Altima SE V-6 vs. Accord LX V-6
12-21-2004 | 06:33 PM
#46
Guest
Posts: n/a
Torque vs. horsepower
Found this helpful - http://www.vettenet.org/torquehp.html
Here's my take.
Power rules for acceleration, and a flat power output curve means faster
acceleration. A flat power output curve is suggested by a relatively
high-RPM torque peak.
It takes energy (or power, power being the time rate of energy application)
to accelerate a car. An engine generating more power (in each given instant
of time) will accelerate the car faster (in that instant). Period. Torque
is not the same as work, energy or power. You can indeed stand on a
stationary breaker bar and exceed the torque output of a typical car engine.
But standing on a breaker bar won't move a car 0-60 in 8 seconds or less.
Torque x rotational speed does equal power. (Must throw in conversion
factors when using English units: Power [as hp] = torque [as ft-lbs] x
rotational speed [as RPM] / 5252.)
In practice, if an engine produces peak torque at a relatively lower RPM,
the power curve for that engine is more strongly sloped down from peak
horsepower. It doesn't produce anywhere near the highest horsepower except
at its peak horsepower speed. At practically all speeds in all gears
(except near the peak speed in each gear) the power output is far below the
engine's maximum output. Less power most of the time = Slower acceleration.
But the engine will seem to be more flexible in normal driving, i.e., not
requiring gear shifts all the time.
On the other hand, an engine that produces peak torque at a higher RPM has a
flatter power output curve at the upper RPM's -- the power is more usable --
doesn't require a large number of exact gears to extract max. hp, and it
accelerates faster. But to many drivers, it'll be a pain when strong
accceleration is called for because it more often requires downshifting to
keep the revs up.
--Pete
<dold@XReXXAltim.usenet.us.com> wrote in message
news:cp9osu$13c$1@blue.rahul.net...
> In rec.autos.makers.honda Hawaii_SE-R <WhyUGottaSpam@me.com> wrote:
> > I highly doubt you could produce more torque than the VQ35DE on your
> > bicycle.
>
> More than the Honda anyway. What was that, 214 lb/ft? ( what's a "tq"
?).
> Assuming the pedal on the bicycle is one foot long, which it might not be,
> and that I weigh 214 pounds, all I have to do is stand on the pedal.
> 214 lbs/ft of torque. I could get more by pulling up on the handlebar as
I
> pressed down on the pedal.
> How many horespower is that? If I could pedal the bicycle at that rate
for
> one full second it would be 214/550 = .38 hp.
>
> ---
> Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
>
>
Here's my take.
Power rules for acceleration, and a flat power output curve means faster
acceleration. A flat power output curve is suggested by a relatively
high-RPM torque peak.
It takes energy (or power, power being the time rate of energy application)
to accelerate a car. An engine generating more power (in each given instant
of time) will accelerate the car faster (in that instant). Period. Torque
is not the same as work, energy or power. You can indeed stand on a
stationary breaker bar and exceed the torque output of a typical car engine.
But standing on a breaker bar won't move a car 0-60 in 8 seconds or less.
Torque x rotational speed does equal power. (Must throw in conversion
factors when using English units: Power [as hp] = torque [as ft-lbs] x
rotational speed [as RPM] / 5252.)
In practice, if an engine produces peak torque at a relatively lower RPM,
the power curve for that engine is more strongly sloped down from peak
horsepower. It doesn't produce anywhere near the highest horsepower except
at its peak horsepower speed. At practically all speeds in all gears
(except near the peak speed in each gear) the power output is far below the
engine's maximum output. Less power most of the time = Slower acceleration.
But the engine will seem to be more flexible in normal driving, i.e., not
requiring gear shifts all the time.
On the other hand, an engine that produces peak torque at a higher RPM has a
flatter power output curve at the upper RPM's -- the power is more usable --
doesn't require a large number of exact gears to extract max. hp, and it
accelerates faster. But to many drivers, it'll be a pain when strong
accceleration is called for because it more often requires downshifting to
keep the revs up.
--Pete
<dold@XReXXAltim.usenet.us.com> wrote in message
news:cp9osu$13c$1@blue.rahul.net...
> In rec.autos.makers.honda Hawaii_SE-R <WhyUGottaSpam@me.com> wrote:
> > I highly doubt you could produce more torque than the VQ35DE on your
> > bicycle.
>
> More than the Honda anyway. What was that, 214 lb/ft? ( what's a "tq"
?).
> Assuming the pedal on the bicycle is one foot long, which it might not be,
> and that I weigh 214 pounds, all I have to do is stand on the pedal.
> 214 lbs/ft of torque. I could get more by pulling up on the handlebar as
I
> pressed down on the pedal.
> How many horespower is that? If I could pedal the bicycle at that rate
for
> one full second it would be 214/550 = .38 hp.
>
> ---
> Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
>
>
12-21-2004 | 06:33 PM
#47
Guest
Posts: n/a
Torque vs. horsepower
Found this helpful - http://www.vettenet.org/torquehp.html
Here's my take.
Power rules for acceleration, and a flat power output curve means faster
acceleration. A flat power output curve is suggested by a relatively
high-RPM torque peak.
It takes energy (or power, power being the time rate of energy application)
to accelerate a car. An engine generating more power (in each given instant
of time) will accelerate the car faster (in that instant). Period. Torque
is not the same as work, energy or power. You can indeed stand on a
stationary breaker bar and exceed the torque output of a typical car engine.
But standing on a breaker bar won't move a car 0-60 in 8 seconds or less.
Torque x rotational speed does equal power. (Must throw in conversion
factors when using English units: Power [as hp] = torque [as ft-lbs] x
rotational speed [as RPM] / 5252.)
In practice, if an engine produces peak torque at a relatively lower RPM,
the power curve for that engine is more strongly sloped down from peak
horsepower. It doesn't produce anywhere near the highest horsepower except
at its peak horsepower speed. At practically all speeds in all gears
(except near the peak speed in each gear) the power output is far below the
engine's maximum output. Less power most of the time = Slower acceleration.
But the engine will seem to be more flexible in normal driving, i.e., not
requiring gear shifts all the time.
On the other hand, an engine that produces peak torque at a higher RPM has a
flatter power output curve at the upper RPM's -- the power is more usable --
doesn't require a large number of exact gears to extract max. hp, and it
accelerates faster. But to many drivers, it'll be a pain when strong
accceleration is called for because it more often requires downshifting to
keep the revs up.
--Pete
<dold@XReXXAltim.usenet.us.com> wrote in message
news:cp9osu$13c$1@blue.rahul.net...
> In rec.autos.makers.honda Hawaii_SE-R <WhyUGottaSpam@me.com> wrote:
> > I highly doubt you could produce more torque than the VQ35DE on your
> > bicycle.
>
> More than the Honda anyway. What was that, 214 lb/ft? ( what's a "tq"
?).
