Rennteam 2.0 - EN - Forum - Re: Net Horsepower of porsche - Page1

Apr 25, 2005 4:57:47 PM

Outlaw_Hawk: Co-Pilot; Loc: Qatar; Posts: 188, Gallery; Registered on: Feb 6, 2005

Net Horsepower of porsche

To know exactly which is a faster car or quicker we shouldn't look at horsepower alone but to know its weight that holds the horsepower back and if we know both then we can know the net horsepower depending on data which is enough to know approximately 80% of the correct answer.
The formula to get the net horsepower is (horsepower / weight * 1000)
So let's do the math

Porsche 996

Carrera / Targa (320/1440*1000) = 222
Carrera 4S (320/1495*1000) = 214
Carrera 4S Cabriolet (320/1565*1000) = 204
GT3 (381/1380*1000) = 276
Turbo (420/1590*1000) = 264
Turbo Cabriolet (420/1660*1000) = 253
Turbo S (450/1590*1000) = 283
Turbo S Cabriolet (450/1660*1000) = 271
GT2 (483/1420*1000) = 340

Porsche Boxter

Boxter (240/1295*1000) = 185
Boxter S (280/1345*1000) = 208

Porsche Cayenne

Cayenne (250/2160*1000) = 116
Cayenne S (340/2225*1000) = 153
Cayenne Turbo (450/2355*1000) = 191

Porsche 997

Carrera (325/1395*1000) = 233
Carrera Cabriolet (325/1480*1000) = 220
Carrera S (355/1420*1000) = 250
Carrera S Cabriolet (355/1505*1000) = 236
Carrera S (X51) (381/1420*1000) = 268

Carrera GT (612/1380*1000) = 443

(All figures are rounded)

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Apr 25, 2005 10:23:16 PM

Dilinger: Rennteam Pro; Loc: Athens,Greece , Greece; Posts: 2034, Gallery; Registered on: Dec 23, 2004; Reply to: Outlaw_Hawk

Re: Net Horsepower of porsche

okey nice calculations

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Apr 26, 2005 1:11:03 AM

Silver Bullet: Veteran; Loc: Canada; Posts: 1126, Gallery; Registered on: Nov 24, 2004; Reply to: Dilinger

Re: Net Horsepower of porsche

Nice work, but as I understand it, those numbers, based on horsepower, will explain top speed. To consider acceleration, one would need to look at torque.

Have I got this right?

-SB

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Apr 26, 2005 7:38:08 PM

Grant: Rennteam VIP; Loc: Denver, CO , United States; Posts: 12586, Gallery; Registered on: Aug 21, 2002; Reply to: Silver Bullet

Re: Net Horsepower of porsche

Quote:
Silver Bullet said:
Nice work, but as I understand it, those numbers, based on horsepower, will explain top speed. To consider acceleration, one would need to look at torque.

Have I got this right?

-SB

Those calculations will give a fair estimate of acceleration and track performance. Torque is important, but not as important as weight, horsepower and gearing (which acts as a torque multiplier).

Horsepower is a measure of how much torque a motor can make at a given rpm (higher torque at higher rpm means lots of hp), so in that sense, torque is critical. Lots of peak torque without the ability to rev high (and continue to make high torque) is not as good though...

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Apr 26, 2005 8:05:05 PM

fritz: Rennteam VIP; Loc: BaWü , Germany; Posts: 10248, Gallery; Registered on: Jul 23, 2003; Reply to: Outlaw_Hawk

Re: Net Horsepower of porsche

OutlawHawk,

What you refer to as "net horsepower", calculated using your formula, is in fact a car's power-to-weight ratio expressed in bhp per metric tonne.

It is indeed a very good indicator of a car's likely ability to accelerate quickly.

Top speed, on the other hand, is decided primarily by horse power in relation the car's aerodynamic drag, and secondarily by mechanical friction losses in the transmission and tires. Weight does not play a direct role in limiting top speed.

