hedgecore

Your statement seems to be made from a somewhat limited viewpoint.

The performance of a car is related to having torque and HP ratings appropriate to many of the properties that define it...you seem to be ignoring some of the limitations of engineering in modern vehicles.

Power is not more important.

Deslock

Your post is written in an eloquent style, but I can't figure out what it's actually trying to say. Then again, reading comprehension was never my strong point...

Can you elaborate? Also, was there something in my other post that you disagreed with?

As I indicated before, at low vehicle speeds high engine torque is desirable. That situation is precisely due to engineering limitations (with gearing, etc). There are other times when extra engine torque can be convenient (say, if you don't like downshifting to pass). And some people like the predictability of a flat torque curve. But in general power is the more important attribute when it comes to acceleration.

BaronVonBigmeat

I think he is trying to say that a "torque" motor may be more desireable than a RPM motor, depending on the application, because of the side effects of each approach.

ie, heavy trucks tend to make HP with big torque, because who wants a short-lived, blazing hot, screaming engine cranking a granny gear at 10,000 RPM's?

Likewise, hardly anyone on a sport bike wants a fat heavy slug of a low-RPM diesel. It could make a bike move fast, but the benefits don't outweigh the costs--for this application. Even a slight weight increase here will have big effects on performance.

Of course, all of these are things outside the purely mathematical definitions of torque, RPM, and HP--they are "things which are usually associated with torque (or RPM ), on current design otto cycle engines". But then again, if someone invents a cheap turbine with good throttle response, every semi would use them, regardless of their gazillion-RPM redline. Likewise, if someone invents a torque monster the size of a cuisinart (quasiturbine, anyone?), plenty of sport bikes will use them. If you're just looking at performance numbers though--whether acceleration, top speed, or towing capacity--HP is what matters (assuming otherwise identical cars).

therm8

Sorry, thought that quote came from my second post.


Power cannot make torque. Power is work with respect to time. You cannot cause work (moving the car) in this case without the torque. Power is basically how much work the engine, and therefore the wheels, causes via the tires in a given amount of time (through torque). An engine that produces zero torque, cannot produce power.

Deslock

None of that contradicts what I wrote:

Deslock

That's true. But in the context of what makes a car accelerate, it's irrelevant that you want big diesels for heavy trucks.

hedgecore

My point is that you seem to be ignoring the assumptions of current technology...you're high HP, low torque motor works well, but there are limitations to how many gears can be efficiently implemented into a vehicle...in any 4-7speed transmission on a car engineered to pass crash tests and sold to consumers, torque is a desirable variable in determining a cars performance...

A well designed car will have an adequate and balanced amount of both based on it's design...

P.S. I'm not trying to be a dick...i'm genuinely curious...how well versed are you in physics?

therm8

Perhaps not, but you seem to be implying that horsepower is doing all the work, when in fact it is not. Your points are all based on gearing, which is used to make better use of torque output to provide more work per time, and have no relevance to the points I am trying to make.

BaronVonBigmeat

Ummm...you aren't providing more work per time with gearing. Gears can trade high torque/low RPM output for low torque/high RPM output, and visa-versa*. But the output (total work done per time) remains the same. I think maybe you meant to type:

"Your points are all based on gearing, which is used to make better use of power output to provide more torque or RPM's..."





* That's why quoting torque numbers (or RPM numbers, if you're a ricer) just doesn't tell a complete story of what an engine's capable of. Wow, you have an engine with 500 ft.-lbs. of torque. Surely it will tow more weight and go faster than the car with 400 ft.-lbs? Well...we don't know. We just don't have enough information (namely, RPM's). It's sort of like assuming that the guy with lean muscular legs will win the footrace, without considering his lung capacity, for example.

If only there were an engineering number that we could use...something that factors in torque, but also RPM's too...then we could really make a fair comparison between two engines!

globi

I doubt it's just because of gearing. The reason why cars with more low-end power are desirable is because, they are more driveable, less noisy and more efficient (less frictional losses).
Also high spinning engines weigh less, which is great but unfortunately most costumers don't care about curbweight (nor do car manufacturers for that matter).