> Assuming the pedal on the bicycle is one foot long, which it might not be,
> and that I weigh 214 pounds, all I have to do is stand on the pedal.
> 214 lbs/ft of torque. I could get more by pulling up on the handlebar as
I
> pressed down on the pedal.
> How many horespower is that? If I could pedal the bicycle at that rate
for
> one full second it would be 214/550 = .38 hp.
>
> ---
> Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
>
>
Here's my take.
Power rules for acceleration, and a flat power output curve means faster
acceleration. A flat power output curve is suggested by a relatively
high-RPM torque peak.
It takes energy (or power, power being the time rate of energy application)
to accelerate a car. An engine generating more power (in each given instant
of time) will accelerate the car faster (in that instant). Period. Torque
is not the same as work, energy or power. You can indeed stand on a
stationary breaker bar and exceed the torque output of a typical car engine.
But standing on a breaker bar won't move a car 0-60 in 8 seconds or less.
Torque x rotational speed does equal power. (Must throw in conversion
factors when using English units: Power [as hp] = torque [as ft-lbs] x
rotational speed [as RPM] / 5252.)
In practice, if an engine produces peak torque at a relatively lower RPM,
the power curve for that engine is more strongly sloped down from peak
horsepower. It doesn't produce anywhere near the highest horsepower except
at its peak horsepower speed. At practically all speeds in all gears
(except near the peak speed in each gear) the power output is far below the
engine's maximum output. Less power most of the time = Slower acceleration.
But the engine will seem to be more flexible in normal driving, i.e., not
requiring gear shifts all the time.
On the other hand, an engine that produces peak torque at a higher RPM has a
flatter power output curve at the upper RPM's -- the power is more usable --
doesn't require a large number of exact gears to extract max. hp, and it
accelerates faster. But to many drivers, it'll be a pain when strong
accceleration is called for because it more often requires downshifting to
keep the revs up.
--Pete
<dold@XReXXAltim.usenet.us.com> wrote in message
news:cp9osu$13c$1@blue.rahul.net...
> In rec.autos.makers.honda Hawaii_SE-R <WhyUGottaSpam@me.com> wrote:
> > I highly doubt you could produce more torque than the VQ35DE on your
> > bicycle.
>
> More than the Honda anyway. What was that, 214 lb/ft? ( what's a "tq"
?).
> Assuming the pedal on the bicycle is one foot long, which it might not be,
> and that I weigh 214 pounds, all I have to do is stand on the pedal.
> 214 lbs/ft of torque. I could get more by pulling up on the handlebar as
I
> pressed down on the pedal.
> How many horespower is that? If I could pedal the bicycle at that rate
for
> one full second it would be 214/550 = .38 hp.
>
> ---
> Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
>
>
12-21-2004 | 07:34 PM
#48
Guest
Posts: n/a
Re: Torque vs. horsepower
In article <zp2yd.4204$_X7.3909@newssvr33.news.prodigy.com> , <nospam@none.nul> wrote:
>Found this helpful - http://www.vettenet.org/torquehp.html
Ah, that post has made the rounds for years (not saying it is
right, wrong, or lucid).
>Here's my take.
The physics is fine, but either I'm not following, or disagree
with the following...
>a flat power output curve means faster
>acceleration. A flat power output curve is suggested by a relatively
>high-RPM torque peak.
What do you mean by "flat power curve"? By their nature, IC
engines tend to have flatter torque curves. If you had an "ideal"
flat torque curve (and it really is debatable as to whether this
is ideal), the hp curve would linearly increase with rpm. So the
power curve is decidedly _not_ flat.
As an aside, note some electric motor types approach the flat hp
curve. Their torque curve starts out with a high plateau at low
rpm, then follows a decreasing hyperbola at higher rpm (ie flat,
constant, peak power). But ICE's look nothing like this.
[skipping down ...]
>In practice, if an engine produces peak torque at a relatively lower RPM,
>the power curve for that engine is more strongly sloped down from peak
>horsepower.
Not sure this generality is accurate.
>It doesn't produce anywhere near the highest horsepower except
>at its peak horsepower speed.
That goes for any ICE. Including high-revvers.
>At practically all speeds in all gears
>(except near the peak speed in each gear) the power output is far below the
>engine's maximum output.
Again, that goes for any ICE. Again assuming the flat torque
curve, then power = Constant*rpm. So fraction of peak power =
present rpm / peak hp rpm. Since a high-revver has the peak hp at
a higher rpm, I think it would be more likely than not that you'd
be further away. Which is the same as what you said about having
to downshift to get at the hi-revver's power.
>But the engine will seem to be more flexible in normal driving, i.e., not
>requiring gear shifts all the time.
Agreed. Basically, if you want to drive at low rpm, get the big
displacement engine.
>On the other hand, an engine that produces peak torque at a higher RPM has a
>flatter power output curve at the upper RPM's
Again, I do not see this generality as being obviously true.
Sorry.
Give me two engines with the same hp, but widely different torque
ratings in otherwise identical vehicles (choose gearing to best
suit each) and they'll have just about the same best accel
numbers. But in "normal" driving, most will perceive (scratch
that, actually get) better accel in the big displacement, high
torque engine since most will not normally be at the hi revs where
the hi-revver makes up ground.
Your physics still holds. In *most* "normal" situations, the
big-torque engine will be making more hp than the hi-revver.
Unless you consider normal driving to be above 6000 rpm.
>Found this helpful - http://www.vettenet.org/torquehp.html
Ah, that post has made the rounds for years (not saying it is
right, wrong, or lucid).
>Here's my take.
The physics is fine, but either I'm not following, or disagree
with the following...
>a flat power output curve means faster
>acceleration. A flat power output curve is suggested by a relatively
>high-RPM torque peak.
What do you mean by "flat power curve"? By their nature, IC
engines tend to have flatter torque curves. If you had an "ideal"
flat torque curve (and it really is debatable as to whether this
is ideal), the hp curve would linearly increase with rpm. So the
power curve is decidedly _not_ flat.
As an aside, note some electric motor types approach the flat hp
curve. Their torque curve starts out with a high plateau at low
rpm, then follows a decreasing hyperbola at higher rpm (ie flat,
constant, peak power). But ICE's look nothing like this.
[skipping down ...]
>In practice, if an engine produces peak torque at a relatively lower RPM,
>the power curve for that engine is more strongly sloped down from peak
>horsepower.
Not sure this generality is accurate.
>It doesn't produce anywhere near the highest horsepower except
>at its peak horsepower speed.
That goes for any ICE. Including high-revvers.
>At practically all speeds in all gears
>(except near the peak speed in each gear) the power output is far below the
>engine's maximum output.
Again, that goes for any ICE. Again assuming the flat torque
curve, then power = Constant*rpm. So fraction of peak power =
present rpm / peak hp rpm. Since a high-revver has the peak hp at
a higher rpm, I think it would be more likely than not that you'd
be further away. Which is the same as what you said about having
to downshift to get at the hi-revver's power.
