If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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. >>>> >> >> >>>> >>>> >>> >> > > |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
LIDAR Trial this Week | [email protected] | Driving | 17 | April 9th 06 02:44 AM |
Conflict of Interest | Dave Head | Driving | 154 | November 29th 05 07:47 AM |
Texas speed limit history | John F. Carr | Driving | 7 | November 6th 05 08:29 PM |
IN senate backs bill to raise speed limit to 70 mph | 223rem | Driving | 56 | February 22nd 05 04:21 PM |
Where to get Official Speed Limit Info | [email protected] | Driving | 40 | January 3rd 05 07:10 AM |