Horsepower versus torque

[mjtdevries]

to those fellows who were wondering earlier what high torque is good for in a performance car (i.e. not discusing towing, apparently) - rally tunings tend to maximise torque. i.e. in driving where you get too numerous slow-down/near-stand-still situations, or what some call 'technical driving', and you have high dynamics of the RPM which close- or super-close gears alone cannot handle, you want high torque. and then sometimes you cannot afford very close gears (when you still want that vmax) but you are still in a high-dynamics RPM situation.

so next time before dissing torque get your ass on a rally course : )

Now explain why WRC engines are not diesels...
After all, that was what this thread was really about!

Tuning an engine that is restricted by all kinds of rules, is something completely different from choosing an engine when you have no rules to think about. You should not simply apply the methods of the first situation to the second situation.

 

[darkblu]

Now explain why WRC engines are not diesels...

prohibitively expensive for rally purposes? a diesel that'd be fit for ralling would be significantly more expensive than its gass counterpart (as it'd have to meet the same weight, durability and maintainability requirements). now factor in FIA's homologation rules and enjoy the prospects of having to produce many of that engine.

ask yourself would have audi come up with that fancy diesel for the R10 if they had to follow homologation rules.

 

[MPI]

prohibitively expensive for rally purposes? a diesel that'd be fit for ralling would be significantly more expensive than its gass counterpart (as it'd have to meet the same weight, durability and maintainability requirements). now factor in FIA's homologation rules and enjoy the prospects of having to produce many of that engine.

No, it's because diesels aren't particularily suited for that. Simple as that. Too heavy, too little power.

ask yourself would have audi come up with that fancy diesel for the R10 if they had to follow homologation rules.

Hell no. The R10 is a marketing gimmick anyway, promoting TDI technology, as a lot of cars sold here in Europe are turbodiesels. Not that Audi's accomplishment in Le Mans isn't impressive, but it isn't an end-all argument that diesels are the superior technology. The LeMans technical regulations are pretty intricate, with sometimes weird outcomes... Take the early '90s Mazda 787B Le Mans winner for instance... Comparing displacements between rotary and piston engines can be ...troublesome.

 

[ShootMyMonkey]

prohibitively expensive for rally purposes? a diesel that'd be fit for ralling would be significantly more expensive than its gass counterpart (as it'd have to meet the same weight, durability and maintainability requirements). now factor in FIA's homologation rules and enjoy the prospects of having to produce many of that engine.

I'd also add that a lot of companies which participate in WRC races actually do trickle down their work in that field to the market at large. Something that used to be true of NASCAR and Indy/F1/etc., but probably never again. Nowadays, it takes an enthusiast to even be able to differentiate an F1 car from an Indy car from a Champ car. So-called "stock" cars are anything but stock, and almost all visual distinction between vehicles is virtually non-existent.

In any case, the fact that they have to worry about market/aftermarket units means that the usage is also affected by the fact that diesel has a pretty low penetration in the market outside of Europe.

Too heavy, too little power.

For equal fuel consumption rates again gas engines (and displacements and F/I or NA or whatever all suitably equal), there is nothing you could have said that is further from the truth. More compression and more complete combustion from a longer hydrocarbon is more power.

Yes, you can't rev a normal diesel way up into the higher rpm range like you could do with a gas engine, but the notion that you need to go into high rpms to make power is driven solely by the indoctrination of gasoline spark combustion. Everybody seems to think you need to be able to reach 12,000 rpm to make major power, and that's just the thinking because gasoline engines make garbage at low rpms.

I'd rather be making 100 hp at 2500 rpm than make 180 hp at 7500 rpm... The simple reason why I have the latter is because any philosophy to which I subscribe is inherently precluded by the doctrine which dicates that my bank balance be greater than zero.

Not that Audi's accomplishment in Le Mans isn't impressive, but it isn't an end-all argument that diesels are the superior technology.