>But the engine will seem to be more flexible in normal driving, i.e., not
>requiring gear shifts all the time.
Agreed. Basically, if you want to drive at low rpm, get the big
displacement engine.
>On the other hand, an engine that produces peak torque at a higher RPM has a
>flatter power output curve at the upper RPM's
Again, I do not see this generality as being obviously true.
Sorry.
Give me two engines with the same hp, but widely different torque
ratings in otherwise identical vehicles (choose gearing to best
suit each) and they'll have just about the same best accel
numbers. But in "normal" driving, most will perceive (scratch
that, actually get) better accel in the big displacement, high
torque engine since most will not normally be at the hi revs where
the hi-revver makes up ground.
Your physics still holds. In *most* "normal" situations, the
big-torque engine will be making more hp than the hi-revver.
Unless you consider normal driving to be above 6000 rpm.
12-21-2004 | 07:34 PM
#49
Guest
Posts: n/a
Re: Torque vs. horsepower
In article <zp2yd.4204$_X7.3909@newssvr33.news.prodigy.com> , <nospam@none.nul> wrote:
>Found this helpful - http://www.vettenet.org/torquehp.html
Ah, that post has made the rounds for years (not saying it is
right, wrong, or lucid).
>Here's my take.
The physics is fine, but either I'm not following, or disagree
with the following...
>a flat power output curve means faster
>acceleration. A flat power output curve is suggested by a relatively
>high-RPM torque peak.
What do you mean by "flat power curve"? By their nature, IC
engines tend to have flatter torque curves. If you had an "ideal"
flat torque curve (and it really is debatable as to whether this
is ideal), the hp curve would linearly increase with rpm. So the
power curve is decidedly _not_ flat.
As an aside, note some electric motor types approach the flat hp
curve. Their torque curve starts out with a high plateau at low
rpm, then follows a decreasing hyperbola at higher rpm (ie flat,
constant, peak power). But ICE's look nothing like this.
[skipping down ...]
>In practice, if an engine produces peak torque at a relatively lower RPM,
>the power curve for that engine is more strongly sloped down from peak
>horsepower.
Not sure this generality is accurate.
>It doesn't produce anywhere near the highest horsepower except
>at its peak horsepower speed.
That goes for any ICE. Including high-revvers.
>At practically all speeds in all gears
>(except near the peak speed in each gear) the power output is far below the
>engine's maximum output.
Again, that goes for any ICE. Again assuming the flat torque
curve, then power = Constant*rpm. So fraction of peak power =
present rpm / peak hp rpm. Since a high-revver has the peak hp at
a higher rpm, I think it would be more likely than not that you'd
be further away. Which is the same as what you said about having
to downshift to get at the hi-revver's power.
>But the engine will seem to be more flexible in normal driving, i.e., not
>requiring gear shifts all the time.
Agreed. Basically, if you want to drive at low rpm, get the big
displacement engine.
>On the other hand, an engine that produces peak torque at a higher RPM has a
>flatter power output curve at the upper RPM's
Again, I do not see this generality as being obviously true.
Sorry.
Give me two engines with the same hp, but widely different torque
ratings in otherwise identical vehicles (choose gearing to best
suit each) and they'll have just about the same best accel
numbers. But in "normal" driving, most will perceive (scratch
that, actually get) better accel in the big displacement, high
torque engine since most will not normally be at the hi revs where
the hi-revver makes up ground.
Your physics still holds. In *most* "normal" situations, the
big-torque engine will be making more hp than the hi-revver.
Unless you consider normal driving to be above 6000 rpm.
>Found this helpful - http://www.vettenet.org/torquehp.html
Ah, that post has made the rounds for years (not saying it is
right, wrong, or lucid).
>Here's my take.
The physics is fine, but either I'm not following, or disagree
with the following...
>a flat power output curve means faster
>acceleration. A flat power output curve is suggested by a relatively
>high-RPM torque peak.
What do you mean by "flat power curve"? By their nature, IC
engines tend to have flatter torque curves. If you had an "ideal"
flat torque curve (and it really is debatable as to whether this
is ideal), the hp curve would linearly increase with rpm. So the
power curve is decidedly _not_ flat.
As an aside, note some electric motor types approach the flat hp
curve. Their torque curve starts out with a high plateau at low
rpm, then follows a decreasing hyperbola at higher rpm (ie flat,
constant, peak power). But ICE's look nothing like this.
[skipping down ...]
>In practice, if an engine produces peak torque at a relatively lower RPM,
>the power curve for that engine is more strongly sloped down from peak
>horsepower.
Not sure this generality is accurate.
>It doesn't produce anywhere near the highest horsepower except
>at its peak horsepower speed.
That goes for any ICE. Including high-revvers.
>At practically all speeds in all gears
>(except near the peak speed in each gear) the power output is far below the
>engine's maximum output.
Again, that goes for any ICE. Again assuming the flat torque
curve, then power = Constant*rpm. So fraction of peak power =
present rpm / peak hp rpm. Since a high-revver has the peak hp at
a higher rpm, I think it would be more likely than not that you'd
be further away. Which is the same as what you said about having
to downshift to get at the hi-revver's power.
>But the engine will seem to be more flexible in normal driving, i.e., not
>requiring gear shifts all the time.
Agreed. Basically, if you want to drive at low rpm, get the big
displacement engine.
>On the other hand, an engine that produces peak torque at a higher RPM has a
>flatter power output curve at the upper RPM's
Again, I do not see this generality as being obviously true.
Sorry.
Give me two engines with the same hp, but widely different torque
ratings in otherwise identical vehicles (choose gearing to best
suit each) and they'll have just about the same best accel
numbers. But in "normal" driving, most will perceive (scratch
that, actually get) better accel in the big displacement, high
torque engine since most will not normally be at the hi revs where
the hi-revver makes up ground.
Your physics still holds. In *most* "normal" situations, the
big-torque engine will be making more hp than the hi-revver.
Unless you consider normal driving to be above 6000 rpm.
12-22-2004 | 06:53 AM
#50
Guest
Posts: n/a
Re: Torque vs. horsepower
"Dave" <dm@nospam.com> wrote in message
news:Ri3yd.40734$DQ3.40664@twister.nyroc.rr.com...
> In article <zp2yd.4204$_X7.3909@newssvr33.news.prodigy.com> ,
<nospam@none.nul> wrote:
> >Found this helpful - http://www.vettenet.org/torquehp.html
>
> Ah, that post has made the rounds for years (not saying it is
> right, wrong, or lucid).
>
> >Here's my take.
>
> The physics is fine, but either I'm not following, or disagree
> with the following...
>
> >a flat power output curve means faster
> >acceleration. A flat power output curve is suggested by a relatively
> >high-RPM torque peak.
