Rennteam 2.0 - EN - Forum - Re: Excellence reviews 997.2 - Page1

Aug 13, 2008 1:42:51 AM

ADias: Rennteam Pro; Loc: Southwest USA , United States; Posts: 2495, Gallery; Registered on: Apr 9, 2004

Excellence reviews 997.2

The Nov. issue of Excellence has a thorough review of the 997.2 They delve deeply into the new engine architecture and rave about the PDK. This is the best review I've read. Subscribers should be getting the issue by now and it should be in newsstands soon.

Question for Grant: why is it that the PDK-equipped car has a lower (by 1m/h) top speed than the manual car, when its 6th gear ratio and final ratio are identical to the manual box? Of course, the speed difference is immaterial, but I fail to understand why that happens when the ratios are the same.

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Aug 13, 2008 1:53:33 AM

Cope: Newbie; Loc: WV , United States; Posts: 32, Gallery; Registered on: Nov 5, 2006; Reply to: ADias

Re: Excellence reviews 997.2

Got mine today. Good read!

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Aug 13, 2008 2:59:35 AM

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

Re: Excellence reviews 997.2

Quote:
ADias said:
Question for Grant: why is it that the PDK-equipped car has a lower (by 1m/h) top speed than the manual car, when its 6th gear ratio and final ratio are identical to the manual box? Of course, the speed difference is immaterial, but I fail to understand why that happens when the ratios are the same.

Tony - that is an excellent question. I have not heard a definitive explanation, but the one I have heard is that the PDK has a bit more internal friction than the manual.

All transmissions suffer internal losses (I think the average manual 911 loses about 15% of its horsepower between the crankshaft and the tires). This is primarily due to mechanical friction (heat) losses along the way (transmission, driveshafts, CV joints, bearings, etc.). Maybe the PDK loses just slightly more energy than manual (but much smaller loss than Tip).

The difference between 180mph and 181mph is probably around 3-5hp (around 1%)...

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Aug 13, 2008 9:43:48 AM

Jim_in_Iowa: Pilot; Loc: US; Posts: 336, Gallery; Registered on: May 18, 2005; Reply to: ADias

Re: Excellence reviews 997.2

At Parade, PCNA answered the speed question. It's a matter of gearing. The top gear was chosen for maximum economy, the first time a Porsche didn't reach maximum speed in the highest gear.

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Aug 13, 2008 10:19:21 AM

Ferdie: Rennteam VIP; Loc: Europe , Germany; Posts: 8234, Gallery; Registered on: Jul 2, 2004; Reply to: Grant

Re: Excellence reviews 997.2

Quote:
Grant said:
All transmissions suffer internal losses (I think the average manual 911 loses about 15% of its horsepower between the crankshaft and the tires). This is primarily due to mechanical friction (heat) losses along the way (transmission, driveshafts, CV joints, bearings, etc.). Maybe the PDK loses just slightly more energy than manual (but much smaller loss than Tip).

Indeed, I am under the same impression. Not to forget, the improvment in gas mileage for the PDK system is due to the longer 7th gear which is used in normal mode quite often. PDK systems are much more complex by themselves and need energy for the actuation of gears and clutches, done by a hydraulic system.

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Aug 13, 2008 3:17:35 PM

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

Re: Excellence reviews 997.2

Quote:
Jim_in_Iowa said:
At Parade, PCNA answered the speed question. It's a matter of gearing. The top gear was chosen for maximum economy, the first time a Porsche didn't reach maximum speed in the highest gear.

Jim - I think you are confused. A.Dias is asking why the top speed of the PDK in 6th gear (7th gear has a much lower top speed) is 1 mph slower than the manual in 6th gear. Both the manual 6th gear and PDK 6th gear (where top speed is achieved) have identical gearing. 7th gear in PDK is for fuel consumption and noise reductions.

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Aug 13, 2008 3:58:03 PM

reginos: Rennteam VIP; Loc: Nicosia , Cyprus; Posts: 12130, Gallery; Registered on: Mar 20, 2005; Reply to: Grant

Re: Excellence reviews 997.2

Quote:
Grant said:
Quote:
Jim_in_Iowa said:
At Parade, PCNA answered the speed question. It's a matter of gearing. The top gear was chosen for maximum economy, the first time a Porsche didn't reach maximum speed in the highest gear.