I don't see how if racing is not a benchmark for the capabilities of a diesel, people still feel free to use racings conditions to prove that gasoline is superior. I thought the original point of this thread was about how suitable it is for the John Q. Publics. It's actually quite easy nowadays

If it were a matter of simple superiority, then future technologies like HCCI, fuel cells, epielliptical rotaries, cam track riders like the Ox2 engine, and so on. Many of these are superior to both gasoline and diesel, but I don't see the likelihood of any of them hitting the market within the next decade.

 

[darkblu]

If it were a matter of simple superiority, then future technologies like HCCI, fuel cells, epielliptical rotaries, cam track riders like the Ox2 engine, and so on. Many of these are superior to both gasoline and diesel, but I don't see the likelihood of any of them hitting the market within the next decade.

totally agreed. there's nothing 'ultimate' in gas engines aside from the fact that as of now they're the most popular, ergo most explored, and exploited, auto-power tech.

this early prototype electromobile (some specs here, unfortunately in japanese) would slap silly most "performance"-specs, NA or extra charged (no matter how) combustion engines. until you factor in productin cost, that is.

 

[Moloch]

vmax is a concern on the road? High torque is hardly all that different from having higher horsepower sooner, and TDI engines make a far flatter power curve than all the power whores seem to believe. Many of the complaints people have, I'd totally agree with if this were 1997 or so.

If you want high-end power, then get yourself a gas turbine. Their power still grows all the way up past a few tens of thousands in the rpm range. They're also most efficient up there, too (recuperators and all assumed as a given).

In road racing it is, but wrc cars never come close to hitting their drag limited max speed (true vmax), where as road racing cars on tracks with long straights get much closer so having close gears isn't a concern, even where a road racer hits 200mph, they usally have 6 gears so there's no worry of the engine falling out of the torque curve.
When you only need to hit about 130mph you don't need wide spaced gears
Btw, who said low end torque was different then low end hp?
Anyone who doesn't understand that basic concept needs to leave the discussion and never enter another untill they understand that
Have you ever seen a torque curve from a large gas engine?
Great examples are the current 7 liter corvette z06 and 8.3 viper?
The torque curves on those are quite flat
Even smaller ohc engines have pretty flat torque curves now that varible valve timing is so common so they can make high rpm power and not have a shitty idle and needs to be revved above 3000 rpm or above to really work ok.
That solves the problem of a small engine doing that whole "nothing nothing nothing WHOAHHHHHHHHH" torque curve but of course they still don't make some torque.
The 350z though is quite nice, makes good hp and torque per liter but still has a nice torque curve.
TDI's are nice for gas milage but there's simply no reason for them in sports cars, and it's not like they need the low end torque since on the street most people don't race and in racing low end torque doesn't play a large roll at all since you're always going atleast 30mph or so.
A better argument might also be the fact that TDI engines weigh more than gas engines so you can upset the balance with a TDI engine.
You can increase torque with numerically higher gears, you can't increase horsepower that way

Notice I didn't respond to the gas turbine comment?
Why bring up something that isn't exactly what you call common automobiles?

 

[Frank]

So, what would you all suggest for the best price/performance curve for daily use?

 

[darkblu]

So, what would you all suggest for the best price/performance curve for daily use?

considering that your price/performance is proportional to your power/weight ratio:

dunno about you but i'd take a ginetta g4, possibly the late dare verison with a 1700cc Kent engine and twin Weber 40 DCOEs, fitted with a 5 speed sierra gearbox for about 16K quid any day of the week.. if i had the cash, that is

 

[RobertR1]

So, what would you all suggest for the best price/performance curve for daily use?

good low end torque building upthat turns into a flat torque for smooth acceleration through the mid and upper RPM changes.

 

[Moloch]

So, what would you all suggest for the best price/performance curve for daily use?

Not a TDI
depends how much hp you need for "daily" use, for something with 200-250hp, turbocharged 2~ liters seem to work good enough.
Of course they have "lag" untill the threshhold rpm is reached where it can spool the turbo good.
I',m not sure how much a high revving 4 costs to make, I'm not sure how that compares to a 2~ liter that has been beefed up for forced induction use.