>
> What do you mean by "flat power curve"? By their nature, IC
> engines tend to have flatter torque curves. If you had an "ideal"
> flat torque curve (and it really is debatable as to whether this
> is ideal), the hp curve would linearly increase with rpm. So the
> power curve is decidedly _not_ flat.
No, I meant a flat power curve. That implies a torque curve that decreases
linearly with RPM.
>
> As an aside, note some electric motor types approach the flat hp
> curve. Their torque curve starts out with a high plateau at low
> rpm, then follows a decreasing hyperbola at higher rpm (ie flat,
> constant, peak power). But ICE's look nothing like this.
>
> [skipping down ...]
>
> >In practice, if an engine produces peak torque at a relatively lower RPM,
> >the power curve for that engine is more strongly sloped down from peak
> >horsepower.
>
> Not sure this generality is accurate.
OK.... See reply below.
>
> >It doesn't produce anywhere near the highest horsepower except
> >at its peak horsepower speed.
>
> That goes for any ICE. Including high-revvers.
>
> >At practically all speeds in all gears
> >(except near the peak speed in each gear) the power output is far below
the
> >engine's maximum output.
>
> Again, that goes for any ICE. Again assuming the flat torque
> curve, then power = Constant*rpm. So fraction of peak power =
> present rpm / peak hp rpm. Since a high-revver has the peak hp at
> a higher rpm, I think it would be more likely than not that you'd
> be further away. Which is the same as what you said about having
> to downshift to get at the hi-revver's power.
>
>
> >But the engine will seem to be more flexible in normal driving, i.e., not
> >requiring gear shifts all the time.
>
> Agreed. Basically, if you want to drive at low rpm, get the big
> displacement engine.
>
> >On the other hand, an engine that produces peak torque at a higher RPM
has a
> >flatter power output curve at the upper RPM's
>
> Again, I do not see this generality as being obviously true.
> Sorry.
>
> Give me two engines with the same hp, but widely different torque
> ratings in otherwise identical vehicles (choose gearing to best
> suit each) and they'll have just about the same best accel
> numbers. But in "normal" driving, most will perceive (scratch
> that, actually get) better accel in the big displacement, high
> torque engine since most will not normally be at the hi revs where
> the hi-revver makes up ground.
>
> Your physics still holds. In *most* "normal" situations, the
> big-torque engine will be making more hp than the hi-revver.
> Unless you consider normal driving to be above 6000 rpm.
My main purpose was to state some laws of physics, to clear up some false,
garbled, or (at best) incomplete statements in earlier posts (Accord vs.
Altima thread).
OK, I went out on a limb writing about car engines. You caught me. Went
looking for evidence... took engine hp & torque ratings from Car & Driver
auto reviews, and made the following table. (If the table is unreadable, set
your newsreader font to Courier and maximize the window...)
Table: Horsepower at Max. Torque for Several Auto Engines
HP, Torque (mfr rating)@ Eng Spd HP @ Max Torque %HP at %RPM
(@Max Torque)
altima v-6
240 bhp @ 5800 rpm 86% of peak
hp at
246 ft-lb @ 4400 rpm 206 hp 76% of
max.HP rpm
pontiac g6 gt
200 bhp @ 5400 rpm 80% of peak
hp at
220 ft-lb @ 3800 rpm 159 hp 70% of
max.HP rpm
accord v-6
240 bhp @ 6250 rpm 84% of peak
hp at
212 ft-lb @ 5000 rpm 202 hp 80% of
max.HP rpm
cherokee v-8
235 bhp @ 4800 rpm 76% of peak
hp at
295 ft-lb @ 3200 rpm 180 hp 67% of
max.HP rpm
scion tc
160 bhp @ 5700 rpm 78% of peak
hp at
163 ft-lb @ 4000 rpm 124 hp 70% of
max.HP rpm
It looks like the engines that make max. torque at lower %RPM make a
relatively higher %HP at that RPM, so this supports your view (I guess...
it's a small sample and there are lots of details ignored...). ***You're
saying that if two engines have identical peak HP @ x-RPM, the one that has
peak torque at lower RPM will (generally) have better usable power output --
give better acceleraction?*** In other words, does this lower peak torque
mean the engine was engineered 'better' for acceleration, given a typical
drivetrain (limited # of gears, no hybrid help) .
Thanks for your input.
---
12-22-2004 | 06:53 AM
#51
Guest
Posts: n/a
Re: Torque vs. horsepower
"Dave" <dm@nospam.com> wrote in message
news:Ri3yd.40734$DQ3.40664@twister.nyroc.rr.com...
> In article <zp2yd.4204$_X7.3909@newssvr33.news.prodigy.com> ,
<nospam@none.nul> wrote:
> >Found this helpful - http://www.vettenet.org/torquehp.html
>
> Ah, that post has made the rounds for years (not saying it is
> right, wrong, or lucid).
>
> >Here's my take.
>
> The physics is fine, but either I'm not following, or disagree
> with the following...
>
> >a flat power output curve means faster
> >acceleration. A flat power output curve is suggested by a relatively
> >high-RPM torque peak.
>
> What do you mean by "flat power curve"? By their nature, IC
> engines tend to have flatter torque curves. If you had an "ideal"
> flat torque curve (and it really is debatable as to whether this
> is ideal), the hp curve would linearly increase with rpm. So the
> power curve is decidedly _not_ flat.
No, I meant a flat power curve. That implies a torque curve that decreases
linearly with RPM.
>
> As an aside, note some electric motor types approach the flat hp
> curve. Their torque curve starts out with a high plateau at low
> rpm, then follows a decreasing hyperbola at higher rpm (ie flat,
> constant, peak power). But ICE's look nothing like this.
>
> [skipping down ...]
>
> >In practice, if an engine produces peak torque at a relatively lower RPM,
> >the power curve for that engine is more strongly sloped down from peak
> >horsepower.
>
> Not sure this generality is accurate.
OK.... See reply below.
>
> >It doesn't produce anywhere near the highest horsepower except
> >at its peak horsepower speed.
>
> That goes for any ICE. Including high-revvers.
>
> >At practically all speeds in all gears
> >(except near the peak speed in each gear) the power output is far below
the
> >engine's maximum output.
>
> Again, that goes for any ICE. Again assuming the flat torque
> curve, then power = Constant*rpm. So fraction of peak power =
> present rpm / peak hp rpm. Since a high-revver has the peak hp at
> a higher rpm, I think it would be more likely than not that you'd
> be further away. Which is the same as what you said about having
> to downshift to get at the hi-revver's power.
>
>
> >But the engine will seem to be more flexible in normal driving, i.e., not
> >requiring gear shifts all the time.
>
> Agreed. Basically, if you want to drive at low rpm, get the big
> displacement engine.
>
> >On the other hand, an engine that produces peak torque at a higher RPM
has a
> >flatter power output curve at the upper RPM's
>
> Again, I do not see this generality as being obviously true.
