Forester 2.5xt or Tucson premium crdi

[niky]

Sorry, let me elaborate. I got to my conclusion when i saw the formula POWER=TORQUE X CONSTANT X RPM / CONSTANT on Wiki. Assuming it's true, it means Power is a function of Torque and RPM -- meaning it's an all-encompassing figure given current RPM levels.

On the other hand, some people may consider high Torque cars and think they accelerate faster despite lower RPM (I think electric is the ultimate example of this). Not true.

In that sense, HP is a better indication of acceleration because it already includes both torque AND RPM. OTH, having higher torque will always mean having stronger PULLING power but not necessarily accelerate faster.

If this is what Niky means, and I think it is, it, might be too technical for most people who might still think torque is the all-important number for acceleration.

If the formula is incorrect, I stand corrected and I apologize for Wiki ...

Sorry... didn't see this reply!

Sobrang overdue... but it's even more complicated than that.

More torque at a given rpm always equals better acceleration. This is always true. Which is why turbodiesels pull so hard just off idle.

But torque is multiplied through the gears. The lower the gear, the higher the torque. That's why even a Kia Picanto can do a burnout in first gear.

So, your turbodiesel jumps off the line because it has a few hundred ft-lbs of torque... multiplied by first gear = a gazillion ft-lbs of torque.

The turbo-gasoline engine doesn't have a chance, it gets left behind at the starting line.

But something funny happens when the turbodiesel gets to 4000 rpm. It has to shift.

The gasoline engine is just getting started. It makes the same torque at 4000-5000 rpm. As the turbodiesel shifts into 2nd gear, which has a lower multiplication factor, the gasoline engine stays in first and zips away.

This is why you want horsepower at higher revs rather than torque at lower revs for racing. High horsepower at high revs allows you to stay in gear longer, and maximize the multiplication factor of the gear. So in, essence, you're right.

That's why SiRs are so sucky in traffic, but so good in drag races. In a drag race, an SiR can stay in first gear till 8000 rpm (9000+ with mods), while other cars have to shift into second much earlier.

But in the real-world, since you're stuck between 2000-4000 rpm most of the time, torque is king. But more importantly, it's how much torque you have over the whole rpm band. Not just peak. That's why the Navara isn't any quicker than a Ford Ranger. It has higher peak torque, but it has a narrow torque band, so you have to keep shifting, while the Ford Ranger's meaty powerband allows it to stay in gear longer.

This is where average horsepower comes in. Knowing the average horsepower of an engine over a range of rpms will tell you more about performance than peak horsepower, but manufacturers don't tend to publish this. However, US motor-building competitions do. They rightfully regard average horsepower as the more important number to build for when building a competition engine.

But even with such handicaps, gearing and drive-ratios can really make a difference. The new 370Z is much faster than the old 350Z in a drag-race, even with less torque and a puny 30 hp advantage, thanks to a shorter final-drive ratio.

Complicated, no? :hysterical:

In essence, performance is best predicted by average horsepower and gearing, all else being equal.