roddylennox

32krazy!

use a mityvac silverline and test each gate to see what the cracking pressure is. then test at the n75 valve to see if each side opens at the same time

roddylennox

Thank you. Is this what OPCs and Porsche specialists do at each service or do they just road test the car and read the boost display on the dash?

pfbz

First test that the actuator rods can manually move through full range of motion with your hands, then hook up a pressure tester and apply some pressure and see what the cracking pressure and fully open pressure is.

I used this pressure tester, cheap on Amazon and it worked great for testing all sorts of Turbo hardware.

www.amazon.com/gp/product/B01JRRIEBI





No, i don't think most Porsche technicians check this on any routine service. Nor will they normally do any pressure testing to look for blown check valves, unless there is a trouble code or complaint they are hunting down.

The turbo's have lots of headroom, and when building max boost, waste gates are tricked into not bleeding pressure with the N75 valve, so an improperly set waste gate or bad check valve often goes unnoticed. Now if the diaphragm was completely torn, I think it would show up on the boost gauge or with a check code readily?

Kevin

Folks, the 997TT and 991TT do not have wastegates. Boost control is handled by a electric servo drive motor with a mechanical rod linkage connected to a variable pitch nozzle. The nozzle ring assy has 11 blades which direct the exhaust gas towards the turbine wheel. The pitch of these 11 blades increase or decrease the exhaust flow like a gate valve.

To inspect, get under your engine and move the linkage on each turbocharger. There is a factory TSB that instructs Techs to lubricate the linkage ball ends to prevent seizure. One should address this each oil change or at least once a year.

TT Surgeon

Nate Tempest

This thread, especially the link in the last post, could be useful: http://911uk.com/viewtopic.php?p=738500

tinkerbill

I found this on the forum while researching a boost question on my 2012 TTS. May help, may not
Originally Posted by Evolution MotorSports
Hopefully I can shed some light on the boost discrepancies that each model year cars have. For the 997.1 turbo and the 997.2 turbo, the boost gauge displays a "programmed value" and does not correlate to the actual manifold pressure. Porsche started this "programmed" boost gauge after having many customer service questions on the 996TT which showed "actual boost" (not programed).

The 996TT was reading the actual and accurate boost pressure in the Y-pipe before the throttle body. The problem was that when the throttle body closed rapidly, the boost gauge would show an arbitrarily high boost reading on the gauge due to the high pressure in the Y-pipe before the boost was recirculated by the diverter valves. Some customers would complain on stock vehicles that they were seeing 1.6 bar of boost when they were modulating in and out of boost.

When the 997.1TT was released in 2007, this was the end of a real boost gauge that showed an accurate reading It is programed to show 14psi (1.0 bar) in non sport mode and 18psi (1.22 bar) in sport mode. Although the car may or may bot be making this boost level, this is what the gauge will read. In some of our software calibrations, we will run 20-23 PSI of boost in both sport and non sport mode and the OEM boost gauge will only display 14psi (1.0 bar) in non sport mode and 18psi (1.22 bar) in sport mode.

For the 997.2TT, this is again a programmed boost gauge. It has very little to do with the actual boost pressure in the manifold. Since the 997.2TT has a TQ based ECU, boost pressure is only related to the programmed TQ value. If you were to put an external boost gauge on a 997.2TT, stock or modified, you would be surprised how the boost curve actually looks compared to what the OEM boost gauge is displaying. Typically, the boost will spike up at 14 psi, drop to 10 psi in the mid range, then slowly climb up to about 12 psi by redline.

Bottom line, the only way to accurately monitor and see the actual boost on the 997.1TT and 997.2TT is to install an external manifold pressure boost gauge. I hope this helps with some of the questions.