> Sorry.
>
> Give me two engines with the same hp, but widely different torque
> ratings in otherwise identical vehicles (choose gearing to best
> suit each) and they'll have just about the same best accel
> numbers. But in "normal" driving, most will perceive (scratch
> that, actually get) better accel in the big displacement, high
> torque engine since most will not normally be at the hi revs where
> the hi-revver makes up ground.
>
> Your physics still holds. In *most* "normal" situations, the
> big-torque engine will be making more hp than the hi-revver.
> Unless you consider normal driving to be above 6000 rpm.
My main purpose was to state some laws of physics, to clear up some false,
garbled, or (at best) incomplete statements in earlier posts (Accord vs.
Altima thread).
OK, I went out on a limb writing about car engines. You caught me. Went
looking for evidence... took engine hp & torque ratings from Car & Driver
auto reviews, and made the following table. (If the table is unreadable, set
your newsreader font to Courier and maximize the window...)
Table: Horsepower at Max. Torque for Several Auto Engines
HP, Torque (mfr rating)@ Eng Spd HP @ Max Torque %HP at %RPM
(@Max Torque)
altima v-6
240 bhp @ 5800 rpm 86% of peak
hp at
246 ft-lb @ 4400 rpm 206 hp 76% of
max.HP rpm
pontiac g6 gt
200 bhp @ 5400 rpm 80% of peak
hp at
220 ft-lb @ 3800 rpm 159 hp 70% of
max.HP rpm
accord v-6
240 bhp @ 6250 rpm 84% of peak
hp at
212 ft-lb @ 5000 rpm 202 hp 80% of
max.HP rpm
cherokee v-8
235 bhp @ 4800 rpm 76% of peak
hp at
295 ft-lb @ 3200 rpm 180 hp 67% of
max.HP rpm
scion tc
160 bhp @ 5700 rpm 78% of peak
hp at
163 ft-lb @ 4000 rpm 124 hp 70% of
max.HP rpm
It looks like the engines that make max. torque at lower %RPM make a
relatively higher %HP at that RPM, so this supports your view (I guess...
it's a small sample and there are lots of details ignored...). ***You're
saying that if two engines have identical peak HP @ x-RPM, the one that has
peak torque at lower RPM will (generally) have better usable power output --
give better acceleraction?*** In other words, does this lower peak torque
mean the engine was engineered 'better' for acceleration, given a typical
drivetrain (limited # of gears, no hybrid help) .
Thanks for your input.
---
12-22-2004 | 06:57 AM
#52
Guest
Posts: n/a
Re: Torque vs. horsepower (table repost)
<nospam@none.nul> wrote in message
news:dfdyd.4674$by5.1038@newssvr19.news.prodigy.co m...
>
> "Dave" <dm@nospam.com> wrote in message
> news:Ri3yd.40734$DQ3.40664@twister.nyroc.rr.com...
> > In article <zp2yd.4204$_X7.3909@newssvr33.news.prodigy.com> ,
> <nospam@none.nul> wrote:
Trying again to make the table readable........
Table: Horsepower at Max. Torque for Several Auto Engines
HP, Torque (mfr rating)@ Eng Spd HP @ Max Torque %HP at %RPM
(@Max Torque)
altima v-6
240 bhp @ 5800 rpm 86% of peak
hp at
246 ft-lb @ 4400 rpm 206 hp 76% of
max.HP rpm
pontiac g6 gt
200 bhp @ 5400 rpm 80% of peak
hp at
220 ft-lb @ 3800 rpm 159 hp 70% of
max.HP rpm
accord v-6
240 bhp @ 6250 rpm 84% of peak
hp at
212 ft-lb @ 5000 rpm 202 hp 80% of
max.HP rpm
cherokee v-8
235 bhp @ 4800 rpm 76% of peak
hp at
295 ft-lb @ 3200 rpm 180 hp 67% of
max.HP rpm
scion tc
160 bhp @ 5700 rpm 78% of peak
hp at
163 ft-lb @ 4000 rpm 124 hp 70% of
max.HP rpm
12-22-2004 | 06:57 AM
#53
Guest
Posts: n/a
Re: Torque vs. horsepower (table repost)
<nospam@none.nul> wrote in message
news:dfdyd.4674$by5.1038@newssvr19.news.prodigy.co m...
>
> "Dave" <dm@nospam.com> wrote in message
> news:Ri3yd.40734$DQ3.40664@twister.nyroc.rr.com...
> > In article <zp2yd.4204$_X7.3909@newssvr33.news.prodigy.com> ,
> <nospam@none.nul> wrote:
Trying again to make the table readable........
Table: Horsepower at Max. Torque for Several Auto Engines
HP, Torque (mfr rating)@ Eng Spd HP @ Max Torque %HP at %RPM
(@Max Torque)
altima v-6
240 bhp @ 5800 rpm 86% of peak
hp at
246 ft-lb @ 4400 rpm 206 hp 76% of
max.HP rpm
pontiac g6 gt
200 bhp @ 5400 rpm 80% of peak
hp at
220 ft-lb @ 3800 rpm 159 hp 70% of
max.HP rpm
accord v-6
240 bhp @ 6250 rpm 84% of peak
hp at
212 ft-lb @ 5000 rpm 202 hp 80% of
max.HP rpm
cherokee v-8
235 bhp @ 4800 rpm 76% of peak
hp at
295 ft-lb @ 3200 rpm 180 hp 67% of
max.HP rpm
scion tc
160 bhp @ 5700 rpm 78% of peak
hp at
163 ft-lb @ 4000 rpm 124 hp 70% of
max.HP rpm
12-22-2004 | 08:42 AM
#54
Guest
Posts: n/a
Re: Torque vs. horsepower
In article <dfdyd.4674$by5.1038@newssvr19.news.prodigy.com> , <nospam@none.nul> wrote:
>My main purpose was to state some laws of physics, to clear up some false,
>garbled, or (at best) incomplete statements in earlier posts (Accord vs.
>Altima thread).
Gotcha. And again, I agree with the physics. Torque v HP is one
of the oldest, and even though simple, most misunderstood, auto
forum debates. Part of the problem is in just getting the message
across. Some people know the "truth", but either can't convey it,
or comprehend someone elses discussion of it. But alas, I'd
estimate that more than 50% of the folk screaming about it are
clueless. Physics is the best way, but again alas, >50% are
incapable or unwilling to follow.
>(I guess...it's a small sample and there are lots of details ignored...).
Agreed, probably too small to make any conclusions. And I think
you really have to look at the shapes of the curves. Variable
valve timing, tunable intakes and systems like VTEC (added cam
lobes) are doing a good job of broadening out torque curves. But
there are still peaky hi-revvers (the 2.0L S2000 makes 153 ft-lb
peak torque at ~7600, but off VTEC, ie <5500-6000 rpm, it is c.
