View Full Version : the meaningless of revolutions per minute
clyde
05-20-2005, 01:37 PM
To bring back an old discussion, I was walking down a hall today with a child a few steps behind me. I could hear his footsteps quite clearly. While we were traveling at the same speed, he was taking about two steps for every one of mine.
I still don't understand what it matters if an engine revs to an arbitrary but astronomically high number if each revolution is only doing a fraction of the work of a different engine.
Roadstergal
05-20-2005, 01:39 PM
I skip.
rumatt
05-20-2005, 01:42 PM
Agreed.
Torque at high RPM matters. That's exactly what HP measures.
Conclusion: Horsepower is relevant.
EDIT: It's interesting that working with dwarfs made you think of this subject.
To bring back an old discussion, I was walking down a hall today with a child a few steps behind me. I could hear his footsteps quite clearly. While we were traveling at the same speed, he was taking about two steps for every one of mine.
I still don't understand what it matters if an engine revs to an arbitrary but astronomically high number if each revolution is only doing a fraction of the work of a different engine.
It doesn't, as long as a) you gear the car correctly, and b) the torque curve is flat enough that you aren't stuck with a huge surge at the end of the rev range and nothing underneath.
(B) is why I'd consider buying an RX-8 and would never consider buying an S2000, despite the overt similarities of their various peak numbers. But it's a problem that isn't entirely related to having a high redline--there could be a peaky engine with a low redline, too.
It's also why MHz is irrelevant when comparing CPUs of different architectures. (PowerPC vs. x386)
Roadstergal
05-20-2005, 01:59 PM
But even at the same speed, the kid behind clyde might be more fun.
It's a personal preference, but as long as you both get to the same place...
John V
05-20-2005, 02:28 PM
But even at the same speed, the kid behind clyde might be more fun.
I can't imagine anyone being more fun than clyde.
:mad:
rumatt
05-20-2005, 03:13 PM
It's also why MHz is irrelevant when comparing CPUs of different architectures. (PowerPC vs. x386)
MHz is irrelevant because Clyde has long legs and/or works with midgets? Cool.
:P
Pinecone
05-20-2005, 03:41 PM
Torque matters.
The common water wheel will still acelerate a car like stink if properly geared, it is just that you will gear UP to generate RPM at the wheels.
rumatt
05-20-2005, 04:00 PM
Torque matters.
I actually disagree. Torque and RPM must be considered together. Infinitely large torque at infinitely small RPM gives you nothing.
Increasing either one more than you reduce the other is a good thing.
Roadstergal
05-20-2005, 04:02 PM
Still - isn't that like saying speed is irrelevant, as long as you get where you're going? Getting there faster than some arbitraty number is just personal preference. And if you're on a track, you always end up where you start.
I think torque is convenient, to a point, but high RPM is fun. And that's my preference.
rumatt
05-20-2005, 04:03 PM
And if you're on a track, you always end up where you start.
Plus driving in circles generates torque? Which is important.
:scratch:
Roadstergal
05-20-2005, 04:03 PM
Driving in circles generates torque, right? Isn't that more important than speed?
But does it really matter how fast I go in circles? ;)
It's also why MHz is irrelevant when comparing CPUs of different architectures. (PowerPC vs. x386)
MHz is irrelevant because Clyde has long legs and/or works with midgets? Cool.
:P
Don't forget the masculine hands and the guy having fun behind clyde.
:lol:
Pinecone
05-20-2005, 05:49 PM
Torque matters.
I actually disagree. Torque and RPM must be considered together. Infinitely large torque at infinitely small RPM gives you nothing.
Increasing either one more than you reduce the other is a good thing.
Let's see, if I have something that generates some 30,000 pounds feet of torque at say 30 RPM, if I gear that up to 3000 RPM, I still get 300 pounds feet of torque, or 171 HP. There are limits, but if you have lots of torque you can make RPM. If you have low torque, but have RPM, you can use gears to torque multiply.Say 3,000,000 pounds feet at 3 RPM, gives you 1,000 pounds feet at 1000 RPM or 500 pounds feet at 2000 RPM, still 190 HP.
