Alex (UK)

Hi guys

I believe the 997 Turbo is supposed to get to 1.2 bar boost pressure with Sport Mode and overboost (1.0bar in Normal Mode). The Drivers Guide does show a pic of 1.2 bar with overboost arrow.

Anyway, recently I found a quiet stip of straight dry road, and had a play with the boost figures. I only ever use 99 octane Shell vPower fuel.

Normal Mode
If I put the car in 6th gear, then I can get 0.9 bar for about 1 sec, then it drops to 0.8 bar and stays there.

Sport Mode
Again, in 6th gear, I can get to 1.1 bar for a split-sec with the overboost arrow showing, then it drops to a constant 1.0 bar.

I am wondering if the reasons a lot of the guys with manual cars that are seeing 1.2 bar is because they have reduced the exhaust back-pressure from switching to an aftermarket exhaust?!

Either that or newer Turbos are being tuned-down slightly compared to early factory productions?!

What do you think? I would interested to know what other 997 Turbo owners have seen.

TT Surgeon

I got 1.2 with the stock exhaust at times, but frequently with my fabspeeds.

Alex (UK)

As I just replied to Jason on Rennteam:

Hmmm

How long do you see 1.2 for? As long as you have your foot fully down on the gas pedal?

And do you see this in 6th gear or are other gears easier to replicate with?

I am just wondering if Porsche have deliberately restricted MY08 Turbos for some reason?!

TB993tt

The Motronic ECUs on these engines are looking at the mass of the air and comparing it to data in the program map the ECU will allow the boost to rise and fall to hit these target mass numbers. On a warm day the boost will tend to be higher since more air will be needed to hit the mass target.
When the weather is cooler like in the UK at the moment the ECU may ask for less boost to achieve the same target air mass hence you may only see 1.1bar now but 1.2 or even more in the summer.

The other thing which always has to be questioned is the accuracy of the boost gauge -I don't know how good the 997tt one is but typically 911tt boost gauges are pretty hit or miss on accuracy.

If you install a decent analogue boost gauge you will be able to watch how the ECU alters the boost constantly according to all the inputs it receives (if you are sad like me that is )

Alex (UK)

Great reply, thankyou!!

TB993tt

A pleasure

AAHTT

when my car was stock, it boosted 0.9 bars in normal mode between 2500 rpm or so, until 4000rpm, regardless of gear and regardless of temperature and with crappy 91 california octane.
In sport mode it would boost 1.2 bars all the time between 2500 and 4000 rpm especially in taller gears but also in lower gears and regardless of outside temp and then back to 0.9 beyond 4000 rpm or so.
Adding the aftermarket exhaust improved throttle response but had no effect on boost in my case. adding the ecu tune has a similar effect but the difference is that a tuned car will boost 1.2 bars all the way to redline.
Hope that helped.

whyb2nd

.9 stock mode and 1.2 between 2-4K in sport regardless of temp and altitude. I'm at 5,400ft and forced to use 91 octane.

DSUNNYM1

My car is a tip with a little over 2000 mi,,,,
the most i see in sport mode is A quick flash 1.0 ??

Hoping it will increase with more miles??


Any info??

Alex (UK)

I am thinking the factory are now setting boost to 0.8 bar for Normal mode and 1.0 bar for Sport Mode for all MY08 cars. I doubt MY08 cars will be slower than older models so maybe Porsche have made small improvements in other areas and then dialed down the Turbos to balance it out?!

Perhaps though it will get better after the car is more run in. This is more wishful thinking than anything else though .

What we need is someone with a MY08 Turbo to say whether thay can get 1.2 bar or not.

DSUNNYM1

+1

TB993tt

Alex, PLEASE, the boost you see is not an accurate reflection of how fast your car is (or anything else ) the ECU is reading the air mass in kg/hr and adjusting boost to suit, the factory are NOT "setting" any levels of boost, it doesn't work like that - unless as you (paranoidly...sp ) imply they may be depriving you of your full 480PS DIN.....
Boost on Motronically controlled Porsches is not neccessarily proportional to hp (when comparing one set of running conditions to another). There are Rlers running 1.2bar (on 993tts -older but same principal ECU) at peak power, managing about 470hp and others running high 500 hp at less than 1bar.....

If you are concerned that Porsche may be giving you less hp, get a GPS device and do some acceleration runs, missing hp is easily spotted, as you say it is possible (but unlikely) they can still make the 480PS power curve with less boost at DIN

Alex (UK)

Did a bit more playing today. Managed to spot the ellusive 1.2 bar at last - albeit only for 1 second or so.

Strange it doesn't stay for longer even if I kept the gas pedal flat on the floor.

Yogi911

Thread revival...see i actually searched. Haha

Anyway i did rss engine mounts last night. My first diy on the car
I taking all the intake stuff off made me a little nervous but i think i got it all back on there. The only connection that is "suspect" is the passenger side black accordion joint by the maf sensor post air filter pre turbo but it is secure.
Anyway have gone for some drives to make sure i didnt have any boost leaks. My car seems to be trailing boost off more than before but not by much. Maybe 1-2 psi. So if i over boost starting at 2k in sport mode 5/6 gear it hits 17 for a second (like 3k rpm) then down to 14. In 1-4 gear im not seeing over 14 and it trails off to 10 psi in 1-2 and 12 psi in 3-4 gear.
This summer it was usually 80-100 degs and last couple days its been 60-70 so the lower boost may be because of that. Generally car feels ok.
I just never noticed such low boost in 1-4 gears and it seemed like it held 16-17 psi until at least 4k rpm before and now only 2800-3k.
Thoughts?
What boost do you all usually see at redline in each gear on a 70 deg nice day. I am stock ecu.