135 or less). And crappy low revvers too.
> ***You're
>saying that if two engines have identical peak HP @ x-RPM, the one that has
>peak torque at lower RPM will (generally) have better usable power output --
>give better acceleraction?*** In other words, does this lower peak torque
>mean the engine was engineered 'better' for acceleration, given a typical
>drivetrain (limited # of gears, no hybrid help) .
I was more referring to same hp but at different rpm. Clearly the
hi-revver will be lower displacement with less torque. So if both
are cruising at 3000 and you punch it, the hi-torque one is making
more power (power=torque*3000 rpm), and accelerates better.
But if they have the same peak hp at same peak rpm, but one
has peak torque at lower rpm, then what happens? Hmmmm. Well, if
at lower rpm, then yes, the one with the lower rpm torque peak
will clearly be quicker there. But overall the difference would
be smaller than my case above, probably marginal. All depends on
the shape of that curve. At any given rpm (and given road speed),
the one with more torque is making more power and accelerates
faster.
Tuning an engine for low rpm "drivability" vs high rpm power is a
common tradeoff. And again, I think that's what a lot of this
hi-tech variable valve technology is about. Getting best of both
worlds.
>Thanks for your input.
Welcome, and nice to have a reasonable discussion on this topic
:-)
Dave
>My main purpose was to state some laws of physics, to clear up some false,
>garbled, or (at best) incomplete statements in earlier posts (Accord vs.
>Altima thread).
Gotcha. And again, I agree with the physics. Torque v HP is one
of the oldest, and even though simple, most misunderstood, auto
forum debates. Part of the problem is in just getting the message
across. Some people know the "truth", but either can't convey it,
or comprehend someone elses discussion of it. But alas, I'd
estimate that more than 50% of the folk screaming about it are
clueless. Physics is the best way, but again alas, >50% are
incapable or unwilling to follow.
>(I guess...it's a small sample and there are lots of details ignored...).
Agreed, probably too small to make any conclusions. And I think
you really have to look at the shapes of the curves. Variable
valve timing, tunable intakes and systems like VTEC (added cam
lobes) are doing a good job of broadening out torque curves. But
there are still peaky hi-revvers (the 2.0L S2000 makes 153 ft-lb
peak torque at ~7600, but off VTEC, ie <5500-6000 rpm, it is c.
135 or less). And crappy low revvers too.
> ***You're
>saying that if two engines have identical peak HP @ x-RPM, the one that has
>peak torque at lower RPM will (generally) have better usable power output --
>give better acceleraction?*** In other words, does this lower peak torque
>mean the engine was engineered 'better' for acceleration, given a typical
>drivetrain (limited # of gears, no hybrid help) .
I was more referring to same hp but at different rpm. Clearly the
hi-revver will be lower displacement with less torque. So if both
are cruising at 3000 and you punch it, the hi-torque one is making
more power (power=torque*3000 rpm), and accelerates better.
But if they have the same peak hp at same peak rpm, but one
has peak torque at lower rpm, then what happens? Hmmmm. Well, if
at lower rpm, then yes, the one with the lower rpm torque peak
will clearly be quicker there. But overall the difference would
be smaller than my case above, probably marginal. All depends on
the shape of that curve. At any given rpm (and given road speed),
the one with more torque is making more power and accelerates
faster.
Tuning an engine for low rpm "drivability" vs high rpm power is a
common tradeoff. And again, I think that's what a lot of this
hi-tech variable valve technology is about. Getting best of both
worlds.
>Thanks for your input.
Welcome, and nice to have a reasonable discussion on this topic
:-)
Dave
12-22-2004 | 08:42 AM
#55
Guest
Posts: n/a
Re: Torque vs. horsepower
In article <dfdyd.4674$by5.1038@newssvr19.news.prodigy.com> , <nospam@none.nul> wrote:
>My main purpose was to state some laws of physics, to clear up some false,
>garbled, or (at best) incomplete statements in earlier posts (Accord vs.
>Altima thread).
Gotcha. And again, I agree with the physics. Torque v HP is one
of the oldest, and even though simple, most misunderstood, auto
forum debates. Part of the problem is in just getting the message
across. Some people know the "truth", but either can't convey it,
or comprehend someone elses discussion of it. But alas, I'd
estimate that more than 50% of the folk screaming about it are
clueless. Physics is the best way, but again alas, >50% are
incapable or unwilling to follow.
>(I guess...it's a small sample and there are lots of details ignored...).
Agreed, probably too small to make any conclusions. And I think
you really have to look at the shapes of the curves. Variable
valve timing, tunable intakes and systems like VTEC (added cam
lobes) are doing a good job of broadening out torque curves. But
there are still peaky hi-revvers (the 2.0L S2000 makes 153 ft-lb
peak torque at ~7600, but off VTEC, ie <5500-6000 rpm, it is c.
135 or less). And crappy low revvers too.
> ***You're
>saying that if two engines have identical peak HP @ x-RPM, the one that has
>peak torque at lower RPM will (generally) have better usable power output --
>give better acceleraction?*** In other words, does this lower peak torque
>mean the engine was engineered 'better' for acceleration, given a typical
>drivetrain (limited # of gears, no hybrid help) .
I was more referring to same hp but at different rpm. Clearly the
hi-revver will be lower displacement with less torque. So if both
are cruising at 3000 and you punch it, the hi-torque one is making
more power (power=torque*3000 rpm), and accelerates better.
But if they have the same peak hp at same peak rpm, but one
has peak torque at lower rpm, then what happens? Hmmmm. Well, if
at lower rpm, then yes, the one with the lower rpm torque peak
will clearly be quicker there. But overall the difference would
be smaller than my case above, probably marginal. All depends on
the shape of that curve. At any given rpm (and given road speed),
the one with more torque is making more power and accelerates
faster.
Tuning an engine for low rpm "drivability" vs high rpm power is a
common tradeoff. And again, I think that's what a lot of this
hi-tech variable valve technology is about. Getting best of both
worlds.
>Thanks for your input.
Welcome, and nice to have a reasonable discussion on this topic
:-)
Dave
>My main purpose was to state some laws of physics, to clear up some false,
>garbled, or (at best) incomplete statements in earlier posts (Accord vs.
>Altima thread).
Gotcha. And again, I agree with the physics. Torque v HP is one
of the oldest, and even though simple, most misunderstood, auto
forum debates. Part of the problem is in just getting the message
across. Some people know the "truth", but either can't convey it,
or comprehend someone elses discussion of it. But alas, I'd
estimate that more than 50% of the folk screaming about it are
clueless. Physics is the best way, but again alas, >50% are
incapable or unwilling to follow.
>(I guess...it's a small sample and there are lots of details ignored...).