Best is lots of torque over a wide range to hgh RPM.
rumatt
05-20-2005, 06:56 PM
There are limits, but if you have lots of torque you can make RPM.
Agreed.
If you have low torque, but have RPM, you can use gears to torque multiply.
Agreed.
Best is lots of torque over a wide range to hgh RPM.
Agreed.
Geez. What did I originally disagree with? I guess it was implication that torque is more important than RPM... which now that I look back, you never said. :scratch:
lemming
05-20-2005, 10:00 PM
To bring back an old discussion, I was walking down a hall today with a child a few steps behind me. I could hear his footsteps quite clearly. While we were traveling at the same speed, he was taking about two steps for every one of mine.
I still don't understand what it matters if an engine revs to an arbitrary but astronomically high number if each revolution is only doing a fraction of the work of a different engine.
you mean sort of like loafing at 80mph at about 2200rpms (approximate)?
:lol:
what BMW has proven is that high revving engines are best left to either ferrari (50,000 USD per engine) or to the japanese. :-D --their forte are midrange motors that breathe well throughout the more normal powerband.
I skip.
You need a tune up?
The V runs at about 2200 rpms at 80 mph. Doesn't have much torque in that gear though. At least comparatively. It won' slam you head back against the head rest and scream in ecstasy unless you put it in third at that speed. The rpms at 80 in third are . . . a lot higher. :)
lemming
05-24-2005, 08:32 PM
wait a minute.
Snyde is disparaging high revving engines?
JetBlack330i
05-25-2005, 10:21 AM
Geez. What did I originally disagree with? I guess it was implication that torque is more important than RPM... which now that I look back, you never said. :scratch:Disagree.
Both, torque and rpm are important, and that is precisely why engines specs list both.
I'm speculating that Clyde's original context is in F1. Like why does it matter to know that an F1 engine runs at 18K rpm (as opposed to the more mundane ranges in production cars)? People cite those numbers as an indicator of technical superiority. It is not trivial to make a piston travel that fast while taking the abuses an F1 race imposes.
In production cars, the tachometer is there to show not the absolute number, but the relative position in the range, so the driver can position the needle in the optimal range for the situation.
Roadstergal
05-25-2005, 12:01 PM
Oh, if we're talking F1, it's the sheer aural, sensual delight of listening to those V-10s scream. Which goes along with what I'm saying - I would not fly to Indy and pay to listen to some engines burble along at 2200rpm, even if they were faster.
rumatt
05-25-2005, 12:21 PM
I would not fly to Indy and pay to listen to some engines burble along at 2200rpm, even if they were faster.
Wow, I never took you to be the show-over-go type.
Kinda like bling bling, but different.
Kinda like bling bling, but different.
:lol:
John V
05-25-2005, 12:27 PM
Oh, if we're talking F1, it's the sheer aural, sensual delight of listening to those V-10s scream. Which goes along with what I'm saying - I would not fly to Indy and pay to listen to some engines burble along at 2200rpm, even if they were faster.
The technology is great.
The cars are neat.
The tracks are awesome.
The racing sucks. :yawn:
The technology is great.
The cars are neat.
The tracks are awesome.
The racing sucks. :yawn:
Only because the same guy walks away and wins almost every race.
The technology is great.
The cars are neat.
The tracks are awesome.
The racing sucks. :yawn:
Only because the same guy walks away and wins almost every race.
When was the last time you guys watched F1? Ferrari's been rather underwhelming this year, to put it mildly.
clyde
05-25-2005, 01:01 PM
If they ain't rubbing, they ain't racing.
Seriously, it's a technological tour de force that appeals to the geek gearhead in me, but it's a complete bore to watch. Even if Ferarri is underwhelming, it's still just a contest of the best car-driver combo with the definition of "best" including least likely to break. They may as well just do Solo I like time trials and let everyone go home early. It's not like the driver or manufacturer standings would change much.
If they ain't rubbing, they ain't racing.
Seriously, it's a technological tour de force that appeals to the geek gearhead in me, but it's a complete bore to watch. Even if Ferarri is underwhelming, it's still just a contest of the best car-driver combo with the definition of "best" including least likely to break. They may as well just do Solo I like time trials and let everyone go home early. It's not like the driver or manufacturer standings would change much.
