I have a few basics of the 996TT boost system which are not clear to me. Tried to make my questions simple :

1. True / False : With pressure hoses off the actuators, you will always get EQUAL to or MORE boost, than if hoses connected back to the N75 valve ? (regardless of ECU tune).

2. True/False: A bad actuator valve assembly, could cause a WG not to close properly (overridding the spring trying to close it), leading to low boost ? is this sometimes called "sticking wastegates" ?

As I have a low boost problem, I disconnected the WG actuator hoses and (very carefully) test drove it. At WOT, no more or less boost than with them on, still low at 0.6 bar (non x50, ECU mapped) at max air flow rate. mut be an airleak then ?

Thanks for any views !!

 

Theortically if you disconnect the vacuum lines to the wastegates, the car should overboost since the wastegate will never crack open and all of the exhaust will pass through the turbine. It sounds like you may have a leak somewhere, or maybe the wastegates are stuck open which would explain why the turbos aren't making any more boost..

 

Do a boost leak test. If the car was running fine, don't mess with the wastegates yet. Much more likely to be a boost leak or a problem with your diverter valves. Is this car new to you?

 

If you unplug the electrical connector on the N75 valve you will be running WG spring regulated boost only. This is not gonna be much boost at all and will tell you if the issues is mechanical(WG or leak) or electrical(N75, MAP sensor etc).

 

Interesting essue i keep watching this to the end,thanks

 

As I prepare for my first 996TT purchase, I can't help but wonder about the intricacy of the turbo. I am a hands-on guy who prefers to work on my own cars (up to a point). I owned a non-Porsche turbo many years ago, is there any documentation available with exploded views etc. that discusses the specifics of these 996 turbos? Thanks.

 

thanks all. I am nearly sure with actuators off , that this is the maximum boost you can ever get, as WGs won't open in that scenario.

I am running my non x50 with actuator hoses off and seeing upto 0.9 bar at WOT. I believe this I should be upto 1.3 without hitting WOT (AT 1.3 I have plans to lift off throttle to save the engine).

I am inspecting the turbos and piping this weekend to see why so low a boost.

 

what are your mods and tune?

you shouldn't boost upto 1.3 bar with no fuel mods thats asking for troouble here man.

i know your trouble shooting but id bet that you ahve a nasty boost leak or your diverter valves are not fully closing.

pressure test look for markskis thread for the DIY

i cant remember off the top of my head but i think .6bar is stock boost level someone correct me if im wrong.

 

Spoke to turbo manufacturer and found out the wastegate on our KKK turbos are held closed puling against the incoming exhaust flow. There is NO built in protection with these turbos re automatically reducing boost if the actuators are not functioning. But if your wastegate arm is broken, the wastegate will open fully, as exhaust flows in the direction of it opening. the arms break a lot I hear (near heat source) and this is heat cycling of the rod, leading to hardening and then cracking.

It is possible the ECU will cut fuel if it senses too high a boost level, in same way as rev limiter. Our wastegates won't open without the actuator pulling it open againt the springs keeping the WG closed.

discconecting the actuators is of course very dangerous, as you can blow the motor due to effects of ooverboost.i would not recommend it , but did it v carefully. I am also hearing max boost uncontrolled is 1.7 to 2.0 bar for k16s. But I have strange fault, meaning 0.9 max at WOT with wastegates closed (no actuation pressure on). I wanted to know the source of the fault, and have found out it is mechanical. Boost builds quickly, but runs down with increasing airflow, so I suspect is one of the turbos WG not seated closed or possibly air leak which i cant hear anyway.

my mods are cargraphics, remap (UK), forge, air filter, stock K16.