Manifold

It can be difficult to account for all the variables when making those comparisons, but what got my attention is that the other GT3 you drove seem to be faster than yours in same session, with fairly equal (and good) drivers, despite the other GT3 not being your car, so I assume you were holding back a bit.

orthojoe

I agree, which is why I'm not putting in any verdicts yet. What has me the most worried is that if you look at tire rack's site, the Nspec 305 TREAD width is wider than K ferrari spec and R01 audi spec at a full 12.1" vs 11.2". The tread width on the 295 re71r is only 10.7", so we have a full 1.4" difference in width per tire. That explains why it looks stretched.

The GT3 that I was driving was running 305/30-19 RE71Rs, which have a tread width of 11.1", which is an inch less than Nspec 305s. Does the 0.4" make a difference? maybe.

MaxLTV

Not necessarily. These tires have way more rubber on the road than more street-optimized MPSC2, so even narrower tire can have same or more grip. There may be a need to transfer some grip from front to rear, though, and that's what sway bar accomplish. In general, using sway bars to adjust grip balance in neutral for total grip and is just moving it between front and rear (unlike trying to accomplish the same effect with tire pressures - there you would be actually giving up total grip due to having either front or rear at suboptimal pressure).

MaxLTV

So Don's car was not on MPSC2s? If so, that's interesting - seem like both your and Ben's best laps in a GT3 were on RE71R. Could really be a winner.

orthojoe

Correct. He is running re71r on 19" wheels with smaller rolling diameter. He runs 1:37s regardless of tire, though. Noah does 1:36 on cup2

Macca

So Joe, reading the GT4 thread it would seem there is now only currently a second between your GT3/4 sane track same drivers. Obviously you've been spending more time with the new car recently and made a number of changes. I see you are predicting they will end up posting similar times on your local tracks by the time you have finished. Clearly you are enjoying driving the GT4 and are close to optimising your track times in it. Briefly what are your thoughts between the two platforms and will you be considering a 991.2 GT3 in MT (which would appear to cover both bases)?

orthojoe

When I drove my buddy's GT3 that was well setup, I had a ton of fun in it. Possibly more so than the 4. Once the 3 is setup properly again, I plan to start using it more. However, the GT4 keeps on giving back and asking me to do more. It's easier to push the car harder in the 4. The 3's power can still be intimidating. Mech33 is faster in his 4 than his 3. I'm still faster in the 3, but not by much. We are talking about roughly one second give or take.
If the next gt4 has a detuned 3.8L version of the current gt3 engine, I see no reason to look at anything else.
The ship has sailed on the 991.2 gt3 for me. The lists are too long and I refuse to get robbed by greedy dealers. A manual vs pdk gt3 is of no consequence to me. I'll take either one and be happy either one. I am #3 on the list for a 991.2RS, though. That deposit was placed in June of 2015.

MaxLTV

I have exactly the same sentiment. Except I took back my GT3RS deposit, which probably was a mistake.

On a different note, it's funny how everyone was yelling how easy 991 GT3 is to drive, and yet still very few amateurs are within even 2 seconds per lap from pros. It's a very fast car but it's hard to make it fast - it's razor edge without being too punishing (so even tiny mistakes make you slow but you do not necessarily spin out and crash). That makes it fun for me.

orthojoe

Max, it's the same guys that think 2:10 at thill is fast and still can't heel toe properly.

Why did you take back the RS deposit?

MaxLTV

Because I moved to Canada and was not sure where I wanted the car, so I thought I'd order in Canada. Tough luck - here they did not even take my deposit. Anyway, I'm thinking of trying something different.

Macca

Joe & Max. This is interesting as Ive heard a few people who own both cars say similar.

I have driven the GT4 on a fast road run for a few hours and put my review up on this board last month. I did identify the GT4 seemed a relatively "easy" car to drive at my full ability within minutes of getting in the seat, whereas the GT3 has taken me a few years to get the best from on road and on track. Infact Im still getting a little quicker every year in the GT3, I think its a car you really need to have confidence with to truly get the best out of it.

Also the comment you make between the delta between a pro driver and an experienced amateur is telling. Last year Brendan Hartley (young kiwi who won Lemans in 2015) came home and attended a local Porsche driving school at one of our tracks as an instructor. He was asked to do a few hot laps that were timed. The car was a dealer stock 991 GT3 in stock trim and alignment with afresh set of Trofeo R fitted. He knocked almost 4s off my best ever lap on that 2.4 mile circuit and Im sure he had some left in him. my time is 10s per lap higher than the all time Porsche Cup car record set this year by a 991 GT3 Cup car in our Porsche race series running on Michelin blue slicks. That means he was roughly 7s slower in a factory trim road car on a semi slick than a race driver in a 1180kg 991 GT3 Cup car and he probably left over half a second on the table!

