HP is a measure of work produced by an engine (= to 746 watts/HP). Torque is a measure of the rotational force of the crankshaft. If this is true than horsepower is more or less meaningless as the torque is ultimately what determines how fast the driveline rotates/accelerates. OK, I over simplified it, but HP and torque are not perfectly linear. Adding HP does not always result in increased torque (though there is often a corresponding gain in torque with an upward shift in the curve). So, if one is increasing horsepower you should be sure that torque is increasing also, correct? Also, for street driven cars, should one build for maximum torque as opposed to HP? Which one would be faster on the street? 400 HP with 300 lb ft of torque or 300 HP with 400 lb ft of torque? Finally, should the tranmission shift just after peak HP or peak torque? I vote for peak torque on the street.
More HP is always going to be faster. More torque will usually feel quicker. Think about the land-speed guys...They usually have a lot of horsepower, but the gearing that they run doesn't allow them to have much torque. Stoplight to stoplight, most cars from this board would be able to beat them, but at the end of their flying mile, we wouldn't stand a chance. That's why they need so much room. Torque is definitely king on most streets. Hope I didn't confuse you more. Later,
I've always wondered about the same type question. You have 2 cars that weight the same, one is set-up with a 302 with alot of HP and a 4.10 gear to get him moving. The other car is a 302 set-up for massive torque but with a 3.0 gear. The car with the 4.10 does'nt have as much torque so he needs the higher ratio gears to get him moving but the high torque engine is running a lower ratio gear because it has plenty to torque to get it moving. Which one will win in the 1/8th what about the 1/4? I remember riding with my dad in the tractor trailer. Once we were on the W. Virginia turnpike bob-tailing. Coming out of a toll booth I was ribbing my dad about being so slow and the car beside us, a camero beating us out of the last toll booth and basically cutting us off before the right lane ended. Using the torque of the diesel and using the 13 speed road ranger like a 4 speed he took off faster than most cars could. Really pinned me back in the seat. The guy in the camero had to drop back and fall in behind us very unhappily I might add. lol The torque of that impressed me clint
But, ultimately the HP is converted to rotating force, correct? Therefore, torque is still the force that turns the crank. More HP creates more work which "pushes" on the piston more creating greater downward force. But, I would think in some cases work/HP can be lost as heat and thus have little impact on the rotational force. I have wondered about this for years just thought I would throw this out there and see what others thought! Maxx, what type of torque are the land speed guys making at higher speeds. Maybe their torque curve is higher and the torque multiplication (gear ratios) are designed to harness torque at higher speeds. However, we agree that generally torque is king on the streets. This being the case, one should build a street engine for torque not HP, correct.
And hence to answer this age old question, stop light races and drag strips evolved. I think there's a little bit of a false premise here. I was just thinking about this a couple days ago. Setting up a 302 for "massive" torque vs high hp. I don't think you can get "massive" torque without some massive hp also. I didn't research it though so anyone feel free to correct me, but setting up for torque INSTEAD of hp would be kind of limiting I think(to both). Going for velocity would limit intake and carb sizes, and then you'd want a lower duration cam with lots of lift, which again is going to limit hp. Making a fun street motor with really good torque, probably fun at street lights but good at getting beat at a 1/4 strip. But massive torque? I don't know. I'm a bike guy so I always get back to bikes eventually, Harley's are supposed to have "massive" torgue, and they do have good torque, but my FJ with 165 rwhp out torques all of them, by a lot, even when their motor is much bigger. My curve is a lot higher though. So, IMHO, I'll take the high hp motor in your example with a high stall converter to go with it and it will still probably have higher torque too, just higher up. I'm going for 400 hp/400lbs(crank) torque in my motor. What is massive torque in your example? And real world, what goes down the strip faster is higher rpms and higher hp. But everyone has to decide on what they want to be driving around all the time. What I consider a good balance is a little higher up the hp/torque curve than a lot of people. I think all the talk about massive torque from a low hp motor has been ingrained from manufacturers advertising about motors that are specifically tuned for low rpm torque. "It will pull 4 stumps at a time!!!" Made to get a heavy vehicle moving easily, not win races. They don't ever mention how much hp (and possibly actual torque) they sacrificed to drop the torque curve way down low in the rpms. And a lot of this discussion is really about where the torque curve is instead of what the top number actually is.
