Horsepower versus torque
- Thread starter Frank
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Chalnoth said:
of course you are. RPMs are not something that can be boosted endlessly. that can be seen as another argument in favor of torque. once one of the factors of the torque x RPM expression hits its physical limits you have little choice but to concentrate on the other.
Yes, I was, a bit. But not much, seen from the chart I posted earlier:chavvdarrr said:
Code:
Weight kW 0-100 Top Fuel Car
1030 66 10.7 175 diesel Toyota Yaris 1.4 D4-D Linea Terra
1000 64 13.1 170 gasoline Toyota Yaris 1.3 16v VVT-i Linea Sol
1215 78 11.2 186 diesel Renault Mégane Sedan 1.5 dCi 105 Privilège
1120 72 12.5 183 gasoline Renault Mégane 1.4 16V Accès
1245 80 10.8 186 diesel Mercedes-Benz A 180 CDI Avantgarde
1095 70 12.6 175 gasoline Mercedes-Benz A 150 Classic
1718 110 11.3 180 diesel Hyundai Santa Fe 2.2 CRDi VGT 2WD AV
1547 99 12.2 174 gasoline Hyundai Santa Fe 2.0i 16V 2WD AV
1263 81 11.5 183 diesel Ford Focus 1.6 TDCi 109pk Trend Automatic
1154 74 10.9 185 gasoline Ford Focus 1.6 16V Futura
1244 80 12.4 192 diesel Citroen C4 Coupé 1.6 HDi 16V 110pk VTR
1249 80 14.6 188 gasoline Citroen C4 1.6 16V Ligne Prestige
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*raises eyebrow* I don't think anyone is suggesting that cars should have a little 1 liter engine that revs to 10 grand to make power.darkblu said:
However, it's not like a car needs 300 pound feet of torque at 2200 rpm just to take someone to work.
Even with a car that does naught to 60 in a wopping 10 seconds, how often do you gun it when a light turns green?
There's really no reason at all to have a crap load of torque at 2000~ rpm, simply overkill for cars.
Every time. And 0-60 in 10s is too slow!radeonic2 said:
Of course there is: freeway driving. In order to have a reasonable amount of power, most of today's small cars are geared to run at rather high RPM's at freeway speeds (3-4k). With diesel engines, they could run at much lower RPM's while retaining the same feeling of responsiveness for the driver, thus resulting in much better fuel economy.radeonic2 said:
scooby_dooby
Legend
Acura Integra Type-R
http://www.edmunds.com/used/1997/acura/integra/17172/specs.html
0-60 - 6.5 seconds
130ft-lbs of torque @ 7500 rpms
http://www.edmunds.com/used/1997/acura/integra/17172/specs.html
0-60 - 6.5 seconds
130ft-lbs of torque @ 7500 rpms
ShootMyMonkey
Veteran
I never said that. I'm saying Gasoline is far further from "magic." If you didn't notice, (and you've pretty much shown with this post that you haven't and never could have anyway), I've pretty clearly said that there are plenty of things out there that are superior to both, but they simply don't exist.
The problem with this statement is that mileage-derived emissions are the only valid means of measuring because there isn't a soul on the planet who drives "by power" or "by cubic meters of exhaust", but by distance. Observed fuel consumption and emissions by mile is indeed related to the power curve, and always will be.
And your arguments about CO2 emissions make me wonder if you've ever heard of biodiesel. The fuel and the method of combustion are two different things. And even otherwise, I'd value my money far more than the environment any day of the week. Global warming certainly exists and all, but I'll be dead before anybody does anything about it anyway. So will you and everyone else responding to this thread.
I dismiss them because they don't apply to the cases I'm concerned with. I don't give a damn about rally races and dragstrips and F1, and never will. Sure there are drawbacks, but where do they matter? Everywhere where the existence of a vehicle can be described as nothing more than a frivolous waste of time and money.
scooby_dooby
Legend
DiGuru said:
Point is: Lowend torque is not necessary for good acceleration, even off of the line.
