minthral

My PDK 2017 C4S (no powerkit) seems to readily boost to 5 PSI at low RPMs, slowly climb to 12-14 PSI along with RPMs up to 5k, but then as you go to redline it stays 11-13 and slowly drops. I'm trying to figure out whats normal and if there is something wrong. There are no codes, car feels quick, but I have no idea is it supposed to be quicker...I normally don't redline and stick to mid RPM range unless passing.

The car has all perf options including sports chrono and I read that the S model is supposed to boost to 16 PSI, so that's the number I'm looking for in the boost gauge. I recall seeing 16+ for a split second, but that seems to happen I'm getting off the throttle quickly near redline instead of continuing to rev out at which point its slowly dropping to 11. Maybe first gear and hard acceleration I might have seen 16, but normally I'm more focused on 2nd or 3rd gear redline because what's used when passing really fast. I think 6 months ago during summer I might have seen 16 at higher RPMs, but not entirely sure.

I drive around at 500-700 altitude and use shell premium 93 gas.

kuma1416

I have a 2017 C4S with the Powerkit. At redline I will get 16 PSI pretty consistently. I can't remember seeing it go higher than that. I don't see it dropping after hitting 11-13 like you describe. I always use 91 EtOH -free gas. (No 93 avail where I live)

minthral

Can't figure out how to upload a video here...

Here is a video showing GTS. Its going from 1.2 (17.5) bar and down to 1.0 (14.5 PSI) bar at redline. Similar behavior I see except on mine is peaking up to ~13-14 at 5K+ and then near redline drop off to 11 (maybe... sometimes its 14 longer). I don't see 16 though.


Another video its more consistent 1.2 though...


Can't find anything for S, T, or base car.

minthral

Maybe GTS does 16 PSI and S does 14 PSI? Base 12?

Psorcery

This has been discussed a zillion times. Try searching the 991 section.

Time to trade in for something more millennial.

minthral

Yes I searched and don't see a definitive answer. If you want to try help, go ahead otherwise go grumbling somewhere else.


Ain't no one got time for that.

Ski Porsche

I have a .2 C4S and live in the mountains, typically driving at 4,400'-6,500' feet of elevation. I routinely see 16psi and sometimes, momentarily, 17psi. I have headers and sport cats, but regularly saw 16psi before installing them. Your numbers seem low. Maybe have your service guys have a look.

minthral

Mind recording a clip showing that so that I forward to my dealer? Mine wont go to 16.. 14 at best.

It could have something to do with colder/denser winter air and lower elevation. Not sure.

Ryan52589

I have a Cobb AP but I was having boost issues, believed it to be a vacuum leak for the longest time that nobody could seem to find after searching for months. Turned out the factory catalytic converter on passenger side was clogging with oil, after moving to bypass pipes (or sport cats if you prefer) the car no longer has any low boost symptoms. Maybe do a catalytic converter test? Just a thought.

minthral

All my research states that it should be boosting to 16. I guess I'll pursue this with dealer.

If anyone has any other ideas I'd appreciate it. I know that 6 months go during hot summers it was boosting to 16 but now during winter its not. I guess I'm trying to figure out if its winter blend/denser air etc.

spdracerut

my guess is that the car is fine. There are built in torque targets that the Ecu tries to hit. With colder and denser air, it requires less boost to make the same torque.

Ski Porsche

Aatish

Base is 12, S is 14, GTS is 16.

Bill_76

Aatish

hmmmmm.

What's the identifier for the reading?
There's a couple pressures related to boost; the true boost value is a sum of these values. Usually ambient and pre throttle.