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Apr 26, 2005 9:00:48 PM

wtsnet: Rennteam Pro; Loc: Bath, UK; Posts: 2430, Gallery; Registered on: Nov 19, 2004; Reply to: fritz

Re: Net Horsepower of porsche

If I remember from high-school physics:
1) Torque is the 'turning' force. (But you all know that!)
2) Power = Force * Velocity
3) Aceleration = Force / Mass

I know this is the root of what you guys just said! But it explains how the 'power vs speed' and 'torque vs speed' graphs are related when you see them superimposed.

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Apr 26, 2005 10:31:51 PM

Grant: Rennteam VIP; Loc: Denver, CO , United States; Posts: 12586, Gallery; Registered on: Aug 21, 2002; Reply to: wtsnet

Re: Net Horsepower of porsche

Quote:
wtsnet said:
If I remember from high-school physics:
1) Torque is the 'turning' force. (But you all know that!)
2) Power = Force * Velocity
3) Aceleration = Force / Mass

I know this is the root of what you guys just said! But it explains how the 'power vs speed' and 'torque vs speed' graphs are related when you see them superimposed.

I think that's basically correct, but I thought power=force over time (instead of velocity) - or maybe that's the formula for Work?. I know Momementum=mass*velocity...

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Apr 27, 2005 6:31:27 AM

wtsnet: Rennteam Pro; Loc: Bath, UK; Posts: 2430, Gallery; Registered on: Nov 19, 2004; Reply to: Grant

Re: Net Horsepower of porsche

Quote:
Grant said:
Quote:
wtsnet said:
If I remember from high-school physics:
1) Torque is the 'turning' force. (But you all know that!)
2) Power = Force * Velocity
3) Aceleration = Force / Mass

I know this is the root of what you guys just said! But it explains how the 'power vs speed' and 'torque vs speed' graphs are related when you see them superimposed.

I think that's basically correct, but I thought power=force over time (instead of velocity) - or maybe that's the formula for Work?. I know Momementum=mass*velocity...

Hey, I'm supplementing hi-school with a dose of good old internet knowledge here, but:

4) Work = Force * Distance
5) Power = Work / Time

and we can re-jig 4) and 5) to get

6) Power = Force * Distance / Time = Force * Velocity

I swear I was cleverer at school! That's what too much beer does to you!

Obviously this doesn't go into gearing, friction, and wind resistance.... Anyone?

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Apr 27, 2005 6:57:38 AM

Moogle: Rennteam Master; Loc: Bay Area , United States; Posts: 5019, Gallery; Registered on: Aug 9, 2003; Reply to: wtsnet

Re: Net Horsepower of porsche

wow, very nice to see those figures

nice to see these things in numbers.

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Apr 27, 2005 7:05:29 AM

Yargk: Pilot; Loc: SF Bay Area, CA, USA; Posts: 486, Gallery; Registered on: May 18, 2003; Reply to: wtsnet

Re: Net Horsepower of porsche

See the problem with using torque is that if you make 100 foot pounds of torque at 5000 rpm, you'll be slower than the car that makes 100 foot pounds of torque at 10000 rpm. The reason is that the flywheel is going faster in the 10000 rpm car so you will have different gearing the in 10000 rpm car so actually that car will have double the torque at the wheels. A good way to think about hp is that it's a cheat to understand roughly the effects of gearing, torque, and at what rpm that torque is made. Hp = torque X rpm X a constant so the HP will be twice as much in the 10000 rpm car. People refer to torque mostly because what they mean if a car has a lot of torque is that it has a wide powerband. Since you're not always making peak power, this is important, but hp is still the best first number to use. hp with weight gives approx acceleration, hp with drag gives top speed.

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Apr 27, 2005 12:21:15 PM

madadd: Co-Pilot; Loc: uk; Posts: 240, Gallery; Registered on: Jan 4, 2005; Reply to: Yargk

Re: Net Horsepower of porsche

Is there not also some truth in that the space under the HP curve is a good indicator of performance.