Also if car manufacturers would introduce a low end hp number instead of torque (eg. 100 HP at 3000 rpm) and would talk about linear hp curve instead of flat torque curves, there weren't all these endless torque hp threads.

hedgecore

Agreed, it's all about the engines output pattern...a simple way of putting it comes in the shape of the curve and the total area under the curve.


Bottom line, a quest for only high HP numbers isn't the right quest.

hedgecore

On Gearing...my point was that if we could easily and efficiently devolop transmission with lots of gears and a good way of selecting them, then a high HP motor with little torque would be appropriate.

But, we're stuck with 6 speeds and huge shifting costs...hence the need to reach for a proper balance of HP and torque behavior from an engine.

globi

Actually you don't need more gears with a high end power engine than with low end power engine. In fact most cars with Diesel engines have a very narrow usable power bands. The RX-8 on the other hand has a huge usable power band. Of course in order to get somewhere you need to operate the engine at max power as well. But it doesn't really matter whether max power is at 2000 rpm or 9000 rpm as far as gearing is concerned.

The only way to get rid of gears is by having an engine with a flat power curve.

And of course there are gearboxes with lots of gears:
http://cvt.com.sapo.pt/performances/CVT_vs_MT_calc.htm
There should be a semi manual CVT that allows you to operate it at max power or max economy or anything in between. Substitute the stick with a lever (that can be moved from max power to max economy).

hedgecore

CVT isn't an efficient replacement in performance vehicles...won't be for quite awhile...perhaps with new manufacturing techniques and space aged materials. But yes, when they come we'll see a whole new range of performance engine behavior.

"space aged"...wow, i feel like an info-mercial, haha

hedgecore

Correct. I'm with you on that.

You're talking about high end vs low end.

I mentioned a high hp, low torque engine.

globi

CVTs are also a marketing issue. Many people wouldn't want to drive a sports car at a constant rpm.
Maybe if the FIA hadn't banned it in 1994 it would be more popular.

NomisR

Driving around all the time at 8500RPM in a rotary car isn't so bad. :D

zoom44

there are currently CVTs with selectable ratios

globi

But they all come with torque converters or don't they? A sports car should have a CVT with a clutch (similar to SMG, DSG or whatever they're called.)

zoom44

oohhhhh no they are autos. there is no manual cvt

therm8

check this cvt out: Seems to overcome alot of the inefficiency problems.


http://www.andersoncvt.com/howitworks.html

hedgecore

Wow, that's mad clever! It's clearly no where near ready for serious applications. but, i'd like to see one with a bit of japanese engineering behind it

BTW, someone mentioned that consumers wouldn't be thrilled by transmissions that do not have discreet gears...

Personally, i get a much bigger feeling of excitement from a snowmobile's acceleration than i have from any car(maybe ferarri's, but that's more about the whole experience). I think a CVT in a sports car would totally blow away most enthusiasts idea of what they think fun is!

Again though, i hear SMG's are still getting a bad rap from "car people"...that's kind of sad. If SMG's, which are clearly better performers than standard transmissions can't win people over, how will CVT's?

Japan8

Easy... some people just don't care about the "on-paper" benefits and more about the Overal driving experience. I hate SMG, auto, etc. Boring, feel disconnected from the car.... the driving experience. Like the Lexus IS 350 vs BMW 330is... on paper the Lexus looks like a winner, but once you get behind the wheel... the difference is stark.

globi

As I said SMGs and CVTs might not be accepted by everybody, but they wouldn't be used in racing if they were just better on paper.

hedgecore

Agreed...i must admit, driving the BMW M3 SMG was a bit hard to get used to...for the first few weeks my "clutch foot" would feel around for things to do durring shifts...shifts somehow seemed slower and i felt a bit disconnected.

However, now after learning how it feels, knowing what to expect and realizing the benefits(shifts much faster than even a pro driver) i'm dissapointed more manu's don't offer it as an option. It actually doesn't disconnect you from the car...it immerses you more deeply into it!