 

[WhiningKhan]

Not a TDI
depends how much hp you need for "daily" use, for something with 200-250hp, turbocharged 2~ liters seem to work good enough.

Okay, everybody has the right to define what they 'need'.
The cultural differences between US and other countries, regarding cars, are amazingly deep, as threads like this prove. I think we'd have to swap the places where we live for a year to be able to appreciate the differences.

But turbocharged 2 liter is at least a step towards reason.

Of course they have "lag" untill the threshhold rpm is reached where it can spool the turbo good.

So you complain that you have get revs over 2000 rpm on turbo to get things going? How's that worse than having to get revs over 4-5000rpm on a normally aspirated engine?

 

[Moloch]

Okay, everybody has the right to define what they 'need'.
The cultural differences between US and other countries, regarding cars, are amazingly deep, as threads like this prove. I think we'd have to swap the places where we live for a year to be able to appreciate the differences.

But turbocharged 2 liter is at least a step towards reason.



So you complain that you have get revs over 2000 rpm on turbo to get things going? How's that worse than having to get revs over 4-5000rpm on a normally aspirated engine?

We've used turbocharged 2 liters in the us for some time- see DSMs.
I said over 3000 and I wasn't comparing it directly to a high revving engine.
High revving engines can be fun since they possess superior throttle response to turbocharged engines.
A turbocharged 2 liter engine isn't going to make full power in 1st gear because the power isn't instantly available as it is with n/a cars.
Even when you nail the gas in 3rd gear doin 50 you're not going to have the full 250 or whatever footpounds untill it spools up.
That's technically called turbo lag, turbo lag is NOT when you're in high gear and the engines doin like 2000 rpm and you nail it and it takes a while to spool the turbo, thats because it's below the threshhold rpm, like sort of mentioned before.
So not having the throttle response of an N/a engine is a negative.
A nice n/a 6 banger like the 350z is a good setup for a 274 or 300HP engine.
Though I will say a wrx STI (300hp turbo 2.5 liter) with it's adjustable center differential is a better for pure performance.
To go off topic.. normally AWD is done the quick and dirty way using a vicious coupling center diff with a 50:50 split which means it's FWD untill the wheels slip and the center "senses" that and trys to even out the speed differences and that results in power on understeer, with the STi and it's adjustable diff you can make it act like a RWD car with the 35:65 torque split.

 

[MPI]

For equal fuel consumption rates again gas engines (and displacements and F/I or NA or whatever all suitably equal), there is nothing you could have said that is further from the truth. More compression and more complete combustion from a longer hydrocarbon is more power.

No, it means higher efficiency. That's not the same thing as power.

Yes, you can't rev a normal diesel way up into the higher rpm range like you could do with a gas engine, but the notion that you need to go into high rpms to make power is driven solely by the indoctrination of gasoline spark combustion. Everybody seems to think you need to be able to reach 12,000 rpm to make major power, and that's just the thinking because gasoline engines make garbage at low rpms.

I'd rather be making 100 hp at 2500 rpm than make 180 hp at 7500 rpm... The simple reason why I have the latter is because any philosophy to which I subscribe is inherently precluded by the doctrine which dicates that my bank balance be greater than zero.

To make "serious" power you DO need rpms. Power = torque x revolution speed, remember? The torque is a function of displacement and, if present, forced induction overpressure.

If you can't increase rpm, you have to increase either displacement or boost pressure, which means either a stonking big engine(heavy) or a stonking big turbo/compressor(higher pressures which means more wear et.c.).

I don't see how if racing is not a benchmark for the capabilities of a diesel, people still feel free to use racings conditions to prove that gasoline is superior. I thought the original point of this thread was about how suitable it is for the John Q. Publics. It's actually quite easy nowadays

It's not a benchmark if the playing field isn't level, hence the Wankel engined Mazda 787B reference...

Where do you draw the line in a Wankel/Diesel/Petrol engine equivalency formula, really? It's really, REALLY hard, actually... I mean what diesel engine configuration does a 3,6l V8 petrol engine compare to? At what boost? At what intake restriction?

