
>>>> >> Horsepower = torque * revs/minute * 1/5252
>>>> >>
>>>> >> In a very simple way:
>>>> >>
>>>> >> Suppose your car requires 100 hp to move along at 90 mph.
>>>> >>
>>>> >> A v-8 rated at 300 ft-lb at 2000 rpm will be producing 114. An
>>>> >> engineer will pick the gearing and rear end to produce the right rpm
>>>> >> at the wheels.
>>>> >>
>>>> >> A smaller 4 cylinder engine, producing 140 ft-lbs or torque would
>>>> >> have
>>>> >> to turn nearly 4300 rpm to produce the power necessary to move the
>>>> >> same car at the same 90 mph.
>>>> >>

>>
>>>>
>>>>
>>>

>>

>
>



 




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