I have driven a couple of cars with high horse power, but they have been tuned to give high HP at the expense of everything else. (Turbocharged engines).

In these cases, cars with lesser HP were actually faster in the real world as the tuned car max HP was reached for such a short time, and so far up the rev range.

I once had a car (an Integrale) re-mapped to drop around 20bhp. Because the power was distributed so much better the car was so much quicker in day to day driving.

Looking at the old 996 powerkit, It makes me wonder how much gain you really feel, as all the extra HP is at the very top end.

The reason why I ordered a 997S rather than getting the 996TT is that the power to weight ratios are just too near!

...Add

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Apr 27, 2005 1:22:28 PM

TB993tt: Rennteam Pro; Loc: manchester , United Kingdom; Posts: 2280, Gallery; Registered on: Jul 22, 2002; Reply to: Outlaw_Hawk

Re: Net Horsepower of porsche

A great topic. I would like to illustrate something which has already been mentioned and is very important on this subject: HP is a function of torque so they are interchangable, but like anything mathematical it gets confusing when people start making statements like torque is more important than hp - The statement is true but what the person is actually saying is that it is the lower end peak torque which is important. Here is my example. PSI Motorsport do a 540hp kit for the 993tt which is agreat kit and gives impressive acceleration.My car also has 540hp courtesey of RS Tuning. will the acceleration be the same ? (we have to rule out the RS overboost programming here which would make it no contest and just look at full throttle power curves)
The secret is in examining the whole power (or torque) curve.
rpm PSI RS
4750 472 500
5000 475 520
5250 490 525
5500 512 525
6000 538 535
6500 460 541
6750 limit 537

So ignoring the PSI curve tailing off at the top end, one can see the higher torque at the low end giving the higher power numbers on the RS car - so 2 540hp cars, one with K24s and fairly minimal mods, the other with twin plug, flame rings, special 996tt K24/26s
Its all in the detail.
Value for money, its got to be the PSI kit

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Apr 27, 2005 2:57:41 PM

iia: Pilot; Loc: Canada; Posts: 342, Gallery; Registered on: Aug 24, 2004; Reply to: TB993tt

Re: Net Horsepower of porsche

The unit of torque is lb-ft in UK and NA. It is the twisting force produced by an engine's output shaft. 1 lb-ft is equal to holding one end of 1 ft ruler that has 1 lb mass at the other end. The key is torque can be exit even there is no movement! Hard to imagine!?

One horsepower is defined as 550ft-lb/sec which means the power to raise 550lb with a distance of 1 ft in 1 sec or mathamtically equivalent. The key is the amount of work done in term of time and distance.

As housepower = (torque x rpm) / 5252, the peak housepower always comes at the high rpm. It won't be a big concern for low end torque in racing as people will always run at high rpm range. But, in city driving, you run in lower to mid rpm range. So, with a given rpm, you want your car to have as much low end torque as possible to have higher housepower (the amount of work done in term of time and distance).

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Apr 27, 2005 3:55:43 PM

Grant: Rennteam VIP; Loc: Denver, CO , United States; Posts: 12586, Gallery; Registered on: Aug 21, 2002; Reply to: wtsnet

Re: Net Horsepower of porsche

Quote:
wtsnet said:Hey, I'm supplementing hi-school with a dose of good old internet knowledge here, but:

4) Work = Force * Distance
5) Power = Work / Time

and we can re-jig 4) and 5) to get

6) Power = Force * Distance / Time = Force * Velocity

I swear I was cleverer at school! That's what too much beer does to you!

