no, shadohh, i think you're right. i agree with you. that's what makes hp a useful measurement; is that it's torque as a multiple of rpms, which gives you, perhaps less torque/revolution, but more torque/min.

 

Alright, I'm no expert, but what I understand is that HP and torque are both measurements of power. You can use equations to derive one from the other, because they measure the same thing, power. Their applications however, are different. HP is for top end power, whereas torque is for low end power. Torque gets you started, but HP keeps you going. Torque determines how fast you start, but HP determines how fast you can go. Torque is for acceleration, HP is for top speed. That's why you need a balance. If you have gobs of torque, you'll reach your top speed quickly (assuming a perfectly linear curve), but your top speed will be lower. Conversely, if you have massive HP, you'll have a crazy top speed, but it'll take you forever to get there. Neither one is the answer. You need lots of both to win races, not just torque, and not just HP.

I hope this simplified things. It turned out to be kinda lengthy, but I think it's all correct.

 

is there anyway to make this post sticky so that all people can read it for the rest of there live as to understand the concept of POWER?

 

you're somewhat on the right track, alacritan. except that if i had 750 lb-ft of torque in a big block, supercharged v8 from 1500-4500 rpms, this yields 642 hp, which doesn't seem like a lot of hp for such a torquey engine. however, if i threw some really tall gears in the tranny, i would think that all of the "twist" the engine creates is just as useful in turning those tall gears as hp would be, thus giving it a nice top speed. this is why cvt transmission is so useful; you can always have the right gear to keep the engine in the optimum place for whatever the purpose is.

 

to bad CVT is a noisey ****ing transmission. And is not yet usable in high HP applications. I think over 200hp its breaks.

But I am sure they are working on making it usable in higher horsepower.

 

actually, nissan, mazda, and audi all have cvt's that can withstand around 275 pounds of torque.

 

Lets say you have an engine with constant torque. 100 ft-lbs, no matter the rpms.

Using the formula hp = (torque x rpm)/5252 from above, we get the following "chart".

RPM HP
1000 19
2000 38
3000 57
4000 76
5000 95
5252 100
6000 114
7000 133
8000 152
9000 171

If the torque is contant, the HP only depends on the rpms. How high the rpms can go is highly dependant the engine design. Something will eventually melt due to heat, or wear out from friction, or the valves will start bouncing or something.

Now lets introduce a little more reality into the situation. Torque curves are not gonna be strait. How the engine is designed / tuned will dictate the shape of the torque curve. Different properties of the drive train, the intake, the exhaust, and many other factors will make it so at different rpms, the engine will produce different levels of power.

Now lets look at two differently designed systems. A big truck meant for hauling, and a sports car.

When the engineers were presented with the task of producing a big truck engine, they figured that getting the darn truck moving, and climbing hills while hauling lots of mass was more important than speed. They produced an engine with lots of torque, but the design to produce that amount of torque, with that size engine, and within a certain budget, imposed limits on the maximum rpms of the engine. The engine produces a maximum of 400 ft-lbs of torque at 2000 rpms (152 HP), but redlines at 3000 rpms with a 200 ft-lbs of torque (114 HP), peaking HP somewhere around 2500 rpms where it has 345 ft-lbs of torque (164 HP).

Why did they need so much torque? Torque allows your engine to increase the rpms of the crank, which resists that increase due to forces such as friction, gravity, drag, inertia, whatever. Here they have a big heavy truck, that's a lot of change in inertia, or a lot of overcoming gravity (both of which depend on mass.) The big wheels produce more friction than a small set of tires, and not too many truck designes are overly concerend about their drag coeficient.

For the sports car engine they decided to go with setup with less torque, but one which could acheive much higher rpms. Although this little engine only had a maximum torque value of 150 ft-lbs at 3500 rpms (99 hp), the torque was still at 140 ft-lbs at 6200 rpms (165 hp), and didn't redline till 7000 rpms with 110 ft-lbs of torque (146 hp).

Why didn't they need as much torque for the sports car? Yes they could have used it, but with the budget, and engine size constraints, they couldn't do so. In order to build an engine with that much torque, they would have had to compromise other apsects of the sports-car's appeal, as the engine would weigh quite a lot, hurting balance and cornering, or be too expensive. The car had a low enough mass, that they figured the lower torque would be sufficient, and speeds could be achieved by the higher rpms allowing more work to be done.

Torque is a measurment of the power.
(Power)
A big 300 lb guy pushes you and you move back 4 feet.
A little 140 lb guy can only push you back 1 foot.

HP is a meaurment of the work.
(Work)
A big guy can push you 4 feet every 24 seconds. (truck)
A little guy can push you 1 foot every 6 seconds. (sports car)

Note: I'm still learning the terminology, and starting to understand the principles. Please point out holes in this post, but go easy on me smile.gif

 

yeah, you just kinda reiterated what has already been said. however, what makes the torque peak is the volumetric efficiency of the engine. i woulnd't necessarily say it's budget contraints that makes ford produce large displacement, torquey engines. it's reliability. almost every industrial engine, not necessarily being for a vehicle, that is a diesel is designed to run....and run....and run for a long time. and by the time the engine dies, it's more cost efficient to just buy a new engine. that's why they don't turn a lot of rpms or make a lot of hp, but they make enough torque to do whatever job they were designed to do...and for a REALLY long time. when an engine's volumetric efficiency goes up, it's reliablity/longevity goes down. formual 1 engines' volumetric efficiency is way up there. i wouldn't say it's 100%, but much more than ours are. our engines are probably around 50%. however, formula 1 engines (and all race engines) are designed to last for the duration of whatever race it's in. they plan on rebuilding it. it's just part of the deal. am i making sense, or just rambling?

 

[ January 13, 2003, 09:16 AM: Message edited by: Frostbyte ]

 

yeah, we are just kinda repeating what has been said, but in our own words. sorry. smile.gif i think your understanding of VE is what mine initally was. it's how efficiently the engine moves air. just because it's moving air better, this doesn't mean it's putting less stress on the engine. see what i'm saying? yeah, it moves air more efficiently, but it's putting a greater strain on the engine. umm, about more ford, or any manufacturer, putting more r&d into an engine design as the cost limiter, i disagree with you there. it's all about what the engine was designed to do, and how long it was designed to do it for. ford wants their trucks to tow 2,000 pounds for a long time. they don't sell their trucks to guys who want to race v10, turbo diesels. if you bought one of the kits you're talking about to raise the redline, you're not increasing the VE of the engine, you're just making it turn more rpms, which *may* result in more hp. but what if the VE drops so significantly, that raising the redline from 3500 to 5000 actually results in no more hp in that range? i guess what i've learned from this is that, like i said earlier, neither measurement is *better.* they are both useful in their own ways, and represent power, but in different manners.