Mintmaster
Veteran
Show me fuel economy and 80-120 km/h figures (or whatever the mph equivalent standard is for passing acceleration) for a diesel engine and I'll believe you.Chalnoth said:
Better fuel economy for diesels has more to do with energy density. Significantly better fuel economy for high-torque, low-revving engines is a myth. The only way you see that is if the high-torque engine isn't as good at freeway acceleration, in which case your comparison is invalid. TDI's, for example, are terrible for highway passing, but fine from a standstill in the city.
Friction during acceleration is all you save with a high-torque engine. That's a very tiny percentage of any ordinary car's expenditure of energy on the freeway.
Anyway, I'll say it one more time: acceleration depends on power, not torque, of an engine. Diesel engines are indeed a bit more efficient, but it has very little to do with torque.
haha.. great for fuel economy.RussSchultz said:
With traffic it's pretty much impossible to gun it unless you're the first to the light, even with a car that does 0-60 in 20 seconds (I had a beetle).
Btw I said wopping in jest, it prolly wasn't clear to you because that chart someone posted withall those those slow cars.
Because changing up a gear or two is too hard?Chalnoth said:
On the freeway you shouldn't be doing much acceration either besides passing, and in that case you might wanna get up to speed quickly and a gear change helps for that, even with a silly diesel.
I maintain that low end torque (peaking at around 2000 rpm) is really only good for big heavy trucks/suvs.
On the freeway cars can still have gearing that allows for crusing at 60-75~ around 2000 since you need so little power
Mintmaster
Veteran
As I mentioned before, the power curve is for an optimal fuel mixture (by optimal I mean that yielding the most torque). Optimal fuel economy is not generally obtained while operating on the power curve. Here's a BFSC graph, for example. The torque curve is the solid blue line, and you can translate that into a power curve. Optimal fuel economy is not obtained there. For any given load (the constant power curves), you want to choose the gear (which affects the x-coordinate) and fuel:air ratio (which affects the y-coordinate) to minimize BSFC.ShootMyMonkey said:
Fair enough, but the fact that diesel gives you more usable energy per dollar is a tangential argument. On its own, a higher torque equal power engine has few advantages, especially considering that it'll only help standstill acceleration and will be heavier/bigger also.
About biodiesel, I don't know much, but here's what I found from wikipedia:
There are possibilities for drastically increasing vegetable/bio oil production, but they will remain possibilities for a long time. It'll barely make a dent in emissions.
DuckThor Evil
Legend
Mintmaster said:
I have to disagree with this as acceleration on high gears/low reps is the one thing that TDI's are really good at, thus at high way speeds they get good acceleration with highest gear.
Of course it matters to what we compare it. I don't think comparing 2 liter turbo diesel to 2 liter natural aspirated gasoline engine is a valid comparison, if you bolt in turbo to that gasoline engine things don't look the same anymore. Nice example of gasoline turbo is Volvo 2.5 liter low pressure turbo which in Volvo S40 T5 model gives 220hp and 320nm of torgue at 1500-4800rpm
and diguru nicely cherrypicked entry level models that make your arguments look decent, which they are not btw. Manual 1.6l C4 goes from 0-100 at 10.6 not 14.6 like you mentioned for example.
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It's not about the driver in this instance. It's about how the car is geared coming out of the factory. Cars with smaller engines are typically geared to run at rather high RPM's in the highest gear at freeway speeds. This is, of course, done to make the car feel responsive. You'd get the same feeling with a higher gearing in a diesel.radeonic2 said:
Are you talking about economy cars with like 1.6~ liter engines or moderate cars with engines in the 2 liter range?Chalnoth said:
If you're talking about cars with like 1.3 engine, then sure, but in that case a diesel car would prolly run a bit more wouldn't it?
I don't know of very many diesel economy cars in the us.