Torque will define accelleration. As a car picks up speed, more power (HP) is needed to keep it at the speed, and to accellerate further will need even more power. So HP will define your top speed (in combination with maximum revs and gears), torque will define how fast you will get to that top speed.Torque is a measure of force excerted. HP is a measure of energy available.
They go together. Can't have one without the other, so they can't be treated as wholely seperate things. But yeah, I think of torque as acceleration and hp as top speed, realizing it really ain't that simple. And I therefore always want both.
I was trying to make a comparrison and did'nt really have a torque limit in mind. Did't do a very good job of it either. lol I guess you can't really seperate the two though. Is'nt it at 5250 RPM"S that torque and HP are the same? Or is that something else I'm thinking of? I'm sure the best engine would be the one with the most torque and HP. What I am trying to get across I can explain the easiest with my truck as an example, maybe. When I have the 3.70 gears in the truck and I am just cruising around it leaves from a dead stop easily but picks up speed slowy compared to when I have the 3.25 gears in it. With the 3.25 gears it seems like the engine is working at the same level but I am going faster for the same rpm's. I feel like the truck is faster with the 3.25 gears in it since for the same rpm's I'm moving faster. I know it is faster with the 3.70 gear or at least it should be. Sorry for writing books and explaining myself poorly. My back is really killing me this mornin and it's raining. I just can't make myself go out back and get to work. clint
I see what you are saying and see where I have faster and quicker mixed up. I know the truck is quicker with the 3.70 gears in it but in normal driving it FEELS quicker with the 3.25 gears in it due to the 3.25 gears giving me more speed for the same RPM's as the 3.70. So in normal driving just easing into the gas the engine has to turn faster to do the same speed with the higher ratio versus the lower ratio. But then when you floor it those 3.70's start to really shine don't they? lol clint
just to help confuse....er....expand the thought. its not just wether its torque or horsepower, but when. a tow vehicle will normally make all of its torque and power at lower rpm, my 390 is only good until about 4500 rpm but will tow my boat and camper and doesnt really act like there is any weight when accelereating off the line. an engine making as much torque and power later would notice it greatly off the line and on hills. another example of this is why my bronco with aod had worse gas mileage at a lower rpm than a similar one with the c-6. the engine wasnt re cammed to produce the power and torque at the lower rpm and had to struggle more to stay there at speed. more power is always good but how your going to use it is how you want to build. my truck will beat up on new dodge and chevy trucks, but it wouldnt stand up for more than a few yards against a vette or viper. (thats when the grabber comes in). I think maverick rick touches on this with bikes.
You can get real technical, and you can apply the terms to so many different things. When it comes to cars, all you have to know is: Torque is how much power, or strength an engine can make. Horsepower is how fast it can make that power. That is why a diesel can be rated at only 200 hp with 500 ft/lb torque. It is VERY strong, but cannot use that strength quickly... Therefore it can tow, but won't win any drag races. On the other side, you might see a riceburner brag about having 200 hp... But if torque is low, the car is not really strong, it just uses what it has rather quickly. That is what you must do with a smaller engine though. Even with a small block Ford, you must not get too overly focused on torque. An SBF will never be a torque monster, so you must have some revs to use what you got quickly.
i somewhat disagree with ratio411. horsepower is how much it can pull forward. torque is how much pressure at the crank pushing down. kinda blurs the lines. the equation above is a generalization, but is a decent rule of thumb. a small four cylinder doesnt normally have the off the line power because it is set up to make its power at higher rpms usually 4-10k it makes torque there as well. a big block makes it all at really low rpm and runs out before 6-7 grand at best. i know you can move the power band up and down the rpm range and get similar torque and horsepower to an extent. you are more likely to get more torque with bigger pistons or more of them (100 pound guy standing on a bar vs 350 pound guy standing on a bar vs three 100 pound guys standing on a bar). overall speed is a combination of horsepower and torque and when they are produced. sorry if this is really confusing. I would just stick with getting the torque and power based on how you plan to drive and what parts are on the market to get the most out of that, (unless you are an engineer for an engine/part manufacturer).
Rick Book, I think I'll go with your idea. It is simple! And as a general rule it is probably reasonable. So, for the average street car building for torque may be more "fun". Rick, can I offer one modification? HP=top speed Torque=acceleration
