Do you have any pics or can you direct me to a thread about this? Thanks

 

Question - with the 997 vacuum pump, can you remove the Venturi and line to the top of the plenum?

This would simplify the check valve setup and remove an area that can leak boost.

 

You remove the stock vacuum line that connects to the check valve at the throttle body and you put a vacuum cap on the nipple at the throttle body.

 

BTW, the 991 GT3 engine has an electric vacuum pump. It's located (looking from rear) behind the plenum on the LH side of the engine, beside the oil tank.

How do I know? Well, I just today got an oppoturnity to touch a r'n'r'd engine bound back to Stuttgart. Looked just like new one...mostly because it was, barely driven at all. Panamera's and Cayenne's also use electric vacuum pumps.

 

Slightly, but just slightly off topic, from AfterSales Training / Suspension, Brakes & Alignment:

Vacuum Brake Force Booster

A vacuum-assisted brake force booster is installed to allow
short brake pedal travel with low effort, without impairing
pedal feel. The booster applies a portion of engine
vacuum (approx. 0.5 bar) over a large surface area to
produce the required assist.

Electric Vacuum Pump (Cayenne Turbo)

On the Cayenne Turbo, an electric vacuum pump is
installed to improve brake boost. It is located in the engine
compartment on the right strut tower under the styled
cover. Under engine operating conditions with reduced
vacuum supply (e.g. catalytic converter heating following a
cold start, parking maneuvers, driving at high altitudes),
the vacuum pump is activated by the DME control module.

The DME control module uses a pressure sensor in the
vacuum line from the brake booster and activates the
vacuum pump, as required. Depending on the current
ambient pressure, for example at 1000 mbar (14.5 psi)
ambient pressure, the pump is switched on at a brake
booster pressure of around 500 mbar (7.25 psi) and
switched off again at about 300 mbar. (4.35 psi) On time
for normal operation without brake use is about 7 to 10
seconds. At high altitudes the switch-on point is lowered.
A quick test to diagnose the pump and the pressure
sensor can be carried out using the PIWIS Tester.

Mechanical Vacuum Pump
(911 Carrera 997 & Boxster/Cayman (987)

A mechanical vacuum pump is installed on the engine in
911 Carrera/S (997), Boxster/S (987) and Cayman S
(987) models. This pump provides a high and constant
level of vacuum supply and subsequent effective brake
boost even in unfavorable conditions, e.g. low air pressure
at high altitudes, and in highly dynamic driving involving a
high proportion of full-load operation, e.g. on race tracks.
This pump is powered by the exhaust camshaft of the
right-hand cylinder bank in connection with the oil extraction
pump of the right-hand cylinder head.

Unfortunately it's not mentioned what's "high level of vacuum" and how this "constant" level is regulated...

 

Bingo. This is exactly where I saw the shortcomings of the 996 vacuum system: high altitude (I live at 5200' with summer track density altitudes approaching 10000'), full load operation, e.g. on race track. There was a lack of a stable vacuum which did not inspire confidence in the brakes. This is now remedied by the cam driven pump. Good read..

 

I was thinking about going to electric vacuum pump, but that document made me think that again. Electric pumps seem to let the vacuum fluctuate between for example that 300-500 mbar. That might have an effect to the pedal feel. OTH the mechanical pump, without any electrical control, has to keep the vacuum in some very simple way, ie with somekind of preset valve. Thus the vacuum doesnt vary at all. Mechanical pump robs some power though. I doubt there's neither any significant weight difference.

Now another thing.
GT3 (NA engines) have a different part number for the tandempumpe than turbo engines. Other cylinder bank's fuel pump has the same difference. That made me think that both pumps (NA & turbo) most likely have the same vacuum unit, but the difference lies on oil pump's side. Maybe camshaft's ends are different? Anyone?

 

Pete,
The pump mounting arrangement on the oil side is identical on both the GT3 and GT2/TT pumps. My shop and I looked at both and the only difference we were able to arrive on is the fact that the GT3 pump may be geared slightly differently due to the higher redline of the GT3 motor compared to the GT2/TT motor. Visually both pumps are identical.

As a side note, I ran another two track days with the new vacuum pump set up and the brakes are simply phenomenal.

 

Thanks!

More reading: http://www.kspg.com/fileadmin/media/.../ppt_EVP_e.pdf

 

new part number for this is 99710702273

This is the gt2 version. best price as of 4/5/19 is about $1100. Yikes.

 

The GT2 pump failed on me after 3 seasons or about 10k miles. I don’t think it was designed for the higher rpm I was running. I am now using the GT3 version of the pump which I would recommend over the GT2 version if running well over 7k . The downside is that the GT3 version is more expensive still at $1700 but must be geared internally different for the higher rpm a GT3 engine sees.

 

99710702291 in case anyone is looking for the gt3 part number.

 

I was driving around today and was just thinking to myself "man these brakes have no bite and they require a lot of pedal." It's interesting because when I upgraded them I thought they was so much better than stock, but now I'm used to it and they really aren't that great (350/350, pagid yellows, fluids, lines, fresh calipers). The improved vacuum definitely makes sense, although I'd love to see a simpler/more affordable option such as a vacuum canister like Rufian mentioned. Seems like it would be easy and cheap to do, and there's plenty of space up by the brake booster to install it. Plus it would be less potential oil leaks and failures from the cam driven pump.

 

I'm going to the 997gt3 master cylinder. Only will do this if I'm really not happy.

 

Just a thought here but on the 997t/gt2/3 the first journal on the exhaust cam is drilled through to line up with the oil port to that journal. The cam has a plug in it and uses a shorter cam bolt that has a hole through its center that feeds oil into the scavenge/vacuum pump to lube it. This could have caused your failure. The pump runs off the cams so it is running half the crank speed. 997T factory redline is 6750 and gt3 is 8400 that is a difference of 825 rpm. I know a few 997 turbos with there original pump that rev to 8k and better. I and interested in the gt3 pump as the cup cars do not use them so I have never seen one I am also interested in the 991 electric pump more so.