Jim - I think you are confused. A.Dias is asking why the top speed of the PDK in 6th gear (7th gear has a much lower top speed) is 1 mph slower than the manual in 6th gear. Both the manual 6th gear and PDK 6th gear (where top speed is achieved) have identical gearing. 7th gear in PDK is for fuel consumption and noise reductions.

Maybe the little extra weight of some 25kg?

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Aug 13, 2008 5:37:15 PM

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

Re: Excellence reviews 997.2

Quote:
reginos said:Maybe the little extra weight of some 25kg?

No, 25kg weight affects acceleration, but not top speed (just takes a bit longer to get there).

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Aug 13, 2008 5:56:16 PM

Revvv: Pilot; Loc: Ft. Lauderdale, FL , United States; Posts: 377, Gallery; Registered on: Sep 25, 2002; Reply to: Grant

Re: Excellence reviews 997.2

More drag, from central transmission cooling for PDK ?

Revvv

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Aug 13, 2008 8:34:28 PM

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

Re: Excellence reviews 997.2

Quote:
Revvv said:
More drag, from central transmission cooling for PDK ?

Revvv

Not sure about that, but just the fact that it needs central transmission cooling indicates that it gets hot (more friction).

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Aug 13, 2008 9:41:31 PM

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

Re: Excellence reviews 997.2

Quote:
Grant said:
All transmissions suffer internal losses (I think the average manual 911 loses about 15% of its horsepower between the crankshaft and the tires). This is primarily due to mechanical friction (heat) losses along the way (transmission, driveshafts, CV joints, bearings, etc.). Maybe the PDK loses just slightly more energy than manual (but much smaller loss than Tip).

A dual-clutch transmission has to have two concentric drive shafts (one to each clutch) where a conventional transmission has one. These two shafts are both rotating, but at different speeds, so they will also have additional bearings between them to enable the resulting relative movement and these bearings will cause additional friction losses.

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Aug 14, 2008 8:54:18 AM

reginos: Rennteam VIP; Loc: Nicosia , Cyprus; Posts: 12130, Gallery; Registered on: Mar 20, 2005; Reply to: ADias

Re: Excellence reviews 997.2

Quote:
ADias said:
The Nov. issue of Excellence has a thorough review of the 997.2 They delve deeply into the new engine architecture and rave about the PDK. This is the best review I've read. Subscribers should be getting the issue by now and it should be in newsstands soon.

Check it out here:

http://www.excellence-mag.com/art1/art1p1.html

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Aug 14, 2008 12:02:07 PM

GR: Senior; Loc: S Bucks, England , United Kingdom; Posts: 779, Gallery; Registered on: May 17, 2005; Reply to: reginos

Re: Excellence reviews 997.2

You'll also get losses from the pre-selected gear on the disengaged layshaft

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Aug 14, 2008 2:26:06 PM

JoeRockhead: Rennteam VIP; Loc: Topside , Monaco; Posts: 8033, Gallery; Registered on: Sep 17, 2007; Reply to: GR

Re: Excellence reviews 997.2

I read this article last night. The new engine is apparently easier/faster to assemble and some components are easier to work on. Are these added benefits on top of the weight reduction and economy increases, or were they requirements that were in scope for the engine design to save money in production and service?

Also, I see the benefit of the integrated cam and crank bearings but what does this mean to the future would-be engine builder and aftermarket tuners? Maybe not much but it's interesting to note. All in all, this new engine design is quite an achievement; I guess time will tell how reliable it is.

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Aug 14, 2008 3:28:46 PM

magik: Newbie; Loc: London, UK; Posts: 19, Gallery; Registered on: Apr 27, 2008; Reply to: Grant

Re: Excellence reviews 997.2

Quote:
Grant said:
Quote:
reginos said:Maybe the little extra weight of some 25kg?

No, 25kg weight affects acceleration, but not top speed (just takes a bit longer to get there).

Can that be right? If the 997 weighed 15 tons its not going to reach the same top speed as a 1.5ton car. In reality, surely weight has an impact.

just googled, this may help ..
http://www.physforum.com/index.php?showtopic=14909
not that I understand much of it, but it implies increased weight results in increased internal friction/ drivetrain losses.

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Aug 14, 2008 4:11:45 PM

Ferdie: Rennteam VIP; Loc: Europe , Germany; Posts: 8234, Gallery; Registered on: Jul 2, 2004; Reply to: magik

Re: Excellence reviews 997.2

The differences in speed for such a small weight difference are negligible. Those 25 kg are hardly recognizable in acceleration, let alone in top speed figures.

