Details on how does the OEM Plenum work?

For the Gen 1's, I know there is a vacuum activated baffle flap in the OEM Plenum... - At what point does it open and close, at 3,000 RPM? - Does it open/close at any other RPM points ? - Does it open/close based on RPM only or both RPM and Load? Thanks.

I dont think its rpm based. If its vacuum actuated it will be a combo of rpm and throttle position. Think of it more as Power Demand activated.

The vacuum actuation is controlled by the DME via solenoid valves so it could be on rpm alone. I don't think this is the case. It's probably rpm and throttle position but I don't know for sure. This would make it load based like flybot stated but there's nothing mechanical about the activation.

The flap in the distribution pipe ( Porsche 's term) is actuated by rpm. At low RPM it is closed so the engine runs essentially as two independent 3-cylinder engines. This is supposed to improve torque. The actual rpm of opening of the flap seems to depend on the model type. Boxster (987) – The distribution pipe flap is opened in the two rpm ranges from 3100 to 5000 rpm and from 5600 to 7200 rpm. Boxster S (987) – The distribution pipe flap is opened in the two rpm ranges from 3500 to 4700 rpm and from 5400 to 7200 rpm. Another source for the Cayman S states The distribution pipe flap is opened in the two rpm ranges from 3500 to 4900 rpm and from 5200 to 7300 rpm. -Todd

tholyoak, is bang on the money, its also a different setting for the stndard model versus the S. The purpose is two fold, first to improve torque but also to improve emissions. I'm considering working on some development work to see what effect changing the opening and closing points have on power and torque. The Cayman / Boxster is the only porsche model to have two distribution flaps on the inlet manifolds. The solenoid works on vacuum to actuate the flap but is controlled by the DME , just like the PSE which uses the same solenoid part number !

I figure your objective is to optimize torque only . Think I read somewhere that newer models have 3 flaps now??

I vote for 6 velocity stacks with 6 flaps all sticking up out of the back window!

"ranges from 3500 to 4900 rpm and from 5200 to 7300 rpm." Interesting.. twice? When does the Variocam switch on the Cayman S ? The intake Flap is certainly not a new concept, it started on 928S4 then 964/ 993. The flap is suppose to effectively change the 'length' of the air path. Air 'pulses' in waves as the intake valves open and close. The idea is to time a high pressure wave as the intake valve opens. Its more effective at low RPM as the pulses rates are lower (thus low end torque). At high RPM you just want air in fast (all flaps open - shorter intake runners) Not sure why the Cayman S open twice? Unless there are two flaps? 3 stage approach.

The 996 and earlier models use a single "resonance" flap between the two manifolds. The 987 cayman / boxster are unique I beleive in that the tube after the throttle body is partitioned internally and also posesses a second flap at the end. The purpose of the split intake tract after the TB and second flap married to the position of the throttle body is to improve low end torque. It would be interesting to overlay the 996 3.4 against a cayman 3.4 or boxster 3.2 to see how significant the modification actually is. Its more than possible the actuation of the two flaps is purposely controlled to reduce mid range torque . Certainly the throttle body flap isnt positioned ideally as it restricts air flow, this is a different situation in the 3.2 Boxster where it sits in line rather than across the air path. The two flaps work independently of each other as one is in each of the two connecting bridges between the left and right intake manifolds. Variocam adjusts the cam timing , variocam "plus" changes the cam profile by adding additional lift. I beleive the "plus" element kicks in above 2800 rpm , I was told this was to ensure the emissions are kept passable in the US and ensure the fuel economy at motorway cruising speeds in high gear is maximised.

So is there an upgraded plenium for the 987.1 motors that improve low/mid range torque and hp like the gen 2 option. Would this require a ECU flash as well?

Oh yeah... Softronic , a P-9 sponsor, makes a plenum and software setup. I can tell you that I love the one in my car. They work better in combo with a free-breathing exhaust . i have a conservative cat-back system. It does eliminate two of the 4 cats in the exhaust , so back pressure is less. Whatever, it's nicer now. There is another setup... IPD plenum and GIAC software, The IPD looks a little more aerodynamic than the GT3 plenum, but isn't an OEM part. NEITHER OF THESE PLENUMS has any flapper valves in it. The response is more linear and intuitive. If you don't want an aftermarket exhaust or a plenum, Softronics and probably GIAC make a software only package. I've heard good things about the Softronic one. Not heard much on GIAC but I'm sure there are lots of posts somewhere. :cheers:

Does anyone have any experience of this vacuum-actuated flap system failing in a Cayman ? Thanks

I don't have experience with it failing, but I have experimented with it extensively and quantified it's effect. I believe they both fail open (which is their state above ~5300 RPM) but either way it effects volumetric efficiency, and in this state low end torque loss would be noticeable. If both valves were to fail closed (get stuck) the engine power loss is quite noticeable at 4000 RPM and above. If one or the other fails you get some result in between not as easy to describe. All said it doesn't hurt anything if they fail but you may notice lack of torque/power and possibly lower fuel economy and if I was forced to choose I would probably leave them both open.

When the PSE is switched it seems to activate them also

Reviving this old thread... I recently removed the intake distributor tube on my 987.1 CS. During the process I must have broken something. The vacuum operated actuator for the plenum flap is now disconnected from the flap, and I see no obvious way to reconnect it. I have ordered a new distributor tube (PN: 98711011601), but I'm wondering if I need a vacuum actuator too (PN:98711046200). I also wonder how the arm from the actuator is supposed to connect to the plenum flap. If I can't figure it out, will my car run ok with the flap stuck open and the vacuum line(s) plugged?

Just to bring closure...I plugged the vacuum line to the flap actuator, and filled the hole in the plenum (intake distributor tube) with a vacuum plug and silicone. The car ran well and idled smoothly for 6 autocross runs, but the silicone did not hold. I have since received and installed the new plenum/intake distributor (PN: 98711011601), and the car runs great again. The part comes with the vacuum actuator attached. I think the Parts diagram is either outdated, or designed to work for several models.