The Great Torque vs. Horsepower Debate

[TheSt|G]

Originally Posted by phenom86

yeah its very technical but once you read and understand your question will be answered.. My ultimate question is why do we have a dip in our torque band, whats the cause of it and why is it there.

I suspect that may be when the engine switches over from port and direct injection to straight direct injection. Definitely will be something that gets answered eventually.

[BigFatFlip]

knowledge....om nom nom nom

[Dimman]

Originally Posted by phenom86

your right, ive seen on this forum is HP concern when we are introduced to new products. I dont want to have a too high HP car but a car thats truly balanced.. I'd like to get rid of the torque dip while im not running forced induction, if we can get rid of the dip with proper tune i'd be a happy man.

The dip issue will go back to your exhaust/wave tuning articles. Plus how wave tuning can interact between the exhaust and intake.

Given the torque output rpm and size of the motor, the reality is this is more of a double peak, than a dip. It may be possible to move some of the first low rpm peak to the high rpm range by screwing around with intake runner and exhaust runner sizing/lengths, but the result would be more of a ramp. Car would feel gut less down low, but pull much harder up top. Maybe more Honda-like.

[dem00n]

Its article likes these that make me wish more Colleges offered automotive engineering, though i guess i'll stick with Electrical Engineering.

[Coheed]

Horse power is all that matters. Where you make it and how much

[SUB-FT86]

I think it all depends on what you buy a sports car for. I dont find high rpm engine exciting unless I was a avid track goer. I prefer mid-high range excitement. I prefer a dual purpose engine. It makes it fun all the time.

[Captain Snooze]

Originally Posted by Coheed

power is all that matters. Where you make it and how much

Fixed.

[Coheed]

Originally Posted by Captain Snooze

Fixed.

It didn't need fixing, but both statements are equally true.

[Coheed]

Look at this graph. Three different theoretical HP curves.

Black- Tons of low end torque results is lots of low end HP, much more than the others.
Blue- Turbo surge in the mid range results in lots of midrange HP, more HP than black.
Green- Peaky NA engine. Makes more HP than black, but only on the high end.

Black will be faster than blue until the mid-range. And faster than green until the top end. Even though black doesn't have as much peak HP, it will be faster everywhere else in the powerband. However, if the other engines are kept within their peak HP limits, they will likely be faster.

HP is a product of torque, so comparing the two doesn't make sense. I do think there is a basis here on where TQ is made though. The question is: where do you want your peak torque? The best answer is: Everywhere. But when you can't get constant peak torque, you have to settle on where the engine spends most of its time, or its purpose. A high strung engine will need revs to be quick. A mid-range engine will want to be shifted early or else feel overly strained when struggling to hit high rpm.

Of course, these aren't new concepts to anyone here. But comparing HP to TQ directly is silly. Like comparing Volts to Watts, Density to volume etc.

[arghx7]

There's a lot of overthinking and TL;DR in this thread.

Power reflects whether torque is going up, going down, or staying the same over the rpm range. If torque is rising quickly as rpms go up, power will rise quickly. If torque is flat, horsepower will continue to increase. When torque starts dropping, power will flatten out and eventually drop. For those of you with some fuzzy understanding of calculus, think of the power curve as sort of like the 2nd derivative of the torque curve.

I am attaching a chart that shows the dyno (crank power) of the new M5 (solid line) with the twin turbo V8 and the old M5 with the high revving V10. Notice how on the new M5, when torque is flat the power increases steadily. When torque drops, the power flattens out and here falls at redline.



the graph above uses metric units of newton-meters (torque) and killowatts (power). When using standard/English units, torque (lb/ft) and horsepower always cross at 5252 rpm.

And don't bother saying whether a given engine will be faster or not faster, unless you have two engine dynos racing each other. In many cases there are too many variables with the transmission, driver, etc.

[White Shadow]

Lets be realistic here. For a street driven car, big torque is much more useful than big HP. Why? Simple--we spend little of our time at or near redline. Much more time is spent in the lower RPM range where torque is more important.

Personally, I have no interest in a car that has a low torque output and makes maximum HP way up in the rev range. That might be fun on a track, but not so much on the street.

[White Shadow]

Originally Posted by DarkSunrise

A high hp, low torque engine is fine if you have proper gearing and are willing to downshift.

And if you're willing to keep the RPMs in the stratosphere all the time, or at least any time you want any kind of decent acceleration.

[soros151]

Glad to see others enjoy automotive physics as I do. Loving this thread! 1+ for it!

[brewksy]

This thread bothers me... not sure why. Let me clarify that the OP doesn't bother me at all, just the discussion that typically follows such an article. Maybe it's because all of the technical jargon about horsepower and torque doesn't really explain the subjective, only allows us to ruminate on graphs and charts and what it means to the human experience.

The nature of a car is derived from driving it, shifting it, and experiencing it. Choosing how to coax power from an engine is dependent on the entire drivetrain - engine, transmission, steering, pedal (feel, range of motion), etc. However, using a horsepower/torque curve as a measure of experience? A dyno plot graph looks at one gear. An entire gear from some small number like 1000 RPM up to some large number like 9000 RPM. Do we drive like this? Do we experience a car's character by doing such an exercise? I would say no.

I think of when my wife drives the STI - she never goes above 4500 RPM, even if she's trying to accelerate hard. She considers the STI to be rather sluggish (laggy), especially in comparison to our supercharged RL. I find the opposite to be true as I have no fear revving the engine to near-redline numbers.

Here's a couple videos:
[ame="http://www.youtube.com/watch?v=5yKb6iSWc0k&feature=fvst"]2012 Corvette ZR1 Takes on Nurburgring - YouTube[/ame]
[ame="http://www.youtube.com/watch?v=R2EQjPpZum4&feature=relmfu"]Ferrari 360 Challenge Ed Zabinski Lap10 Traqmate GPS Data Acquisition - YouTube[/ame]
[ame="http://www.youtube.com/watch?v=Po4yoytAdDg"]AiM Solo DL and SmartyCam in a 458 Italia at VIR - YouTube[/ame]
[ame="http://www.youtube.com/watch?v=tz_JZKpqmg4"]1:27.59 Lap -- Getting Quicker at Willow Springs - YouTube[/ame]

All of those show RPMs on the screen as people are driving around various tracks. Some go below 4K in corners on some tracks, while others stay much higher in the RPM range. But it depends on the track, the person, the car... none of these variables are the same on any different day. I just don't see how arguing the technicalities of HP/Torque as making the discussion about what's "best" any more relevant.

YMMV, IMO, etc.