If it were a matter of simple superiority, then future technologies like HCCI, fuel cells, epielliptical rotaries, cam track riders like the Ox2 engine, and so on. Many of these are superior to both gasoline and diesel, but I don't see the likelihood of any of them hitting the market within the next decade.

Look, TDIs certainly have a market and are useful, I'll probably get one myself if my current employment continues(160km/day commute), but all this praise of them in this thread is getting a little bit ridiculous, that's all I'm saying. The top five reasons for getting a TDI is:

1. Fuel economy
2. Fuel economy
3. Fuel economy
4. Cheaper fuel
5. Not as horrible as diesels used to be

That does NOT mean that they are superior to petrol engines, which run smoother, have better power/weight ratio, are more "fun", sounds better et.c. It's a question of _compromise_. Just keeping it real, you know...

 

[nthd]

...
1. Fuel economy
2. Fuel economy
3. Fuel economy
4. Cheaper fuel
5. Not as horrible as diesels used to be
...

In nomine Patri et Filii et Spiritus Sancti. Amen.

 

[Mintmaster]

You'll notice those were two different contexts. The highway point was a second case. But then, I guess the concept of multiple contexts in the space of two whole sentences is casting pearls before swine in this case. And I can't recall the last time I've ever seen a road of any kind, highway or not, that wasn't plagued by congestion at some point.

And clearly I am addressing the second point, dumbass. The one to which 80% of RobertR1's paragraph was devoted to.

I fail to see why you need performance when you're "plagued by congestion". Performance is for the open road when you're not endangering others by driving like an idiot in traffic.

Since when does any gasoline engine make higher torque at low RPMs? With diesels or electric motors or turbines, sure... The point is that torquier engines have a power/torque band that is lower in the rpm range. You know, I'm failing to see the actual *superiority* of the idea of putting the powerband in the 5000 or 6000 rpm range as opposed to having it in the 2000 or 3000 rpm range.

If these two engines output the same power, then engine A needs to generate less than half the torque at 5000 RPM of engine B at 2000RPM. Thus a smaller engine can be used.

Check your units. They come out the same. Rotational speed is simply a frequency measurement, meaning it is the inverse of time.

It doesn't matter if the units are the same. Is distance equal to acceleration times the square of time? Is torque the same as work? You said power is delivered torque per unit time. That sentence makes no sense. Apply a torque of 100 Nm for 20 seconds and it tells you nothing about power. Apply it over a rotational distance of 10 radians in a second and then you average 1kW over that time span.

Exceptionally wrong. This would be true if one engine being higher torque than another was purely an ephemeral thing. The fact is that the characteristics of combustion need to be fundamentally different. That's kind of the point behind bringing up diesels at the beginning of this thread in the first place.

And how does this make my statement "exceptionally wrong"? At a given RPM, if one engine is generating more torque, then it is consuming more gas unless you handicap one by not burning efficiently. Even throwing in diesel, it only gives you higher torque than gasoline (at equal fuel consumption) because it has a higher energy density, which also means higher emissions per litre anyway.

There's no free lunch here. If diesel gives you twice the torque at 2000RPM, it consumes nearly twice the gas, and emits twice the emissions.

Yes, it's apples and oranges. I wasn't getting into saying that apples and oranges have similar properties -- it was a matter of which is more beneficial? Apples or Oranges? In the case of the apple being a diesel and an orange being gasoline engine, I don't see any advantage off of the racetrack for picking the orange. You can't help but overexaggerate the weaknesses because there isn't a case of a counterargument anywhere in this thread by you or anyone else that actually lies in middle ground. You can't really help it if you've been indoctrinated.

I don't have enough data to say whether gas or diesel is better. The point is that performance is determined by power, not torque. DiGuru is incorrect with his assertion in his original post.

Are you aware that CVTs are rarely tuned for performance and generically tuned for efficiency?

There is no single tuning for a CVT. If you mash the pedal then the CVT will adjust the gear ratio so the engine stays in the powerband regardless of speed, hence optimizing acceleration. If you're gentle on the pedal and just maintaining speed, it'll keep the revs in the range for optimal efficiency.


