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9,494 Posts

Am I just that stupid or am I missing something?

I can see maybe it revs faster with 4.30's but I'm totally lost now.

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Joined

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9,494 Posts

Am I just that stupid or am I missing something?

I can see maybe it revs faster with 4.30's but I'm totally lost now.

Joined

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14,484 Posts

Joined

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9,494 Posts

We were talking about hp so I'm right but in away we are both right and wrong. Ok if hp is the result of torque/rpm and the torque would change why doesn't the HP change? Anyone got any dyno sheets?

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14,484 Posts

The development of the steam engine provided a reason to compare the output of horses with that of the engines that could replace them. In 1702, Thomas Savery wrote in The Miner's Friend: "So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same. Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work…" The idea was later used by James Watt to help market his improved steam engine. He had previously agreed to take royalties of one third of the savings in coal from the older Newcomen steam engines.[3] This royalty scheme did not work with customers who did not have existing steam engines but used horses instead. Watt determined that a horse could turn a mill wheel 144 times in an hour (or 2.4 times a minute). The wheel was 12 feet in radius, therefore the horse travelled 2.4 × 2π × 12 feet in one minute. Watt judged that the horse could pull with a force of 180 pounds. So:

Others[

Most observers familiar with horses and their capabilities estimate that Watt was either a bit optimistic or intended to underpromise and overdeliver; few horses can maintain that effort for long. Regardless, comparison with a horse proved to be an enduring marketing tool.[

A healthy human can produce about 1.2 hp briefly (see orders of magnitude) and sustain about 0.1 hp indefinitely; trained athletes can manage up to about 2.5 hp briefly[6] and 0.3 hp for a period of several hours.

R. D. Stevenson and R. J. Wassersug published an article in Nature 364, 195-195 (15 July 1993) calculating the upper limit to an animal's power output. The peak power over a few seconds has been measured to be as high as 14.9 hp. However, for longer periods, an average horse produces less than one horsepower.

The following definitions have been widely used:

Mechanical horsepower

hp(I)≡ 33,000 ft-lbf/min = 550 ft·lbf/s

= 745.6999 W

Metric horsepower

hp(M)≡ 75 kgf·m/s

≡ 735.49875 W

Electrical horsepower

hp(E)≡ 746 WBoiler horsepower

hp(S)≡ 33,475 BTU/h = 9,809.5 W

Hydraulic horsepower= flow rate (US gal/min) × pressure ([[lbf/in2|psi]]) × 7/12,000

= 550 ft·lbf/s

= 745.6999 W

In certain situations it is necessary to distinguish between the various definitions of horsepower and thus a suffix is added: hp(I) for mechanical (or imperial) horsepower, hp(M) for metric horsepower, hp(S) for boiler (or steam) horsepower and hp(E) for electrical horsepower.

Hydraulic horsepower is equivalent to mechanical horsepower. The formula given above is for conversion to mechanical horsepower from the factors acting on a hydraulic system.

Assuming the third CGPM (1901, CR 70) definition of standard gravity,

1 HP≡ 33,000 ft·lbf/minby definition= 550 ft·lbf/ssince1 min = 60 s= 550×0.3048×0.45359237 m·kgf/s since1 ft= 0.3048 m and= 76.0402249068 kgf·m/s1 lb= 0.45359237 kg= 76.0402249068×9.80665 kg·m2/s3

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1,575 Posts

The HP wouldn't change because now the drum speed (RPM) has changed. HP is just a number, (torque x RPM) / 5252. With the same torque, HP goes down if RPM also goes down.We were talking about hp so I'm right but in away we are both right and wrong. Ok if hp is the result of torque/rpm and the torque would change why doesn't the HP change?

dammit, got tree'd.

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I was told the higher the ratio the lower the HP number on the rollers.

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OK, I got lost on that. If you go from 3.08 to 3.73, you're multiplying the torque going to the ground (the engine's spinning faster at the same MPH), so why isn't that a (apparent) HP increase?...Most of the time going from a 3.08 rear gear in a mustang to a 3.73 will net about a 4-6 rear wheel hp loss, ...

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Because HP is just a calculated number. Simply put, it's the amount of work done in a certain amount of time. HP = (torque x RPM) / 5252. More torque, but takes longer to do the same work = same horsepower.OK, I got lost on that. If you go from 3.08 to 3.73, you're multiplying the torque going to the ground (the engine's spinning faster at the same MPH), so why isn't that a (apparent) HP increase?

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