It does go to show drivers of a certain level can really extract the best out of the 911 chassis, but its pretty tricky to manage on the limit and needs knowledge of the chassis to get most out of the car...

GrantG

If the GT3 and GT4 run nearly the same laptimes, I would love to know how much each of these metrics is contributing to (or detracting from) performance:

1. Extra 90hp and 1,200 rpm of the GT3
2. Much lower and closer gears (and 7 of them) in the GT3
3. Roughly 200 pounds lighter GT4
4. Electronically controlled LSD in GT3 vs. weak mechanical LSD in GT4
5. Rear Engine vs Rear-Mid engine
6. Lightning fast shift and Launch Control of PDK-S vs. 3-pedal Manual in GT4
7. Wider wheels and tires of GT3
8. Rear Wheel Steering of GT3

I've always thought #6 was over-hyped (in terms of laptimes from rolling start). Will be very interesting to see if the Manual 991.2 GT3 is way behind in laptimes or not from the 991.2 GT3 with PDK-S. Of course #2 and #4 advantages will still apply...

MaxLTV

#1 does not help as much on tracks that Joe and I frequent - shorter tracks with not many straights and relatively fast corners (grip/aero tracks rather than engine & brakes).
#2 Top speed in each gear is rather similar between GT4 and GT3, right? The ratios are different but that's immaterial. What matters is the number of shifts per lap. And that goes back to #6 - there are not that many shifts per lap in either car, and GT3 is not noticeably slower if you shift even less than automatic mode would shift. So PDK advantage is small.
#4 - cannot really comment on that. GT3 is more stable under braking, probably due to eLSD, but GT4 is stable enough., so it should not influence times much if at all.
#7 - Total tire patch in cars Joe referred to was almost the same (same front and 285 vs. 305 rear, if I got that right). GT3 is definitely front tire limited, so wider rear did not help that much.

Anyway, at high-speed turn tracks like Sonoma, Thunderhil and probably even Laguna Seca, aero matters more than any of this. Just look at Viper ACR times or even high-aero E46 M3s.

GrantG

Thanks for addressing. On these two points, just a couple comments:

#2 Although speed in gears might be similar (not sure that they are really very close), the lower gear ratios to achieve them in the higher revving GT3 would result in more thrust in each gear (even if identical engine hp and torque), due to more torque multiplication. Number of shifts does not tell the whole story.

#7 Although both cars use same front tire, GT3's front wheel is 1/2" wider and 1" wider in rear (despite only 10mm wider tire). This should give a patch advantage to the GT3 (and GT4 is REALLY front tire limited - I wore fronts almost 3x as fast as rears with an alignment).

Macca

A couple of observations. Front tyre patch under braking surely has other inputs such as mass and deceleration (probably a square function) and the moments of inertia that relate to where the pivot point in the car is located (no doubt further forward in the GT4) may have an effect the moment that the wheel is turned from dead straight ahead.

It must also be remembered the GT4 and GT3 are almost identical torque per lb/kg regardless of the 90 bhp power difference. Particularly on smaller tighter tracks this is the key metric to why these cars are closer in performance than many suspect.

Superior chassis dynamic coupled with very good torque to weight ratio, lower weight with effectively identical tyre contract patch/grip when all physics inputs are modelled only really leaves manual losses due to up changes. This is interesting because the talker gearing at our local track means only three up changes per lap for the GT4 vs 5 for the PDK etc. GR4 up changes in sport mode are rev matched by the ECU and we have looked at the AIM traces, it appears only 0.2-0.3s losses per shift. On our local track it would appear that 1s a lap difference between the cars is made up of around 0.6s losses for GT4 in speed on main straights, minus 0.9s losses R due to shifting balanced by around 0.5s benefits from quicker cornering in 2-3 of the more technical corners where the 911 chassis struggles a bit and really needs huge skill and experience (more than I have but what a pro could muster) to exploit.

So IMO that is it. The GT4 is certainly s more predictable and confident inspiring car to put a quick lap time in. A good lap time can be put in with the GT3 after some use and familiarity with it but a truly excellent time will take quite a lot more skill and experience than that.

Mech/vs electronic diffs and RWS make almost no impact on certain tracks I suspect.

I'm not sure is there is power lost in the PDK system due to mechanical losses of the automated transmission.

Will there be a real world lap time difference between a MT and PDK-S 991.2 GT3 on track? Sure. I predict around 1s a 2-2.4mile track assumes 4 up changes with a rev holding mode like GT4. There may be a tenth or so advantage due to less weight etc.

That's my guess in any case. I expect the new GT3 to be around 1s a lap quicker than the old in PDK guise so I'm guessing the new car with MT will be no slower than the old, maybe fractionally quicker...