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Old 09-17-2005, 05:43 PM   #1 (permalink)
 
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'05 GTO Horsepower (?)

Greetings! First post here.

I recently saw the horsepower and torque specs for the 2005 Pontiac GTO:
Horsepower (advertised): 400 @ 5200 rpm
Torque (advertised): 400 ft-lbs @ 4000 rpm

Those familiar with auto math should notice something wrong right away.

Recall that the formula for horsepower is HP = Torque x rpm / 5252. So Torque = HP x 5252 / rpm.
Now, if the '05 GTO develops 400 horsepower at the stated engine speed, then the torque at 5200 should be 404 lb-ft, which is higher than
what the peak torque is supposed to be (400 ft lb @ 4000.)
So this means that either the peak torque is understated or the peak horsepower is overstated, assuming the engine speeds to be correct.

Explanations? (I'm awaiting a response from Pontiac but am not holding my breath.)
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Old 09-17-2005, 06:28 PM   #2 (permalink)
 
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They rounded down to 400.
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Old 09-17-2005, 07:22 PM   #3 (permalink)
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Quote:
Originally Posted by Quizcoot
Greetings! First post here.

I recently saw the horsepower and torque specs for the 2005 Pontiac GTO:
Horsepower (advertised): 400 @ 5200 rpm
Torque (advertised): 400 ft-lbs @ 4000 rpm

Those familiar with auto math should notice something wrong right away.

Recall that the formula for horsepower is HP = Torque x rpm / 5252. So Torque = HP x 5252 / rpm.
Now, if the '05 GTO develops 400 horsepower at the stated engine speed, then the torque at 5200 should be 404 lb-ft, which is higher than
what the peak torque is supposed to be (400 ft lb @ 4000.)
So this means that either the peak torque is understated or the peak horsepower is overstated, assuming the engine speeds to be correct.

Explanations? (I'm awaiting a response from Pontiac but am not holding my breath.)
well it will not matter when i mod my o5 to get 425 rhwp
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Old 09-17-2005, 09:28 PM   #4 (permalink)
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I did my own calculations. I found that when I tramp the gas pedal hard and shift accordingly (to the tach), I found the car jetsons like a bullet being shot out of a gun barrel. The ratio from one gear to another as calculated by the speed in which my foot depresses the gas pedal in conjunction with the depression of the clutch, I have determined that the GTO will take just about anything on the open road.

Bearing in mind, obstacles such as red and blue flashing lights can, and will hamper the full effect of the force needed to propel the GTO to a full launch at all times. Also, knowing that 100 mph can result in total torque being severely reduced by points being added to my record by those flashing red and blue lights, while exerting the most torque possible, will cripple the rated force that enables the GTO to be able to take just about anything on open road.

400 or 404 HP or torque, teet don't madder. IT GOES


no pun intended
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Old 09-18-2005, 08:43 AM   #5 (permalink)
 
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Yes they rounded down.

New rules also came out recently that might change some power numbers slightly. I think most will gain a few ponies on PAPER!
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Old 09-18-2005, 03:35 PM   #6 (permalink)
 
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Originally Posted by EEZ GOAT
well it will not matter when i mod my o5 to get 425 rhwp

You go, EEZ GOAT!




So we can say with reasonable assurance that the '05 GTO has one of the strongest factory engines in Pontiac GTO history.
(BTW, I tend to think that it's the rpm which is understated to some degree, in addition to the peak torque, but this is just a baseless hypothesis at best, on my part.)


Anyway, happy motoring!

---coot
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Old 09-18-2005, 10:41 PM   #7 (permalink)
 
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Quote:
Originally Posted by Quizcoot
Greetings! First post here.

I recently saw the horsepower and torque specs for the 2005 Pontiac GTO:
Horsepower (advertised): 400 @ 5200 rpm
Torque (advertised): 400 ft-lbs @ 4000 rpm

Those familiar with auto math should notice something wrong right away.

Recall that the formula for horsepower is HP = Torque x rpm / 5252. So Torque = HP x 5252 / rpm.
Now, if the '05 GTO develops 400 horsepower at the stated engine speed, then the torque at 5200 should be 404 lb-ft, which is higher than
what the peak torque is supposed to be (400 ft lb @ 4000.)
So this means that either the peak torque is understated or the peak horsepower is overstated, assuming the engine speeds to be correct.

Explanations? (I'm awaiting a response from Pontiac but am not holding my breath.)
Actually it's pretty simple (and stupid)-

The advertising genius that put the '05 brochure together got the LS2 HP & Torque numbers from GM Powertrain folks and just assumed that the engine speed at the particular peaks remained the same as on the '04 LS1 (take a look and you'll see that the advertised rpm is just like for the '04), while in reality the rpms should be just like on the '05 Vette (6000 and 4400, I believe). That's why they needed to increase the max rpm from 6000 to 6500, so that you woudn't drop below the torque peak point after a shift.
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Old 09-19-2005, 01:40 PM   #8 (permalink)
 
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Originally Posted by PWR_SHIFT
Actually it's pretty simple (and stupid)-

The advertising genius that put the '05 brochure together got the LS2 HP & Torque numbers from GM Powertrain folks and just assumed that the engine speed at the particular peaks remained the same as on the '04 LS1 (take a look and you'll see that the advertised rpm is just like for the '04), while in reality the rpms should be just like on the '05 Vette (6000 and 4400, I believe). That's why they needed to increase the max rpm from 6000 to 6500, so that you woudn't drop below the torque peak point after a shift.

Aha, just as I thought!

Actually, what I based my observation on was this:

To get a rough idea of the peak horsepower, use the formula HP = torque (peak) x (rpm-torque + rpm-hp) / 10504.
In other words, add the two rpm speeds, multiply this sum by the peak torque and divide by 10504 (twice 5252). This gives you a rough estimate of what to expect for peak horsepower.
(Note: If you you use this formula enough, you'll find that it does fail at times.)
So trying this on the 6.0 liter engine with the correct engine speeds:

6000 + 4400 = 10400
400 *10400 / 10504 = 396 hp.
Close enough!

Happy motoring!

---coot
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