Petevb

Ah, got it... My curves are hp/wt. Your curves are hp/wt with aero and rolling resistance.

As you approach VMax weight virtually doesn't matter- it's almost a pure aero war. So while the two cars might have a near equal power to weight ratio, to achieve this the 9A2 producing more total power at many points in the curve, so has more power left over for acceleration after aero losses are accounted for. This is the main reason my chart shows the X51 ahead from 180 mph in 6th, while you show the 9A2 ahead or equal across the gear.

The gearing favors the 9A2 in this scenario, not letting the X51 use its power advantage. Drop 6th to a .92 ratio, letting the X51 also put out peak power at VMax, for example, and you'd get a slightly different outcome.

Thus the two charts are not saying quite the same thing. Assuming correct weights and dyno charts your method should predict high speed acceleration more accurately.

I'd still bet on the X51 in a 100-140 mph roll on, as I stated before, but that's splitting hairs.

benjiexpress

Petevb,

First of all, I apologize to hijack your thread.

I assume you have heard about engine stumble issue with 991.1 by now.

Would you mind if I ask your opinion on what is mainly causing the issue?

Based on poll survey done at other 991 forum, one third owners seem to have the issue. It is correct to say they are suffering from it. I am sure your input will be appreciated by me and many others.

BTW I am impressed by your technical posts. It was quite hard for me to follow but I now know for sure 991.1 engine is made to be turbocharged optionally and 991.2 is not clean sheet turbocharged.

Thanks in advance.

STG

Great question

Reference:

http://www.6speedonline.com/forums/9...00-rpm-33.html

Both Forums are owned by Internet Brands along with so many others

http://www.internetbrandsauto.com/sites

Dodaleca

Car and Driver says it's a bit more than 1 bar.
"Boost pressure is also tailored for each engine, with 13.1 psi in the Carrera and 16.0 psi in the S. "


In most industrial engines I deal with the power de-rating is 3% per 1000 ft above 1500 ft ASL for naturally aspirated engines and 1.5% per 1000 ft above 3000 ft ASL for turbocharged engines. Some come with larger turbos to get to 5000 ft ASL before de-rating.

Ray S

Best post of the whole thread!

There is so much "magazine racing" going on in here I had to check the top of the page to make sure I was still on Rennlist and not a Honda forum.

500

I thought this excerpt from the C&D article was particularly interesting:

The new engines are complete redesigns of the existing powerplants, although they retain the traditional flat-six layout and general dimensions of their predecessors. The engine block still consists of two parts, each with a crankcase half and a block of three cylinders. However, these cylinder bores are now coated with iron that is plasma-sprayed onto the aluminum surface. The raw aluminum cylinders are machined with slightly undercut grooves, so that the iron coating interlocks mechanically with the aluminum. According to Thomas Brandl, one of the engineers working on the new engine, this RSW (Rotating Single Wire) process is more durable than either Nikasil or the silicon-reinforced Locasil process used previously. Moreover, this change allowed Porsche to employ a stronger aluminum alloy for the block. It’s cast with metal outer molds and sand-cast cores, using a rotary process that reduces porosity. The resulting block has a closed deck and slices 3.3 pounds from the engine’s weight.

Nice to see some detail work of this nature.

lsmkr01

This further solidifies the importance of every pound or fraction there of over the back wheels. That's a lot of trouble to go through to shave

Happy911S

I saw in one of the previous posts on this thread that the 991.2 lapped the Nurburing 10 secs faster than the 991.1. The altitude ranges from about 1000 ft at the low to about 2000 ft at the high point so wouldn't a FI engine help in this situation?

I really don't care if the engine makes more power and if faster, I love my NA Powerkit engine and don't plan to give it up anytime soon -- certainly not for the minor change the 991.2 may, or may not, provide!

996tnz

On the handling front, a rear weight bias (typically around the 60% mark) is preferable for most situations given a skilled driver, so I'm not convinced Porsche would go to the point of changing their cylinder treatment just to save a pound or two. (http://www.caranddriver.com/features...11-gt3-feature ). That test would mean a lot more of course if the cars were on the same rubber, but there wouldn't be too much in it between the rear-engined GT3 and the lighter Cayman.

Porsche's main goal here is probably the ~5% fuel efficiency improvement that's possible with the Plasma Transfered Thermal Arc (Thermal Spray) bore treatment. Nissan has been doing it since 2009 with their GTR.

The main potential drawback of the process looks to be the risk of the coating sloughing off the walls, with the engine then wearing itself out quickly due to aluminum wearing directly on aluminum. After the non-Mezger 996 problems and the 991 engine GT3 recall I don't think Porsche would be game to do it if they weren't well satisfied they had it under control this time though.

Quite a nice summary of bore treatments in this research paper:

http://www.ewp.rpi.edu/hartford/user...ft_4_14_11.pdf

Thermal spray treatment review starts on page 27.

As for turbo drivability, Porsche has some of the best form in the world there and I predict that more than a few of those who actually test drive the 991.2 will be filled with lust. And that's even before cheap power gains from tuning and watching them zip past on track.

That said, unless someone brings out a proper aftermarket handbrake (e-brake) for them, they'll remain off my wish list. I swore my old 750iL would be the last car I bought without a proper lever.