Agreed, probably too small to make any conclusions. And I think
you really have to look at the shapes of the curves. Variable
valve timing, tunable intakes and systems like VTEC (added cam
lobes) are doing a good job of broadening out torque curves. But
there are still peaky hi-revvers (the 2.0L S2000 makes 153 ft-lb
peak torque at ~7600, but off VTEC, ie <5500-6000 rpm, it is c.
135 or less). And crappy low revvers too.
> ***You're
>saying that if two engines have identical peak HP @ x-RPM, the one that has
>peak torque at lower RPM will (generally) have better usable power output --
>give better acceleraction?*** In other words, does this lower peak torque
>mean the engine was engineered 'better' for acceleration, given a typical
>drivetrain (limited # of gears, no hybrid help) .
I was more referring to same hp but at different rpm. Clearly the
hi-revver will be lower displacement with less torque. So if both
are cruising at 3000 and you punch it, the hi-torque one is making
more power (power=torque*3000 rpm), and accelerates better.
But if they have the same peak hp at same peak rpm, but one
has peak torque at lower rpm, then what happens? Hmmmm. Well, if
at lower rpm, then yes, the one with the lower rpm torque peak
will clearly be quicker there. But overall the difference would
be smaller than my case above, probably marginal. All depends on
the shape of that curve. At any given rpm (and given road speed),
the one with more torque is making more power and accelerates
faster.
Tuning an engine for low rpm "drivability" vs high rpm power is a
common tradeoff. And again, I think that's what a lot of this
hi-tech variable valve technology is about. Getting best of both
worlds.
>Thanks for your input.
Welcome, and nice to have a reasonable discussion on this topic
:-)
Dave
12-22-2004 | 10:12 AM
#56
Guest
Posts: n/a
Re: Torque vs. horsepower
On Tue, 21 Dec 2004 23:33:51 +0000, nospam wrote:
> Found this helpful - http://www.vettenet.org/torquehp.html
>
> Here's my take.
>
> Power rules for acceleration, and a flat power output curve means faster
> acceleration. A flat power output curve is suggested by a relatively
> high-RPM torque peak.
>
> <SNIP>
> Torque x rotational speed does equal power. (Must throw in conversion
> factors when using English units: Power [as hp] = torque [as ft-lbs] x
> rotational speed [as RPM] / 5252.)
>
> In practice, if an engine produces peak torque at a relatively lower RPM,
> the power curve for that engine is more strongly sloped down from peak
> horsepower. It doesn't produce anywhere near the highest horsepower except
> at its peak horsepower speed.
I think you are as-backly-ackwards on this: If HP = Torque x RPM (which it
does, with the fudge-factors you mentioned), then an engine requires MORE
torque at lower RPM to get a "flatter" HP curve. That is, if you want HP
to be more or less constant, you need MORE torque when RPMs are lower.
So, an engine with lots of torque at low rpm will give more hp at the
lower rpm. This will compensate for the fact that, if torgue was constant,
HP goes up with RPM. If torque is achived at a high RPM, then both RPM and
torque are "peaking" at the same time, giving a very "spikey" hp curve.
Now, as you said, the flatter power curve (given by torque at LOW rpm) is
better for smooth driving, fewer gear changes, etc. The "spikey" power
curve gives more hp, since both RPM and torque are peaking at the same
time, but results in lots of gear changes to find that spike.
Lloyd
> Found this helpful - http://www.vettenet.org/torquehp.html
>
> Here's my take.
>
> Power rules for acceleration, and a flat power output curve means faster
> acceleration. A flat power output curve is suggested by a relatively
> high-RPM torque peak.
>
> <SNIP>
> Torque x rotational speed does equal power. (Must throw in conversion
> factors when using English units: Power [as hp] = torque [as ft-lbs] x
> rotational speed [as RPM] / 5252.)
>
> In practice, if an engine produces peak torque at a relatively lower RPM,
> the power curve for that engine is more strongly sloped down from peak
> horsepower. It doesn't produce anywhere near the highest horsepower except
> at its peak horsepower speed.
I think you are as-backly-ackwards on this: If HP = Torque x RPM (which it
does, with the fudge-factors you mentioned), then an engine requires MORE
torque at lower RPM to get a "flatter" HP curve. That is, if you want HP
to be more or less constant, you need MORE torque when RPMs are lower.
So, an engine with lots of torque at low rpm will give more hp at the
lower rpm. This will compensate for the fact that, if torgue was constant,
HP goes up with RPM. If torque is achived at a high RPM, then both RPM and
torque are "peaking" at the same time, giving a very "spikey" hp curve.
Now, as you said, the flatter power curve (given by torque at LOW rpm) is
better for smooth driving, fewer gear changes, etc. The "spikey" power
curve gives more hp, since both RPM and torque are peaking at the same
time, but results in lots of gear changes to find that spike.
Lloyd
12-22-2004 | 10:12 AM
#57
Guest
Posts: n/a
Re: Torque vs. horsepower
On Tue, 21 Dec 2004 23:33:51 +0000, nospam wrote:
> Found this helpful - http://www.vettenet.org/torquehp.html
>
> Here's my take.
>
> Power rules for acceleration, and a flat power output curve means faster
> acceleration. A flat power output curve is suggested by a relatively
> high-RPM torque peak.
>
> <SNIP>
> Torque x rotational speed does equal power. (Must throw in conversion
> factors when using English units: Power [as hp] = torque [as ft-lbs] x
> rotational speed [as RPM] / 5252.)
>
> In practice, if an engine produces peak torque at a relatively lower RPM,
> the power curve for that engine is more strongly sloped down from peak
> horsepower. It doesn't produce anywhere near the highest horsepower except
> at its peak horsepower speed.
I think you are as-backly-ackwards on this: If HP = Torque x RPM (which it
does, with the fudge-factors you mentioned), then an engine requires MORE
torque at lower RPM to get a "flatter" HP curve. That is, if you want HP
to be more or less constant, you need MORE torque when RPMs are lower.
So, an engine with lots of torque at low rpm will give more hp at the
lower rpm. This will compensate for the fact that, if torgue was constant,
HP goes up with RPM. If torque is achived at a high RPM, then both RPM and
torque are "peaking" at the same time, giving a very "spikey" hp curve.
Now, as you said, the flatter power curve (given by torque at LOW rpm) is
better for smooth driving, fewer gear changes, etc. The "spikey" power
curve gives more hp, since both RPM and torque are peaking at the same
time, but results in lots of gear changes to find that spike.
Lloyd
> Found this helpful - http://www.vettenet.org/torquehp.html
>
> Here's my take.
>
> Power rules for acceleration, and a flat power output curve means faster
> acceleration. A flat power output curve is suggested by a relatively
> high-RPM torque peak.
>
> <SNIP>
> Torque x rotational speed does equal power. (Must throw in conversion
> factors when using English units: Power [as hp] = torque [as ft-lbs] x
> rotational speed [as RPM] / 5252.)
