Valvefloat991

I am about to undertake a mild tune on my 2017 991.2 Carrera, by replacing the stock turbos with Carrera S units and upping the power and torque to roughly stock Carrera S levels. The shop doing the work suggests replacing the diverter valves at the same time, along with the air/oil separators.

Is this necessary with such a mild tune? How often do these components fail at well-below stock GTS power levels?

F355bob

with a tune alone you should be at stock GTS levels
A tune plus S turbos will give you that much more.
I replaced my diverter valves when I did a tune. Easy. Inexpensive and good insurance

enzotcat

If you're replacing the turbos, enough stuff comes off of the car that replacing the diverter valves is easy. The valves themselves are not super expensive, so it's really good insurance to do it. To answer the question directly - at stock power levels, they don't fail. There have, however, been some failures at higher than stock levels. If you're sticking to GTS or lower power levels, you should be fine, but most S tunes are more than stock GTS power.

DR911s

I much agree with enzocats's advice. I have a 2017 C2S and shortly after having the 4-year major service done at 27k miles, I installed an FVD Brombacher tune, and not long thereafter started getting fault codes indicating low boost and boost pressure deviation from setpoint value. I was at maximum seeing 12 - 13 psig on the dashboard boost gauge before I replaced the diverter valves with those from Flat 6 Motorsports. Thereafter I quickly see 17 psig on that dashboard boost gauge. Changing those diverter valves is one of those "while you're in there" jobs that should be done as preventative maintenance IMO.

Edit 3/24/24: IF my OEM stock diverter valves were functioning properly, I should have been seeing more than 13 psig on the dashboard boost gauge, probably 15 - 16 psig. At least one of them was leaking under "full boost command" conditions, and that also showed in slower relative acceleration performance of the car when on the OEM tune.

Valvefloat991

Thanks for the advice, but I do intend to stay below GTS power levels. I will be selecting my tune based on that restriction. I'm doing this because I live in the Denver area and often drive in the mountains, where pressure ratios can get sky high.

o if I don't exceed stock GTS power levels--or boost (18.25 psi)--do you think I need the atermarket diverter valves?

And what about the aftermarket air/oil separator?

enzotcat

You don't need them per se, but remember that if they do go bad you're going to incur more expense replacing them than if you just did them as part of changing the turbos. Like I say, it's more insurance than anything else. If you're on a tight budget, then go ahead and leave them out. Chances are you'll be OK. Speaking of tunes, which tune are you planning on using?

Meh. I don't have one and I track. Some people swear by them, but I just don't see the need.

4 Point 0

My GTS only had an OTS COBB stage 1 tune and I was doing a whilst I was in there, change. We were shocked to see one had already failed.

They are notorious for failure across many platforms, as the spring has to fight boost. Whereas aftermarket ones, boost helps keep them closed and they open off boost.

The former is setup to fail. Its only a matter of time.

AOS is also a when you get around to it. Which I haven’t done yet If you do regular track maintenance its less important.

MingusDew

They fail on stock motors. They fail faster at higher than stock boost levels, particularly with larger turbos running 20+ psi. Sooner or later you’ll be replacing them. The aftermarket units are pretty much same price as OEM, but the aftermarket ones will last longer on high hp cars and then are designed to be rebuilt at home (easy). If you already have the fascia off, it is about 30 min each side to remove the IC cage and replace the DV. Otherwise, you’ll have to remove the fascia to get at it, which isn’t difficult but does add a good 1.5-2 hr to the process (remove/reinstall)

spdracerut

If you ever hold a stock one in your hands and mess around with it, you'll notice it has a relatively flimsy rubber diaphragm. It will fail at some point.