Noah Fect

I agree the e-brake is an atrocity, but that's cutting off your nose to spite your face.

996tnz

There's time to go before that as I'm not missing out on too much yet. Each driver's priorities are personal but I'm still happy:

Direct single ratio rack and pinion steering - check!
RWD bias - check!
Handbrake lever for corrections on the move - check!
Enough power to break traction in third - check!
Fully defeatable PSM - check! (she's a bit special)
Scope for more power (those 4 doors keep getting quicker) - check!
Decent chance of survival if ambition exceeds talent - check!

I'd be happier if she was pre-drilled for a removable cage and came with racing buckets but other than that, few complaints and she still worries the newer metal, at least until its hits the 991 GT3 level.

That said, I do appreciate the newer cars and am glad to see Porsche finaly opening up its goody cupboard by more than a crack, in reply to the GTR with stuff like Porsche 4WS hitting the streets earlier than might otherwise have been the case.

wtdoom

I haven't laughed this much at a post in years . Thank you that was genius

randr

I found this thread both interesting and at various times amusing. So I thought I'd jot down a few bits and pieces from a number of articles I read prior to ordering my new 911 (and by way of disclosure I own a 981 GTS , have just ordered a 991.2 S and hold two CAMS I class licences -R+N).

Type -------991.2 S-------991.1 GTS
80-120kmh--2.3s----------2.4s (Porsche catalogue)
0-160kmh----8.2s----------8.4s (Sport Auto/Autozeitung)
0-200kmh---12.5s---------13.0s (Quattroroute/Autozeitung)
200-0kmh---128m---------134m (Sport Auto)
1/4mile----11.7@121-----11.9@118 (Quattroroute/Car and Driver)
18m slalom-73.2kmh-------72.9kmh (Sport Auto)
Hock. Short--1:09.6s------1:10.9s (Sport Auto)
Nevers-------1:20.52s------1:21.61s (Motorsport)
Peak HP---420HP@6,500--430HP@7,500 (Porsche catalogue)
Tqe-500Nm, 1700-5000---440Nm@5750rpm (Porsche catalogue)
CD-------------0.3------------0.3 (Porsche catalogue)

HP calculated from the area under the torque curve for the range 2000 rpm to 7500 rpm - 3l twin turbo (991.2 S 9A2) ~ 315HP, 3.8l NA (GT4 9A1) ~ 263HP. In the daily driven range (2000rpm to 5000rpm) the difference between the two mills is significant ~ 50HP. In the case of the X51 (as found in the 991.1 GTS) Vs the 9A2 (as found in the 991.2 S) the area under the torque curve for the former yields an average of 342HP versus 374HP for the new 9A2 (rpm range of 4000 to 7500 in the case of the 9A2 and 4000 to 7700 in the case of the X51).

The 9A2 three litre twin turbo is a good mill, it has better liners and a better fuel injection system than the 9A1 (e.g through optimal placement of the injectors which allows better and more efficient combustion and thus minimises early det.). Turbo lag has been minimised by the use of two relatively small turbines that only boost to a very modest 16psi running off the back of a 3l six cylinder engine. Any heat sink issues have been addressed by the placement of two large capacity air to air intercoolers mounted low on either side of the engine.

Porsche know what they are doing with turbocharged cars and the new 991 S outperforms the last GTS in every way except noise and even then the trade off is a lot less than people think. I liked the overall package so much I actually bought one. IMHO the improvements over the outgoing 991.1 are significant right down to the improved steering feedback and the responsiveness of the PDK. The engine is a complete non - issue and to be frank is an improvement over the 9A1 which is reflected in all the straight line performance stats.

Tangerine

The 991.2 is absolutely the better car in every measurable way. It's more subjective and silly things that people prefer with .1. For me, it's:

1) the sound (very subjective)
2) throttle response/character (again, subjective, some might like the feel better of the .2)
3) auto start/stop enabled by default (not kidding, this would drive me nuts)
4) holes in the back of the bumper (again, subjective!)
5) placement of tail pipes, assuming you get PSE, which is basically a must (subjective!)

After seeing the sport design bits for the .2, I think the 991.2 GTS is going to be a beast. The GTS variant will always be faster, better sounding, better handling, and better looking than the S. It's more appropriate to compare the 991.1 S to the 991.2 S, since that's the delta you'll see as soon as the 991.2 GTS appears.

randr

OK relative to the 991.1 S and based on the torque curves published in the 991.1 and 991.2 catalogues, the 9A2 (991.2 S) makes an average of 374HP in the range 4000rpm to 7500rpm in contrast the 9A1 (991.1 S) makes an average of 337HP in the range 4000rpm to 7700 rpm.

Or to put it another way, the 991.2 S makes 256HP per metric tonne in the rev range 4000rpm to 7500rpm (din weight PDK 1460kg). Whereas the 991.1 S makes 236HP per metric tonne in the rev range 4000rpm to 7700rpm (din weight PDK 1415kg).

And to the $64,000 question, what does the big daddy 991 GT3RS make?..........drum beat...........386HP (4000rpm to 8700rpm) or 272HP per metric tonne for the stated rev range.