I understand both of these separately, however when I read specs how does one tell what is the best ratio between torque and horsepower? Many car companies say, " they have the best torque to HP ratio," but what is really the best ratio? I drive a Miata Mazdaspeed, an F-150 and Subaru Forester.
Thank you
The F150 is used to carry heavy loads and towing trailers. It should have a good torque to HP ratio. On the others, it does’nt matter since all you have to do is push the pedal down and get into a lower gear to get more oomph.
Torque give acceleration and horse power gives top speed. Torque = HP @ 5,250 rpm.
Some people like to get specific about engines. I like to know how the transmission performs. Sometimes you have to drive it because the numbers don’t really matter much. The false information ratio is very high at times. There’s one of you and thousands of irrelevant facts.
@twotone described it nicely. If you like jack rabbit starts, good 0-30 times, high torque will serve you well. If you want to go fast for miles at a time, 70-100 mph say, up and down hills, horsepower wins.
Engine designers must have rules of thumb on the compromises involved for gasoline engines, involving the total displacement, number of cylinders, compression ratio, etc.
Electric engine cars provide a whole different set of hp/torque/rpm compromises; they have considerably more torque at lower rpms. That’s why when you see a Tesla Model S take off from the stop light, you won’t be seeing it for long. They are super zippy from 0-30.
And as @pleasedodgevan2 says, trying to decide based on engine specs isn’t the best way to go. A test drive tells you what you want to know about HP/torque/and rpms for a car much better than a spec sheet.
As far as torque and horsepower, acceleration and top speed is concerned, they are not exclusive of eachother. A high torque motor with lots of internal mass may not wind up as quickly and not generate enough horse power to accelerate as fast as a motor with less torque. Diesels are an example of this as well as some high torque, lower hp truck gas motors. To accelerate well, you need both torque and adequate horsepower. To travel at high speed, you still need adaquate torque as well, in additional to the horse power.
The unmentioned factor in all of this when talking about torque and horse power and acceleration and top speed, is the transmission. If the ratios are not matched and the transmission does not respond appropriately if it’s an auto, the best motor in the world can be a dog. So, just looking at a motors ratings does not tell the entire story…and then there is the traction in the drive train. A fwd 300 hp compact can have all the torque in the world and it won’t out accelerate a balanced rwd car of the same weight with FEWER hp and LESS torque. That’s where Awd comes in when accelerating in light cars with powerful motors.
Electric motors make the ICE measurements obsolete. They are in a world of their own because their inherent efficiency. Electric motors do not necessarily have more torque at any particular rpm then an ice motor. They just have all their rated torque throughout most of their rpm range, from 0 to what ever. So, even an electric motor with 250 ft lbs of torque can out accelerate a gas motor with 300 plus in the same car. That 250 is available ALL OF THE TIME.
The only time torque and horsepower ratings mattered to me was when I bought a used '65 Pontiac 2+2. It had the monster 3 deuce 421 engine under the hood. I was told that the torque was about 475 ft pounds and the engine a mere 375 horse.
All of that power and the car still looked like something your grandmother would drive. Still…I held the record for the longest patch of burnt rubber in our little town for about 2 years. I did have an advantage since the tires were only 7 inches wide back then.
Some dude with a 427 Cobra passed up my fading dark line on the asphalt and just kept going. I have a feeling his torque and horsepower specs were a lot higher than mine.
No such thing as a ‘best’ ratio. And with turbos like your Mazda it’s even harder to interpret just the peak values. The output is controlled by the computer to stay within limits. That now applies to lots of cars now that turbos of more common.
Horsepower is a combination of torque and RPM. For pulling a lot of weight, lots of torque is nice because it gives you adequate horsepower at an reasonable RPM. 450 lb. ft. of torque at 2,500 RPM will give you about 215 HP. 215 HP will do a lot! The 30,000 lb. school bus I drive only has 240 HP and it gets around. It is just a matter of having the power you need without having to run at a screaming RPM. A diesel that can put out 140 HP at 2,500 RPM will tow a camper better than a small gasoline engine that puts out the same HP at 6,500 RPM.