>
> In practice, if an engine produces peak torque at a relatively lower RPM,
> the power curve for that engine is more strongly sloped down from peak
> horsepower. It doesn't produce anywhere near the highest horsepower except
> at its peak horsepower speed.
I think you are as-backly-ackwards on this: If HP = Torque x RPM (which it
does, with the fudge-factors you mentioned), then an engine requires MORE
torque at lower RPM to get a "flatter" HP curve. That is, if you want HP
to be more or less constant, you need MORE torque when RPMs are lower.
So, an engine with lots of torque at low rpm will give more hp at the
lower rpm. This will compensate for the fact that, if torgue was constant,
HP goes up with RPM. If torque is achived at a high RPM, then both RPM and
torque are "peaking" at the same time, giving a very "spikey" hp curve.
Now, as you said, the flatter power curve (given by torque at LOW rpm) is
better for smooth driving, fewer gear changes, etc. The "spikey" power
curve gives more hp, since both RPM and torque are peaking at the same
time, but results in lots of gear changes to find that spike.
Lloyd
12-22-2004 | 10:41 AM
#58
Guest
Posts: n/a
Re: Torque vs. horsepower
"Lloyd Sumpter" <lsumpter@dccnet.com> wrote in message
news
an.2004.12.22.15.12.07.520381@dccnet.com...> On Tue, 21 Dec 2004 23:33:51 +0000, nospam wrote:
>
> > Found this helpful - http://www.vettenet.org/torquehp.html
> >
> > Here's my take.
> >
> > Power rules for acceleration, and a flat power output curve means faster
> > acceleration. A flat power output curve is suggested by a relatively
> > high-RPM torque peak.
> >
> > <SNIP>
> > Torque x rotational speed does equal power. (Must throw in conversion
> > factors when using English units: Power [as hp] = torque [as ft-lbs] x
> > rotational speed [as RPM] / 5252.)
> >
> > In practice, if an engine produces peak torque at a relatively lower
RPM,
> > the power curve for that engine is more strongly sloped down from peak
> > horsepower. It doesn't produce anywhere near the highest horsepower
except
> > at its peak horsepower speed.
>
> I think you are as-backly-ackwards on this: If HP = Torque x RPM (which it
> does, with the fudge-factors you mentioned), then an engine requires MORE
> torque at lower RPM to get a "flatter" HP curve. That is, if you want HP
> to be more or less constant, you need MORE torque when RPMs are lower.
>
> So, an engine with lots of torque at low rpm will give more hp at the
> lower rpm. This will compensate for the fact that, if torgue was constant,
> HP goes up with RPM. If torque is achived at a high RPM, then both RPM and
> torque are "peaking" at the same time, giving a very "spikey" hp curve.
>
> Now, as you said, the flatter power curve (given by torque at LOW rpm) is
> better for smooth driving, fewer gear changes, etc. The "spikey" power
> curve gives more hp, since both RPM and torque are peaking at the same
> time, but results in lots of gear changes to find that spike.
>
> Lloyd
Lloyd is right. Dig up a dyno chart for a rotary engine, which produces
almost constant torque at any RPM. The HP is a straight diagonal line
peaking right at redline. It's not the easiest car to drive fast, and
requires careful shifting, but the Formula Mazda drivers don't complain one
bit.
If you want a flat horsepower curve, you need to peak your torque early
and steadily decrease the torque in upper RPMs.
Dave
12-22-2004 | 10:41 AM
#59
Guest
Posts: n/a
Re: Torque vs. horsepower
"Lloyd Sumpter" <lsumpter@dccnet.com> wrote in message
news
an.2004.12.22.15.12.07.520381@dccnet.com...> On Tue, 21 Dec 2004 23:33:51 +0000, nospam wrote:
>
> > Found this helpful - http://www.vettenet.org/torquehp.html
> >
> > Here's my take.
> >
> > Power rules for acceleration, and a flat power output curve means faster
> > acceleration. A flat power output curve is suggested by a relatively
> > high-RPM torque peak.
> >
> > <SNIP>
> > Torque x rotational speed does equal power. (Must throw in conversion
> > factors when using English units: Power [as hp] = torque [as ft-lbs] x
> > rotational speed [as RPM] / 5252.)
> >
> > In practice, if an engine produces peak torque at a relatively lower
RPM,
> > the power curve for that engine is more strongly sloped down from peak
> > horsepower. It doesn't produce anywhere near the highest horsepower
except
> > at its peak horsepower speed.
>
> I think you are as-backly-ackwards on this: If HP = Torque x RPM (which it
> does, with the fudge-factors you mentioned), then an engine requires MORE
> torque at lower RPM to get a "flatter" HP curve. That is, if you want HP
> to be more or less constant, you need MORE torque when RPMs are lower.
>
> So, an engine with lots of torque at low rpm will give more hp at the
> lower rpm. This will compensate for the fact that, if torgue was constant,
> HP goes up with RPM. If torque is achived at a high RPM, then both RPM and
> torque are "peaking" at the same time, giving a very "spikey" hp curve.
>
> Now, as you said, the flatter power curve (given by torque at LOW rpm) is
> better for smooth driving, fewer gear changes, etc. The "spikey" power
> curve gives more hp, since both RPM and torque are peaking at the same
> time, but results in lots of gear changes to find that spike.
>
> Lloyd
Lloyd is right. Dig up a dyno chart for a rotary engine, which produces
almost constant torque at any RPM. The HP is a straight diagonal line
peaking right at redline. It's not the easiest car to drive fast, and
requires careful shifting, but the Formula Mazda drivers don't complain one
bit.
If you want a flat horsepower curve, you need to peak your torque early
and steadily decrease the torque in upper RPMs.
Dave
12-22-2004 | 01:40 PM
#60
Guest
Posts: n/a
Re: Torque vs. horsepower
nospam@none.nul wrote:
> Found this helpful - http://www.vettenet.org/torquehp.html
>
> Here's my take.
>
> Power rules for acceleration, and a flat power output curve means faster
> acceleration. A flat power output curve is suggested by a relatively
> high-RPM torque peak.
>
[snip]
No... you DO NOT want a FLAT POWER curve. Easy to show that
Acceleration = Power / (Mass x Speed)
So if power were constant (Flat) your acceleration would decrease as engine and
car speed increased. The whole idea of modern engine design with all the
variable valve timing etc. is to get a flat TORQUE curve. Because of the
physics of combustion, there is max value of torque you can get from an engine.
It's simply mean cylinder pressure x displacement. So the goal is to get the
torque up as fast as possible at low rpm (by achieving high volumetric
efficiency) and then *holding* it there at high rpm. Power dies when you reach
the rpm where you can no longer fill the cylinders fast enough to keep up
(torque falls)
Some of the previous replies are close - but I hope this makes it a bit more
clear.
Again, ideal IC engine would have a hp curve that is a straight line vs rpm, as
stated by someone previously.
Frank