AutoQuest MS

About 45lbs of rotational mass between the two, I'd imagine that would stand for a bit of a difference

orthojoe

It doesn't. Because that mass is towards the center, it doesn't make that big of a difference.
Do you think there would be a big difference if the tires had full tread vs worn tread because of the weight of the tread that has worn away? Would a car pull away just because it had lighter tires because the tread is worn? That is the equivalent in terms of weight advantage from the pccb when taking rotational mass into account. Our resident engineer/physics expert PetevB did the math and has a great thread on it.

AutoQuest MS

I guess I should have highlighted the word "bit" in that statement, as yes I do acknowledge that from a straight line perspective. On a race track it comes into play more, that we can feel right away.

Taffy66

Rotational inertia is Massx(Radiusx2) so the further the reduction of mass from the axis the higher the effect on reducing the inertia..If you was to put 18 inch rims on the GT3 you would reduce the MoI significantly..PCCBs are closer to the axis compared to tires but even so at 45lbs still reduce the rotational inertia.

Petevb

The manual is quoted as 2 km/h faster on the top end per Porsche- if that number was exact it would equate to a 2% difference in power to the ground after the manual's lighter weight is accounted for. Dyno data seems to support a higher loss, in the range of 4-5%, however a "perfect" comparison is nearly impossible- it's very difficult to take engine to engine variability out of any equation without doing a transmission swap (engine output also has a tolerance range). Thus I think we know the actual additional loss is between 2% and 5%, but we can't say more than that with certainty. 2% would be 10 hp.

Unlike a modern engine oil pump the PDK's oil pump is not actuated- it spins at all times to provide the motive power to operate the PDK, and like other parasitic losses it will increase with rpm.

Psorcery

Would you like to meet up and do some races against a tuned .2 GTS?

Brosef

theories like this have existed since Dual clutch transmissions came on the seen, but has there ever been a documented case of a manual actually accelerating faster than a dual clutch? it seems like the argument for why a manual should be faster is made based on theory, but then the actual facts (i.e. test data) consistently show the dual clutch is faster. I'm genuinely curious if a manual has ever triumphed in a like for like comparison?

Brosef

theories like this have existed since Dual clutch transmissions came on the seen, but has there ever been a documented case of a manual actually accelerating faster than a dual clutch? it seems like the argument for why a manual should be faster is made based on theory, but then the actual facts (i.e. test data) consistently show the dual clutch is faster. I'm genuinely curious if a manual has ever triumphed in a like for like comparison?

drdonger

Definitely not from a stand still. With no lift shift from a roll, I'm curious which would be faster between the 991.2 GT3 PDK and 991.2 GT3 manual.


Shift like him^ and it would be a good race.

Petevb

Doing the math I get slightly over a 2x multiplier vs the straight weight difference of PCCBs vs cast iron. In a straight line specing the PCCBs is equivalent to removing ~84 lbs from the chassis when the iron rotors are fresh. When the iron rotors are worn to their wear limit the advantage drops to the equivalent of (EDIT): 78 lbs.

Airbag997

The PDK "may" do more Work (Power*Time) than a manual because Force is applied longer due to significantly shorter shift times versus a manual. It's the total HP that is applied to the ground over a finite amount of time that needs to be calculated, not just the absolute power at any given time. It's an area under the curve problem. Finite Integral.

Petevb

I'm not sure it qualifies as a theory, but I never said the manual does accelerate faster. Obviously the PDK has both a faster shift time and another gear to balance the equation out (though with more weight). Porsche themselves have said that from a roll the two cars are very similar, but a controlled test is very difficult to arrange because of the different gearing. If one were to try then top gear (6th for the manual and 7th for the PDK) would be the best bet, but the manual's gear is 1% taller so it would be at a disadvantage. If one could roll on from 120 mph, however (good luck) that would be very interesting to witness. At that point you're on the torque plateau, and theory says the manual might be able to pull despite its gearing disadvantage. Just in case anyone with access to a clear autobahn cares to play games early one morning...

AutoQuest MS

I grew up not far from Maple Grove Raceway and used to run there myself on occasion. "100lbs is worth .1 in the 1/4" would be thrown around on a daily basis talking to the old heads there. A bit of a difference, enough to beat the other guy but not put car lengths on him by any means like in that video haha

ajw45

Hard to document because weight, gearing, and other things would need to equalized.... and no one cares. There's theory and then there's fact fortunately. Fact is a dual clutch takes more power to operate though perhaps to an insignificant degree.....

https://www.bimmerboost.com/showthre...ion)-vs-Manual

Petevb

Yep. Worth the equivalent of about 12 hp- enough to be worthwhile, but not crushing.