Sorry I've done a search on both here and Rennli__st and haven't found quite the right answers yet. I just want to get a quick basic primer on this platform. I'm not new to modding as I have a 1300whp+ GTR as well (soon to be 1600whp).

A few questions:
1) Where exactly is the restriction in the exhaust? Is it only the stock catalytic converters or is it also the piping/muffler after? Can I just make straight pipe cat links and use it WITH the stock muffler/tip section and get 99% of the performance/restriction removal versus an aftermarket exhaust? Yes I know I have to clear the CEL with Cobb or whatever. No big deal.

2) What diameter piping is the stock exhaust?

3) In turbo speak, what is the size of the factory turbos (compress/turbine wheel inducer/exducer sizes?

4) What exactly is the logic of the SOFTWARE on how the VTG opens and closes its vanes? Is the ECU controlling the electric motor in a linear way vs engine speed? Or is it an on/off switch when you are WOT? I ask this because when I drive my 997.2 TTS it feels like it's an on off switch.

5) I see people with bolt on's here running 21-23psi. This tells me it's a decently sized factory turbo. Is this the point when the factory turbos begins creating all heat and no power (assuming no exhaust restrictions)? Most FBO GTR's run 18psi on factory turbos because after that is pretty much all heat. On kill mode or a glory pass a GTR may run a few psi more. So I guess my question kind of is, for the factory 997.2 turbo is 22psi the equivalent of 18psi in a GTR as far as efficiency goes (standard conservative boost level) or is 22psi like a glory pass type of boost level for the factory turbo?

6) In a road course situation where there is repeated WOT runs, do factory 997.2 intercoolers get heat soaked enough to make the car go into limp mode if the weather is 95+ degrees outside? I'm trying to get a feel for just how good the 997.2 intercoolers are. Does this change if you up the boost to 21-23psi vs factory boost?

7) What is the logic behind how the 997.2 sends power to the front wheels? Are there sensors where it detects wheelspin then it engages a diff? Also does it have a diff in the front to send power independently between front left and front right wheels?

9) Is the diff that sends power to the front clutch or gear based? Basically, if you do a lot of launches and/or burnouts (if that's even possible) will it fry any clutch based diff?

10) How strong are the rear axles, front axles, and center drive shaft?

11) When people say you need to cut open the PDK transmission in order to access the clutches, are people saying you have to cut open the transmission casing? Or are they just saying you have to cut open clutch basket to access the discs?

12) How many people have blown up their Porsche .2's (9A1 engines) just doing full bolt on's and running 21-23psi? Are there any cover up's in the Porsche community just like there are in the GTR community?

13) Are factory exhaust manifolds a restriction? If so, at roughly what point do they become a restriction? I see vendors selling headers without proving they are a restriction. Those BBi headers sure do LOOK nice though.

Thanks,
Isaac

 

I am not an expert...

Here are some basic answers to get you started.

The exhaust is one piece. You have to replace the entire thing or hack up the factory and re weld. Most guys that run straight pipes just get a full new exhaust with no mufflers or cats. But this is why everyone gets new exhausts and then choose what kind of muffling/cats they want. Many aftermarket switch it to a component design to be able to switch in race pipes or cats which is easy.

Not sure of the factory size but the .2 engine/exhaust is quieter that .1. The cats are 600cell i believe.

Most would say headers are not necessary until you start building the motor. And i dont think ppl are building the 9a1 motor due to fueling restrictions with DI.

Fueling seems to be the most talked about limit on the .2s right now. There is a limit to the PDK but it seems relatively robust. (Cant quite remember but i think it was around the 700hp point).

The intercoolers are pretty good and dont seem too prone to heatsoak due to the plastic end tanks. Most guys start upgrading them when they want better flow or do turbo swaps going to welded metal end tanks so they dont blow the plastic off. But as far as cooling goes they are just fine for 95 deg road courses.

No one is really having problems with 997.2 engines but i think that is because people really arent pushing them like 997.1s due to the above pdk/fuel limits.

Hope this info is mostly accurate and helps a little.

 

One more. The axles dont seem to be much of a problem unless the car is super drag racing with drag radials and the like. As far as a bolt on modded car that does some fun launch control and spirited driving they are fine. Really it comes down to tire and track prep. So if you are going to seriously drag race then they wouldnt hold up. Some leave them though because axles are cheaper to replace than other driveline components.

 

Thanks for that Yogi. I didn't realize the exhaust was one piece from the factory. Has anyone tried to just clear out the cats (i.e. Remove the cat materials) and whether that frees up all the restrictions?

 

Yogi, the OEM exhaust is NOT one piece.

 

And the OEM exhaust is made by Akrapovic, which is the best of the best. I would hate to replace such a nice piece with a ****ty aftermarket one unless I absolutely have to.

 

No it isn't. It's made by Boyesen. It's pretty restrictive and typically the first thing people replace when modding. You could just get catless pipes and keep the stock muffler if you wanted to save money.

 

Oh sorry my bad... I looked at those X's and it looked just like Akra's style so I assumed so...

 

Add the ep exhaust with 100 cell cats. Then get a Cobb tune. Then intercoolers. The car will then be seriously fast. Just ask longboarder. Fast enough to break an axle.

 

Stock the drivetrain is remarkably stout. You've seen the 50th anniversary video with the guy doing 50 launches one after the other, right? Can't do that with a stock gtr.

 

haha yup I'm actually running the GIAC tune + meth injection, Champion intercoolers and BBI exhaust and I'm at 30psi mid-range and with rear MT drag radials at a nicely prepped strip it was too much for the little axles to handle. Don't know what I'm going to do with this car but if I ever try drag racing again I'm going to have to upgrade the rear axles (they are about $4grand installed).

 

Longboarder - 30psi on stock turbos?! That can't possibly be within the factory turbo's efficiency rating.

 

They are very big and very efficient turbochargers. I see 30psi in the mid-range...not at redline...there is a big difference and yes 30 would likely be outside their efficiency range at redline. I currently taper to 17-18psi at redline.


Once fueling is fixed, we will be lowering boost in the mid-range and increasing boost at redline, so a more flat boost curve.

 

Longboarder, do you have any Dynojet dyno's to post with boost plotted at the bottom?

 

No but you can kinda see my boost by RPM starting at the 1:30 mark in the vid below. My meth controller is also my boost guage in the sport chrono pod. Peaks at 30+ psi pretty early like 4,500 rpm and then rapidly drops to 17-18psi by redline. So I generally shift earlier than redline for max acceleration.