Thanks for straightening me out - yeah, I'll blame it on the beer

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Apr 27, 2005 4:02:37 PM

wtsnet: Rennteam Pro; Loc: Bath, UK; Posts: 2430, Gallery; Registered on: Nov 19, 2004; Reply to: iia

Re: Net Horsepower of porsche

Quote:
iia said:
The unit of torque is lb-ft in UK

We use metric here, ie Newton-Meters (Nm)

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Apr 27, 2005 4:49:26 PM

STRADALE: Rennteam VIP; Loc: NY , United States; Posts: 11075, Gallery; Registered on: Mar 9, 2005; Reply to: Outlaw_Hawk

Re: Net Horsepower of porsche

One of the real interesting comparisons for me is:
996 Turbo Cabriolet @253 vs. 997 Carrera S @250

Also how low the Carrera 4S Cabriolet @ 204.

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Apr 27, 2005 4:49:34 PM

Turbo Al: Rennteam Pro; Loc: Rochester, New York , United States; Posts: 2531, Gallery; Registered on: Apr 3, 2005; Reply to: wtsnet

Re: Net Horsepower of porsche

I agree this is a great thread. I can't wait for the 997TT specs. re. HP and torque (and the car) to come out

. I have more of a need for low-rpm peak torque for accelerating (I don't track race and reside in the USA with roads with ridiculously low speed limits

). I wonder what aftermarket tuning (including this website's sponsor!

) of the 997TT could be accomplished for my purposes.

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Apr 27, 2005 6:01:29 PM

iia: Pilot; Loc: Canada; Posts: 342, Gallery; Registered on: Aug 24, 2004; Reply to: wtsnet

Re: Net Horsepower of porsche

Quote:
wtsnet said:
Quote:
iia said:
The unit of torque is lb-ft in UK

We use metric here, ie Newton-Meters (Nm)

Oops! Sorry.

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Apr 27, 2005 6:14:58 PM

wtsnet: Rennteam Pro; Loc: Bath, UK; Posts: 2430, Gallery; Registered on: Nov 19, 2004; Reply to: iia

Re: Net Horsepower of porsche

Quote:
iia said:
Oops! Sorry.

Hey, we confuse ourselves half the time. The market traders are very upset that they can't sell bananas by the lb any more! We tend to mix and match depending on what suits us. If it's hot, we call the temperature in Fahrenheit. If it's cold, it's in Celcius. Barking!

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Apr 27, 2005 9:02:52 PM

fritz: Rennteam VIP; Loc: BaWü , Germany; Posts: 10248, Gallery; Registered on: Jul 23, 2003; Reply to: STRADALE

Re: Net Horsepower of porsche

Quote:
Stradale said:
One of the real interesting comparisons for me is:
996 Turbo Cabriolet @253 vs. 997 Carrera S @250

Also how low the Carrera 4S Cabriolet @ 204.

Not so surprising. Put the standard Carrera engine in a heavier, wider, cabriolet body, and the power-to-weight ratio automatically has to go down.

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Apr 28, 2005 1:44:09 AM

Yargk: Pilot; Loc: SF Bay Area, CA, USA; Posts: 486, Gallery; Registered on: May 18, 2003; Reply to: madadd

Re: Net Horsepower of porsche

Quote:
madadd said:
Is there not also some truth in that the space under the HP curve is a good indicator of performance.

I have driven a couple of cars with high horse power, but they have been tuned to give high HP at the expense of everything else. (Turbocharged engines).

In these cases, cars with lesser HP were actually faster in the real world as the tuned car max HP was reached for such a short time, and so far up the rev range.

I once had a car (an Integrale) re-mapped to drop around 20bhp. Because the power was distributed so much better the car was so much quicker in day to day driving.

Looking at the old 996 powerkit, It makes me wonder how much gain you really feel, as all the extra HP is at the very top end.

The reason why I ordered a 997S rather than getting the 996TT is that the power to weight ratios are just too near!

...Add

You're exactly right, I'm just saying hp is the best first number to use. Really I'm just saying that peak hp is a better number to use than peak torque, if you had either a graph of hp or torque vs. rpm, that has all the information you need which is better than either single number.

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