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Why do torque and hp always cross at 5250 rpm?

23K views 26 replies 10 participants last post by  drenbircs 
#1 ·
I think I've only seen 1 dyno chart that that wasn't true. (it was less that 5000).

Is it different for 4 cyl engines?

Just curious on the theory....

:patriot:
 
#8 ·
disagree , my motor redlines at 6500 rpm , produces 501 hp @6200rpm ,are you really suggesting the best shift point for best times is 5200rpm? ever ?
What really accellerates the car? Torque or HP ?

Read this: http://www.elephantracing.com/techtopic/hpvstorque.htm

They suggest both are a factor, but only if you consider "Torque Multiplication"

Read the section of Torque Multiplication. Then consider his example that is a race car - 2nd is 1:1 whereas in a Vette, 4th is 1:1.

I'm sure it varies car to car as well. Mine loses power at 5500rpm and I find the 5200 to 5500 range doesn't do much - I stop accelerating.
 
#3 ·
my guess is engine design it alot of weight to be throwing around that fast
 
#14 ·
Basically, I believe torque is the measure of amount of work/force, and horsepower is the measure of how fast the work/force can be performed/applied.
 
#18 ·
Because the mathematical definition of Horsepower as it partains to torque is:
Horsepower = (Torque X RPM) / 5252

Therefore Horsepower must ALWAYS equal torque at 5252RPM, universally, regardless of what engine is being dynoed.

If it doesn't, you either have different scales for torque and hp, or you have a false chart ;)

For those wanting a more in-depth explanation, here is a reasonably good one:
http://www.revsearch.com/dynamometer/torque_vs_horsepower.html
 
#22 ·
For myself I usually think in this way:
You have a scaffold plank pivot on a drum.
Put the drum close to one side i.e the short side and think of it as the rear axel and the long side of the plank the engine side.
1.Use power on long side to lift a known weight.
Shift the pivot [drum] more to centre
2.Use same power on long side to lift same known weight [same power but a little less torque]
3.Then put drum which is the pivvot point in the centre and use same power to lift the same known weight on the other side. Then power=torque
Looking at number 1, same power but much more torque? Number 2. same power less torque and 3. power equals torque.
 
#23 ·
This is an interesting discussion - old post I know. And HP vs Torque has always been confusing - but Torque is the power, HP is a derivative of torque and does not exist without it. Put simply, the longer you can maintain your torque curve past 5250 RPM, the bigger your HP number will be. Why this is a good thing is because you can keep it in the lower gear longer (for better acceleration) before you need to change up. So as long as you know at what revs the torque starts to nosedive, it matters not what the HP figure is.
 
#24 ·
torque is good
 
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