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  #13  
Old 04-12-2011, 01:14 PM
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Re: HEMI Torque Curve from dyno

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Originally Posted by Walt View Post
Remember that the torque and HP curves must cross at 5,252 RPM.

HP = (torque x rpm) / 5252. Torque must be in ft-lbs.
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Originally Posted by 77rednecktruck View Post
where did that come from???
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Originally Posted by Bmwister View Post
You and I and other techies probably already know where the 5252 constant comes from, but for those who do not: http://www.howstuffworks.com/question622.htm


--
That doesn't jive with the charts. The chart above shows the same torque at 5252 rpm as it does at around 3250 rpm, so according to your formula, the hp at both rpm's should be the same, but as you can see from the chart, the hp are vastly different. Or does this formula only work when you are at the maximum hp or maximum torque rpm?
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Old 04-12-2011, 05:13 PM
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Re: HEMI Torque Curve from dyno

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Originally Posted by Nouveau Redneck View Post
That doesn't jive with the charts. The chart above shows the same torque at 5252 rpm as it does at around 3250 rpm, so according to your formula, the hp at both rpm's should be the same, but as you can see from the chart, the hp are vastly different. Or does this formula only work when you are at the maximum hp or maximum torque rpm?
That formula says the HP WILL NOT be the same at different RPM's with the same torque.

Using your example, the same torque, 360 at 3250 and 5252 you end up with these 2 HP figures

(360*3250)/5252 = 222.77 HP
(360*5252)/5252 = 360 HP

I know math is tough for a redneck, even a new one
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Old 04-13-2011, 03:57 PM
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Re: HEMI Torque Curve from dyno

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Originally Posted by mjw930 View Post
That formula says the HP WILL NOT be the same at different RPM's with the same torque.

Using your example, the same torque, 360 at 3250 and 5252 you end up with these 2 HP figures

(360*3250)/5252 = 222.77 HP
(360*5252)/5252 = 360 HP

I know math is tough for a redneck, even a new one
I think there might be a bit of misunderstanding about the nature of the measurements here.

This is because Horsepower is not a measurement of force applied (that's torque) but work completed. Every time that crankshaft spins, you get more work done. Higher RPM = more work done = more HP.

This is why "spinner" engines tend to generate more HP, even with comparatively meager torque numbers. It doesn't apply much force, but it applies what force it has pretty darn fast, so more gets done.

If we're stacking bricks on a pallet, if you stack 10 bricks at one go but it takes you 10 seconds to do it and I can stack only 4 bricks a go but I can do that in 3 seconds, I'll be stacking quite a few more bricks than you will, even though you're stronger.

MJW is correct. RPM matters a great deal in HP measurements because if you're measuring the amount of work that gets done, the speed of that work getting done is a rather large factor.
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Old 04-16-2011, 06:32 PM
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Re: HEMI Torque Curve from dyno

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Originally Posted by Technosavant View Post
I think there might be a bit of misunderstanding about the nature of the measurements here.

This is because Horsepower is not a measurement of force applied (that's torque) but work completed. Every time that crankshaft spins, you get more work done. Higher RPM = more work done = more HP....MJW is correct. RPM matters a great deal in HP measurements because if you're measuring the amount of work that gets done, the speed of that work getting done is a rather large factor.
Good. Torque gets you off the line, HP keeps it going.

It takes << half of the engine's rated HP to keep it going at highway speeds.

Minor correction: HP is power (work per unit time). Work is a measure of the total energy (HP-hr or ft-lbs.).
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