The decisive factor for top speed is resistance, aerodynamic, rolling and internal friction.

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Aug 14, 2008 4:53:47 PM

Crash: Rennteam VIP; Loc: Never been to , Antarctica; Posts: 8287, Gallery; Registered on: Oct 17, 2002; Reply to: magik

Re: Excellence reviews 997.2

I'd say gearing...

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Aug 14, 2008 5:02:57 PM

ADias: Rennteam Pro; Loc: Southwest USA , United States; Posts: 2495, Gallery; Registered on: Apr 9, 2004; Reply to: Crash

Re: Excellence reviews 997.2

Quote:
Crash said:
I'd say gearing...

Gearing is precisely the same - same 6th gear ratio and same final ratio. Still there's a difference.

Small weight diff is not the reason. Tranny losses only explain it if they are enough to limit the top available power to reach top speed - it may very well be the case and that means te PDK has significant higher losses.

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Aug 14, 2008 5:07:37 PM

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

Re: Excellence reviews 997.2

Quote:
ADias said:
Tranny losses only explain it if they are enough to limit the top available power to reach top speed - it may very well be the case and that means te PDK has significant higher losses.

Yes, but 1% is not that big a deal - more power is lost just by having one of the AWD models...

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Aug 14, 2008 5:53:29 PM

ADias: Rennteam Pro; Loc: Southwest USA , United States; Posts: 2495, Gallery; Registered on: Apr 9, 2004; Reply to: Grant

Re: Excellence reviews 997.2

Quote:
Grant said:
Quote:
ADias said:
Tranny losses only explain it if they are enough to limit the top available power to reach top speed - it may very well be the case and that means te PDK has significant higher losses.

Yes, but 1% is not that big a deal - more power is lost just by having one of the AWD models...

Absolutely. I'm not fretting about that at all, just realizing the facts and finding it interesting.

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Aug 14, 2008 7:33:05 PM

Jim48: Senior; Loc: Virginia, USA; Posts: 639, Gallery; Registered on: Oct 24, 2005; Reply to: fritz

Re: Excellence reviews 997.2

Quote:
fritz said:
Quote:
Grant said:
All transmissions suffer internal losses (I think the average manual 911 loses about 15% of its horsepower between the crankshaft and the tires). This is primarily due to mechanical friction (heat) losses along the way (transmission, driveshafts, CV joints, bearings, etc.). Maybe the PDK loses just slightly more energy than manual (but much smaller loss than Tip).

A dual-clutch transmission has to have two concentric drive shafts (one to each clutch) where a conventional transmission has one. These two shafts are both rotating, but at different speeds, so they will also have additional bearings between them to enable the resulting relative movement and these bearings will cause additional friction losses.

Agreed. The latest issue of Porsche Panorama, August 2008, had a review of the new version of the 997, and stated that for both models (Carrera and Carrera S), "In both cases Porsche says the PDK-equipped cars are slower because of frictional losses." But they are not that much slower, so for anyone desiring the faster shifting and launch control, PDK would seem to be the way to go.

Jim

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Aug 29, 2008 11:04:53 PM

_rocket: Newbie; Loc: UK; Posts: 17, Gallery; Registered on: Aug 26, 2008; Reply to: Jim48

Re: Excellence reviews 997.2

Nice review but they have wrongly reported the following:

Quote:
Porsche says the Carrera's 3.6- and the Carrera S's 3.8-liter engines are totally new, starting with a two-piece crankcase with fully integrated crankshaft bearings instead of the previous four-piece block with its bolt-in bearing housing.
That may alarm those who think about engines in terms of rebuilding them

997-2 PET shows that the bearing carrier is part of the block but the main bearings themselves are shells, not integrated.

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Aug 30, 2008 2:12:28 AM

ADias: Rennteam Pro; Loc: Southwest USA , United States; Posts: 2495, Gallery; Registered on: Apr 9, 2004; Reply to: _rocket

Re: Excellence reviews 997.2

Quote:
_rocket said:
Nice review but they have wrongly reported the following:

Quote:
Porsche says the Carrera's 3.6- and the Carrera S's 3.8-liter engines are totally new, starting with a two-piece crankcase with fully integrated crankshaft bearings instead of the previous four-piece block with its bolt-in bearing housing.
That may alarm those who think about engines in terms of rebuilding them

997-2 PET shows that the bearing carrier is part of the block but the main bearings themselves are shells, not integrated.

And what implication do you make of that?

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