Rubbing aside, there's plenty of overtaking this season. Even Monaco was exciting to watch as long as you kept the camera off of Kimi. And even without the passing, the machines are just jaw droppingly cool.
Of course, I also believe that a lot of the artificial rules that define engine specs and body specs detract from the engineering competition. I'd rather see a "salary cap" with a loose set of regulations.
John V
05-25-2005, 02:19 PM
Of course, I also believe that a lot of the artificial rules that define engine specs and body specs detract from the engineering competition. I'd rather see a "salary cap" with a loose set of regulations.
I'd rather get rid of 90% of the wings and ground effects to try to improve drafting and passing.
Roadstergal
05-25-2005, 02:46 PM
Kinda like bling bling, but different.
Zoom zoom. :)
Paul, one of the post-docs in the lab, has IMO a very good idea. He wants to see regulations on aero based on wind-tunnel testing of two cars, and designed to minimize the effect of the front car's aero on the car behind. Screwing with aero to cut cornering speeds is IMO stupid; make the corner speeds as high as folk can get, just eliminate the aero penalty for the car behind. That would help passing more than any of the current "changes" will.
When was the last time you guys watched F1? Ferrari's been rather underwhelming this year, to put it mildly.
That would have to be last summer. Having no Speed channel this year has hurt my ability to watch racing on TV. And I don't read the newspaper, watch the news on TV, or even tune into ESPN (not that any of those cater much to anything outside of NASCAR or the Indy500).
Of course, I also believe that a lot of the artificial rules that define engine specs and body specs detract from the engineering competition. I'd rather see a "salary cap" with a loose set of regulations.
That's an outstanding idea. Kind of like, "here's $10, a stick, and a piece of string. Build me the best widget that you can." The only problem would be trying to govern the financials of the race teams, ensuring that nobody spends more than $XX in developing and producing a fleet of racecars.
Of course, I also believe that a lot of the artificial rules that define engine specs and body specs detract from the engineering competition. I'd rather see a "salary cap" with a loose set of regulations.
That's an outstanding idea. Kind of like, "here's $10, a stick, and a piece of string. Build me the best widget that you can." The only problem would be trying to govern the financials of the race teams, ensuring that nobody spends more than $XX in developing and producing a fleet of racecars.
Yeah, I agree. I don't know if it's reasonably possible to enforce a spending limit in F1. Unfortunately, not having spending limits will result in the situation we have now, where dominance is at least partially correlated to budget. I don't see Jordan winning any time soon, ever, largely because they can't afford the same design, testing, driving, and building as Ferrari/BMW/MB. The problem is that spending wars can only escalate, which really just mucks it up for everbody -- including the winners.
I really like the idea of returning F1 to nearly unrestricted design, from engine specs to chassis dimensions. A spending cap would force all competitors to get creative and innovate without spending each other into the ground. But I don't know how anyone could get around things like paying engineers a "salary" of $1, or other bookkeeping tricks, never mind enforcing the spending limit in a more general sense.
Roadstergal
05-25-2005, 04:37 PM
A spending limit would never work. Spending sets an entry level, FWIW; it doesn't guarantee a win. In my mind, you'll get more bang for your buck (so to speak) out of enforceable design-type restrictions.
A spending limit would never work. Spending sets an entry level, FWIW; it doesn't guarantee a win. In my mind, you'll get more bang for your buck (so to speak) out of enforceable design-type restrictions.
Design rules work to a point. The big spender teams in F1 are all legitimately in the thick of the championship, but the smaller teams don't have a prayer and they never will. What's more, I read about F1 racing from a generation or so ago and I wonder what happened to all of the engine variety, chassis variety, and everything else that the teams once could modify to suit their individual strategies. Some people argue that the restrictions were put into place because too much money was being spent on building the best chassis. I'd rather see teams spend a certain amount and come up with the best designs that work for them -- turbocharged V8, N/A V10, nitrous-running I4 with sucker ground effects -- whatever works. These days, a walrus-nosed BMW is about as close as it gets to a revolution...and it didn't even work.
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