Why is it that they seem to always be the same ? Jay's post has 2 engines with completely different builds and cubic inches are the same at 5250 rpm and noticed this on Barrys builds to and im just wondering why it is. Is it the same on all V8s ? What about straight 6s and 4s, Are they the same as V8s or dose the HP&TQ cross at a different RPMs on them ?

Since we measure torque and calculate horspower from that measurement - the two MUST cross at 5250 RPM to be legitimate. If you ever see a dyno chart that does not cross at that point you should consider it highly suspect - unless dealing with an engine that power peaks below the 5250 mark.

Yes that is because hp is a product of tq. I'm not good with putting it into words and it took me a while to comprehend it but basically without tq you don't have hp.

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torque is a engine ability to move a given weight .... horse power is how fast a engine can move the given weight

example .... a 600 HP , 370 FT lbs torque small block chrevy will out accelerate a BB chrevy 454 with 270 horse power and 480 ft lbs of torque .... but the 480 ft lbs of torque BB 454 will tow a trailer way better than the 600 HP small block ... IMHO anyway

The force is measured at the tire, not at the back of the engine (so it is not the raw torque of the engine). The torque multiplication of the drivetrain (including the diameter of the tires) must be factored to determine force.

At any given RPM, increasing the torque is the same as increasing the power output.

This message has been edited by Halowe on Nov 12, 2012 7:36 AM This message has been edited by Halowe on Nov 12, 2012 7:27 AM

To add to what has already been said, or to say it a different way, Horsepower is a function of Torque, where function is a mathematical equation that relates an input to an output. Expressed as f(x) and stated as "f of x".

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5252 is where the lines will ALWAYS cross, no exceptions and the reason is simply because of the way horsepower is figured using torque times rpm divided by 5252 which is the constant used to calculate horsepower. Since you're dividing by that number both horsepower and torque have to be the same at 5252rpm that's just the way math works.

If you got even a 2 stoke detroit that high it would be a measure of the torque..

November 12 2012, 9:08 AM

as it exploded like a 1/2 ton chunk of iron :-)If you back into it, the Detroit can make 800 lbs ft of torque at 2000 rpms, but only 210 hp at that rpm, but flat line zero at 5250 if it cant get there, mathematically it could be making 15 hp calculated backwards to a torque value, but I don't even believe that value would turn the engine.

For example, I can put out about 1000ftlb with my arm, given a long enough pipe, and easily move a big 4x4 with it. But I wont turn a very good e.t. that way. You'd need a calendar. Horsepower wins, not torque.

The reason folks THINK torque matters is that it reflects horsepower-at-low-rpm, which matters quite a bit, usually more than peak horsepower.

I have a 2012 Ford Super Duty brochure in front of me, and they show a dyno graph for the 6.7L Powerstroke diesel. It shows peak torque of 800 ft/lbs at about 1500 RPM, and peak HP of 400 around 3700 RPM. Both lines drop off sharply at about 3000 RPM , and appear to be ready to cross over at about 3600 RPM. The way the graph lines drop off so quickly, it would appear if the engine could get anywhere near 5252 RPM, the numbers would be under 50HP & ft/lbs of torque.

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So on the far opposite end of the scale, say a decade old Formula One engine that goes to 20,000 RPM and probably idles at 5250 it probably is only starting it's torque curve at that speed and obviously horsepower hasn't peaked either so where do those cross or is this a repeating scale and that falls at 10,500 (double the 5250)?

If a very low RPM or ultra high RPM engine makes no power or torque at 5250 i'm curious how HP can be calculated off that if torque at that speed is non-existant.

Zero torque = Zero horsepower, no matter what the engine speed is. So if the engine won't run at 5252 RPM, it is delivering zero torque and horsepower. If the engine is running though, it is unlikely that it is delivering zero torque. You could stop the flywheel with a feather if that were the case. And if the engine is delivering only 1 lb-ft of torque at 5252 RPM, then it is also delivering 1 horsepower at that speed.

Horsepower is the rate of producing torque, so the two quatities are functions
are directly related to each other:

HP = (TQ*2.0*PI*RPM)/33000.0
TQ = (33000.0*HP)/(2.0*PI*RPM)

where:

TQ = torque in ft-lbs
HP = power in horsepower
RPM = engine speed in revolutions per minute
PI = the mathematical constant PI (approximately 3.141592654)
Note: 33000 = conversion factor (550 ft-lbs/sec * 60 sec/min)

In general, the torque and power peaks do not occur simultaneously (i.e. they
occur at different rpm's). However, since the curves are functions of each
other, the curves will always cross at 5252 RPM when the units are torque in
ft-lb and power in Horsepower. There's nothing magic about that number and it
will have a different value for different units. If you assume power in Watts
and torque in Newton-meters, you'll get a different cross-over RPM.

Torque is the rotary equivalent of force and is what accelerates a vehicle but
it's the torque at the rear wheels that accelerates the vehicle, not the torque
at the crankshaft. However, horsepower (at the crankshaft) is the measure of
how much RPM can be traded for rear wheel torque via gearing. Gearing is the
reason you accelerate harder in 1st gear than you do in 4th or 5th (there's
also an aerodynamic drag effect)

for answering my question everybody. I didn't think it would get this many responces to the question when i asked. Still seems kind of wild that engines have the same HP&TQ at 5250 rpm no matter the build. Thank you everyone for responding.