Damn those k20's
12-16-2006, 05:39 PM
#61
TECH Senior Member
Originally Posted by 25psi
PLEASE REREAD! PLEASE REREAD! PLEASE REREAD! PLEASE REREAD! PLEASE REREAD! PLEASE REREAD! PLEASE REREAD! PLEASE REREAD!
Take an extreme example to illustrate why the torque number is meaningless. Compare in the same car with two different engines, an engine that puts out 50 ft lbs of torque and an engine that puts out 500 ft lbs. Say we are going to race the cars for a given distance with a 1 speed transmission. Which engine will be faster?
Hmmm, can't say right?
Lets say the 50 ft lb engine puts out it's 50 ft lbs to 10000 RPM, and the 500 ft lb engine puts out it's 500 ft lbs to 1000 RPM. Now we are getting somewhere, because before, with out knowing the speeds at which the engines produce those numbers, we don't know how much power they can produce, which tells what gearing they can support in the race to distance without hitting redline.
Now, for the 50 ft lb engine we put in 20:1 rear gears and when we run it on our racetrack we just get to 10,000 RPM right at the finish line. Everything looks good; the gears maximize the potential of the car as it sits for this combination.
Now we put in our 500 ft lb engine, and leave the gears the same. Now the engine redlines about a tenth of the way down the track, the 20:1 rear is no good. We look at the first combination and we know to go the same speed with 1/10 the redline we need 1/10 the gears, right? So replace the 20:1 rear with a 2:1 rear. Now the car will run the same, because both cars have the same HP (RPM x T)/2525 in both cases. They also have the same torque at the rear wheels (50 x 20= 500 x 2). So what number told the tale, the torque numbers, which varied by a factor of 10, or the HP number, which is the same?
In order to not have to calculate rear wheel torque every time you want to compare two cars, or even the same car, you can just look at the calculated HP number. The HP number tells the whole story.
Take an extreme example to illustrate why the torque number is meaningless. Compare in the same car with two different engines, an engine that puts out 50 ft lbs of torque and an engine that puts out 500 ft lbs. Say we are going to race the cars for a given distance with a 1 speed transmission. Which engine will be faster?
Hmmm, can't say right?
Lets say the 50 ft lb engine puts out it's 50 ft lbs to 10000 RPM, and the 500 ft lb engine puts out it's 500 ft lbs to 1000 RPM. Now we are getting somewhere, because before, with out knowing the speeds at which the engines produce those numbers, we don't know how much power they can produce, which tells what gearing they can support in the race to distance without hitting redline.
Now, for the 50 ft lb engine we put in 20:1 rear gears and when we run it on our racetrack we just get to 10,000 RPM right at the finish line. Everything looks good; the gears maximize the potential of the car as it sits for this combination.
Now we put in our 500 ft lb engine, and leave the gears the same. Now the engine redlines about a tenth of the way down the track, the 20:1 rear is no good. We look at the first combination and we know to go the same speed with 1/10 the redline we need 1/10 the gears, right? So replace the 20:1 rear with a 2:1 rear. Now the car will run the same, because both cars have the same HP (RPM x T)/2525 in both cases. They also have the same torque at the rear wheels (50 x 20= 500 x 2). So what number told the tale, the torque numbers, which varied by a factor of 10, or the HP number, which is the same?
In order to not have to calculate rear wheel torque every time you want to compare two cars, or even the same car, you can just look at the calculated HP number. The HP number tells the whole story.
12-16-2006, 05:41 PM
#62
TECH Senior Member
Originally Posted by 25psi
Who cares how power is achieved! Different cars have different power curves. It doesnt mean that one is better than the other.
Since you seem to mock a supras torque curve, but what has taken as ls1 so long to run 6.4's at 220mph? Despite having twice the liters and a two more cylinders, one would think a supra with such a peak torque curve would have a hard time running those number eh!
So why did it take the Supra so long compared to the LS1 to run 6.4s?
Whats next, you want to tell me hp/l is important???
So now, answer, which car will be quicker, A or B, given both have the same gearing, weight, etc. etc.
12-16-2006, 05:49 PM
#63
TECH Senior Member
Originally Posted by koolkoreanked
actually my car is n/a. The car pulls hardest when I mash the pedal at 6 grand or higher when the hp is highest and flatest. When I do a low rpm roll where tq is highest I usually get pulled on by about a fender if I'm racing a bolt-on ls1. Its not until 6k where I actually pull that fender back and pass whatever it is I'm racing. What you fail to understand or didn't mention is that there is too ways to make power... High tq low rpm motors... Or low tq high rpm motors like mine. Tho I make all my tq down low its not until the motor is spinning do I actually start pulling hard.
And theres only 1 way to "make power" thats torque X RPM /5252.
