abqautoxer

The only real issue I see with the 987.2 non-S is the lack of front camber. You give up torque and hp over the 987.1 S to get some wheel size. The problem is the 19" wheels, if you can find equivalent 18s for cheap then no problem. We just clarified the wheel spacers for Porsches in the latest Fastrack via Tech bulletin and something I would get/use.

edfishjr

Porsche owners have unlimited money. We don't need to find 18 inchers that replicate the width and offset of the 19" wheels. We have people for that.

I agree that the lack of camber will still be a major downer. I think the PDK is a game-changer, however. It may render the standard method of creating a thrust rating based solely on 2nd gear calculations a little obsolete. That is, the car can be driven differently and in some degree overcome the lack of 2nd gear thrust compared to it's competition because it can be driven in 1st gear more of the time with little downside to shifting more often.

I read the Fastrack. Color me confused. Not sure what the issue was that needed clarification, but I'm thinking:
1. If the spacer is a separate option I can use a spacer or not.
2) The wheel still has to be the correct width. The 5mm spacer option doesn't give the right to add 5mm to the wheel width.
3) If the spacer is a "conflict" option with a particular wheel, as it is with the XRR 8.5/11.5 option wheel, then it can't be used with a wheel of that size because it couldn't be ordered that way. (The spacer option is not a conflict with the 8/11 wheels, as I read the order guide.)
Does this seem right?

sjfehr

I thought the purpose of the spacer/offset rules was simply to ensure the offset of the wheels +/- a small tolerance for cars that come OE with spacers? The only benefit of the spacer being considered part of the wheel is that it allows you to essentially adjust with a negative-width spacer if the aftermarket wheel has too much offset.

As to the gearing, 1st gear tops out at 39mph (987.2 PDK) and 44mph (987.2S PDK), so yeah, PDK's going to be in 1st gear on a lot of autocross courses. It'll be offset somewhat by having to haul an extra 66lbs or so of transmission around, though. The manuals top out at 39 & 41mph, so it'll help vs the base. Ironically, it will help least at the fast flowing national courses where it really matters the most.

abqautoxer

Check the PDK's gearing in 2nd, if it is shorter than the manual then it would be interesting, otherwise not so much for most national's courses IMO. If you are talking about a local site, then nevermind.

1. Yes. The OEM factory spacer caused confusion in SCCA because you are also allowed a 1/4" spacer per section 13 of the rule book. To make it simple and allow aftermarket options we clarified the OEM spacer is part of the wheel. This means you could either use a single spacer to combine the 5mm OEM along with a 1/4" to a single 11.5mm spacer or put that into the backspacing of the wheel or any combination to get to that maximum offset increase.

2. Correct, this does not affect wheel width, only backspacing/offset.

3. Correct. You can only use the OEM spacer benefit in a situation it would have been offered. For example the 986S did not offer this option except the 04 Spyder. So you could only run them on the 04 spyder and not any other 04 or 00-03 S.

edfishjr

Thanks very much.

abqautoxer

No problem, glad to help. If you are going to Nationals, there is the annual SEB/AC townhall 3:30pm Labor day in the Driver's Center. You can come talk to me and others there about such things though I imagine this year most topics will center around Street class.

edfishjr

My thinking is that if the PDK allows the Cayman to rev-match downshift into a 25 mph corner, come out in 1st on the way to 44 mph, and lose very little when shifting to 2nd, then it has the same (or slightly more) thrust over that range than a Grandsport/C6Z06 that stays in 2nd the whole time.

As I see it, we then have a car with grip and thrust at least competitive with the 'Vettes and an advantage in narrowness.

abqautoxer

Honestly the Cayman, S or non-S in 1st makes less thrust than the grandsport does anywhere in 2nd. The C6Z06 super tall 2nd and peaky motor hurts it down low but the GS doesn't suffer from that.

edfishjr

I'll check my numbers... I may have a math error. I was getting that in 1st, the PDK Cayman makes more peak thrust per lb of car weight (which is instantaneous acceleration) than the GS does in 2nd, not factoring any transmission losses and assuming both can deploy it all on street tires.

sjfehr

Saw an article about the RUF 3800 in this month's Excellence where RUF dropped a 991 3.8L into a 981. The RUF 981 makes 10hp more and weighs (IIRC) 160lbs less than the 991... yet is 3 tenths of a second slower to 60mph because the 991 has better traction. I daresay Porsche vs Corvette might not be as unbalanced as it looks.

I'm also looking again at the gearing charts on the 987.2.

Top of 2nd gear:
987.2S PDK: 76mph
987.2 PDK: 67mph

As much as I'd love another 50hp more than I have now... will 987.2 PDK be more competitive in AS than 987.2S PDK in SS?

edfishjr

I never studied SStock, so I have no opinion. I did watch Braun in a Boxster Spyder do quite well against a good SS field at Wilmington a few weeks ago. I'm also not interested in SStreet, though some of this may carry over.

At first, I thought the PDK Cayman with it's ridiculous, non-sports-car gearing was hopeless out-classed in AStreet. (I mean, really, if 2nd gear topped out about 62 in that car it would be much more fun, and the S should be geared for no more than 66.)

Two things have made me take another look. I got a report from three Corvette-driving friends who tested a PDK Cayman S at Barber and raved about how fantastic the gearbox was (even while they were not at all impressed with the power) being able to change gears at any time, so quickly, and not upset the car, and 2) I found out about the 8.5/11.5 wheels option. These two facts have caused me to take another look.

edfishjr

I haven't found an error.
I calculate peak thrust of a GS with 25.9" tires (335/30-18 Rivals) at 2773 lbs, or .8378 lb/lb when using the curb weight of 3311 lbs.

The Cayman with 25.5" tires (315/30-18 Rivals) has 1593 lbs of thrust in 2nd and 2642 lbs in 1st, or .881 lb/lb in 1st using a curb weight of 2998 lbs.

To rate the thrust of the Cayman PDK, I'm taking the average of 1st and 2nd gear peak thrust as a first approximation of how it might perform. This puts its considerably behind the GS in thrust, but not hopelessly behind.

Conclusion: In overall rating, using 3 parts grip, 1 part thrust and 1 part narrowness, I rate the GS only slightly ahead of the C5Z06 and the Cayman for AStreet. I think the Cayman is properly classed and, crucially, not as conservatively classed as perhaps intended.

The corollary of this is that the Cayman S PDK, by my rating system, would only be very slightly faster than the Cayman on an autocross course. Manual transmission cars need not apply, at least not for people at my skill level. Leaving either car in 2nd just isn't going to work.

edfishjr

I'm bummed. The more research I do, the more it appears that the Porsche order guides have been carrying incorrect wheel size definitions for many years. I read where the 2008 Turbo rear wheel was not 11" as listed, but actually 9.5"! The same may be true for some or all of the other "wide" wheel options listed as 11" or 11.5" wide. Sheesh!

This is a weird situation. The order guide would normally be the documentation needed to prove availability/definition of an option.

I've posted a question on Planet-9 to see if anyone can confirm more information.

BGLeduc

I have no documentation to refute that, but it does not sound right at all. A 2006 Cayman S has a 9" rear, I have hard time believing that a 997 TT would only have a 9 1/2" rear. Maybe the front is 9 1/2", but it would seem strange that the rear would only be a 9 1/2".

Brian

PedalFaster

Nitpick -- at least through the 986 generation, Porsche curb weights tended to be optimistic, as in real cars weighed more than the curb weights would lead you to believe. I haven't weighed a 987 or 981 to confirm if that's still the case, though.

100% agreed.