It’s interesting to note, that tractors, which you would think need lots of torque for their output, have motors whose ratings are mostly horsepower rated only. Why ? Because the transmission, especially the hydrostatic generates the torque as a result of hydraulic pressure, dependent more on how fast the motor spins the pump then how much torque it actually delivers itself. And, as @douleclutch says, they are not mutually exclusive regardless. Tractor motors are an example of the fallacy that all diesel motors have gobs of torque. They have gobs of efficiency operating in a limited range and and generating enough torque to do the job by way of it’s transmission. The transmission is the heart of most tractors as we know them, not the motor. Pretty much the same with buses too…the tranny is the key. A gas motor can run a truck for towing, a bus, a tractor or everything else as well as any diesel given the right transmission. It just doesn’t operate as efficiently, reliably and needs much more maintenance over the same life time.
The shape of the torque vs speed graph is more important to drivability than the peak torque, which is the published number.
A torque curve that is nearly flat over a wide range of speeds offers more flexibility.
Electric motors are the ultimate because their torque curve is essentially ruler flat down to near-zero speed.
A single speed transmission is often all that’s needed.
@circuitsmith. Right, you need a flat torque curve for towing and lugging. The higher the better. Diesels have a flatter curve than highly tuned gas engines. Truck drivers don’t want to be shifting contnuously.
Modern gasoline car engines with fairly high specific outputs will typically produce over 90% of thier maximum torque from slightly below 2,000 RPM all the way to red line. Diesels in big trucks usually start to pull real hard around 1,200 RPM, and thier maximum HP is usually somewhere between 1,800 and 1,900 RPM. A 500 HP car engine might develop 500 HP by producing about 437 lb. ft. pf torque @ 6,000 RPM, while an over-the-road truck engine like a Cummins N14 or a Caterpillar C15 might develop 500 HP by producing about 1,420 lb. ft. of torque @ 1,850 RPM. One is good for making a 3,200 lb. Corvette go like heck, the other is good for dragging 80,000 lbs. all over North America 10 hours a day. On -road diesels usually have a greater percentage of thier HP in a more usable RPM range. This also applies to little VW Jetta TDI engines as well. A Jetta Diesel may only have about 140 maximum HP, but at 2000-2500 RPM, it will match a good size V-6 gasoline engine at the same RPM.
There is no optimum torque vs horsepower range. Or curve. Espacially since you didn;t tell us the criteria; 0-60 acceleration, 60-100 accelertion, or gas mileage. The bottom line is that these are just ways to measure the ability to do work and to measure twisting force throughout the operating range of the engine. That’s all they are.
A Lotus has much less of both that most cars, but it’ll also suck the headlights out of most from 0-60. It’s gear ratios, small cross-section (aerodynamically), and feather-light weight allow it to do that.
The bottom line is, does it feel to your bottom the way you want it to when you’re driving it the way you want to? If not, my suggestions would be to either find a reputable speed shop and discuss with them what they can do for you within your budgetary constraints. Don’t get hung up on the numbers.
Yes, the numbers are there to confuse the public. Consider that an old 75 horse power John Deere Diesel required either a 24 volt starter powered by 4 large 6 volt batteries or an attached 4 cylinder gasoline engine to get it started. Maybe there should be a Kentucky Derby horsepower and a Budweiser Clydesdale horsepower.
For those unfamiliar with a tractor pull this tractor is at wide open throttle in 1st gear pulling a sled that has several tons of weight being incrementally added. If you follow the entire video the last words from the announcer are “this is our first full pull of the day.” The tractor is a John Deere 830 diesel.
That’s one heck of a ripplewall.
Your best truck diesels have high torque rise an engine with high torque rise,will eat an older high HP diesel with low torque rise for lunch no matter what the gearbox until you get the high hp engine on the road -then you can cruise.I noticed this in Charlottesville at stop lights,when the Mack ,I was driving would pull away from the frantic gear jammers-but when they caught thier breath watch out(I would sooner shift 5 in town then having to row 18)-Kevin