Anyway, the point of everything I said is that acceleration is determined by horsepower, not torque. It doesn't matter if you're talking about gasoline, diesel, turbine, electric, whatever. That is what this thread is about.

The only reason the details of the power curve matters (which peak torque lets us know a bit about) is that we don't have infinite gears. Thus a high torque engine sometimes has benefits starting from a standstill when compared to an equal power lower torque engine.

 

[Frank]

normally AWD is done the quick and dirty way using a vicious coupling center diff with a 50:50 split which means it's FWD untill the wheels slip and the center "senses" that and trys to even out the speed differences

A 50:50 split means that all the wheels get the same amount of power. So it's not FWD. It's AWD.

 

[Frank]

There is no single tuning for a CVT. If you mash the pedal then the CVT will adjust the gear ratio so the engine stays in the powerband regardless of speed, hence optimizing acceleration. If you're gentle on the pedal and just maintaining speed, it'll keep the revs in the range for optimal efficiency.

The links of the CVT belt tend to shatter if the amount of power applied is too high. So, they are tuned to operate in the safe zone, especially for higher power applications (ie. any American car ).

If you put a CVT on a V8, it will have to be a tiny V8, or it will NEVER rev into it's power band.

And delivering maximum power is very bad for your mileage. If you would be able to have a high-power, large and/or turbocharged gasoline engine produce it's peak power all the time, you would have to attach some huge gasoline tank to the car.

Rather, they operate the engine at the most fuel-efficient speed, and increase or decrese the ratio a bit for accelerating/decelerating. Which is a total waste of that high-power gasoline engine in the first place, even if the CVT belt could take that power.



So, what would be the best way to put such a marvelous thing as a CVT to good use, I wonder?

 

[Moloch]

A 50:50 split means that all the wheels get the same amount of power. So it's not FWD. It's AWD.

You're right, but that's only when the front wheels slip. when they aren't it's FWD.
It's a FWD based AWD system
Do you know how a viscous coupling differential works?
Heres a bit from musclecarclub.com

Under normal conditions, both sets of plates and the viscous fluid spin at the same speed. When one set of wheels tries to spin faster, perhaps because it is slipping, the set of plates corresponding to those wheels spins faster than the other. The viscous fluid, stuck between the plates, tries to catch up with the faster disks, dragging the slower disks along. This transfers more torque to the slower moving wheels -- the wheels that are not slipping. The faster the plates are spinning relative to each other, the more torque the viscous coupling transfers. The coupling does not interfere with turns because the amount of torque transferred during a turn is so small. However, this also highlights a disadvantage of the viscous coupling: No torque transfer will occur until a wheel actually starts slipping.

 

[Frank]

You're right, but that's only when the front wheels slip. when they aren't it's FWD.
It's a FWD based AWD system
Do you know how a viscous coupling differential works?
Heres a bit from musclecarclub.com

Nope.

It consists of two, separate things: a differential, and a viscous limited-slip coupling. The differential will do the same thing as what it does between the two front or back wheels: split the torque in both directions. But when one of the wheels start to slip, you lose all power on the wheel that still has traction.

That's why you want to add a coupling that limits the slip. That locks the differential as long as one of the wheels is slipping.

So, yes, the viscous limited-slip coupling will only transfer torque when one of the wheels starts slipping. But when none of the wheels slip, the differential(s) delivers torque to all of them.

 

[Moloch]

Nope.

It consists of two, separate things: a differential, and a viscous limited-slip coupling. The differential will do the same thing as what it does between the two front or back wheels: split the torque in both directions. But when one of the wheels start to slip, you lose all power on the wheel that still has traction.

That's why you want to add a coupling that limits the slip. That locks the differential as long as one of the wheels is slipping.

So, yes, the viscous limited-slip coupling will only transfer torque when one of the wheels starts slipping. But when none of the wheels slip, the differential(s) delivers torque to all of them.

And how is that not make it FWD untill the wheels slip?
Only the front wheels are getting power untill there is a difference in wheel speed between the front and rear wheels.
I really don't see why you're trying to argue about this.