Why does torque always drop off at 5200 RPM and Horsepower begins taking over. Check out the dyno sheets.

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HP is calculated from torque... the formula is

HP = torque x RPM / (33000/2pi)

33000/2pi = approx. 5252.11 IIRC

You may recall from physics that

1 HP = 33000 lbs 1 ft. in 1 min.,
or
1 HP = 33000ft-lbs/min

To equate rotational torque to linear force you need the 2pi factor.

So:

HP = torque (RPM ÷ 5252), the factor in parentheses has the value of unity at 5252 RPM; below that the numerical value of HP by definition is less than the numerical value of torque, and above it at RPMs greater than 5252

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Torque doesn't always "drop off" at 5252 either, but they will always cross there.

 

Correct. Torque and HP cross at 5252 because of the formula to calculate HP from torque. Torque usually starts to drop off just after that just because of the amount of rpms the engine is turning. It can remain flat but doesn't climb much more.

Torque is produced by the brute strength on the engine at low rpms. At higher rpms it doesn't take as much force so torque is less.

HP on the other hand starts low in the rpms then rises as the rpms increase. After crossing the torque curve at 5252 HP can still increase (depending on the engine combo). Since HP is defined as the amount of work being done, HP increases after 5252 because it takes less effort to produce the same amount of work because the torque force is less. There's always a limit to the amount of torque and HP that an engine can produce. It just depends on what parts are used in the engine. An engine that produces a peak of 300 HP at 5000 rpm will then start to drop off and have less HP at 5252. Another engine that produces 500 HP at 6500 rpm will also have a lot more torque because at 5252 it will probably be putting out 400+HP at 5252.

The more torque you make at higher rpms, the more HP you have. Making a street engine that makes peak torque at 5000 is a poor combination since a street engine rairly gets over 3500 rpm.

 

Correct, most of the time. On some serious engines, the torque curve and HP curves are still plotting positively (increasing) at that RPM, so many times the torque and HP curves track along each other for several hundred RPM or more. Wouldn't that be cool?

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Vader
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Since HP is defined as the amount of work being done, HP increases after 5252 because it takes less effort to produce the same amount of work because the torque force is less

All very good answers... but can someone give more explaination on the above. I mean I understand the formula.

Using the above as an example.. if the torque was much higher than the HP... then at 5252... would the torque continue to stay above? Same goes with a car that has alot of horsepower but very low amount of torque... could the HP lead the whole time?

But going by the equation above... I'd say it'd probably be impossible since torque leads to HP.

------------------
91 Z28
Best Time Slip:
60' - 2.098
1/8 - 9.137 , MPH - 76.21
1/4 - 14.213, MPH - 97.55
Performace Mods: B&B Exhaust, few free mods.
Appearance Mods: SS wheels, 2.5" Cowl Hood... New 100% Black paint job, Clear Side Marker Lights
Stereo: Alpine 855, Infinity Kappas all around, Infinity 150x2 amp (POS), Infinity Perfect 10 in hatch.
Pictures at Here
ICQ: 1437212
AOL: normalmatt9