i'd like to introduce some engineering perspective here. for some background, i designed and tested some intakes on formula SAE cars and used to design subsonic compressible flow networks professionally. there are some things that confuse me about what this 'plenum' supposedly does, and some misconceptions that we can maybe clear up.

first, that IPD piece isn't really a plenum; it's a feed pipe to the two plenums on either side of it. second, the OEM plenum feed pipe on the M96 / M97 motors wasn't designed as a bullnose tee by accident, it was BY DESIGN. it is actually desirable for diffuse rather than laminar flow to supply an intake plenum.

the purpose of the actual plenums in these or any car is to stabilize the pressure at the intake runner heads so that each cylinder has the same supply pressure. a poorly designed intake will cause some cylinders to run rich & others to run lean. this can lead to all sorts of problems.

a well designed intake will ensure equal pressure at the runners. an extremely well designed intake can vary plenum size and runner length to take advantage of the harmonics that allow tuning of the intake system to a specific range of RPM's. porsche's varioram system does the former. varioram effectively increases the plenum size AND bridges two plenums into a single plenum. this allows the intake system to use harmonics to reduce disadvantages of static intake system designs. when designing an intake that does not vary runner length or plenum volume, there are compromises. one must choose whether one wants to use the intake to increase low end grunt or high end power, always sacrificing the other in the process. systems like varioram attempt to have it both ways.

to this point i've been talking about plenums and runners, but haven't really addressed the feed pipe. look at the IPD feed pipe. i believe the y-scoops will cause vortices to form INSIDE the two plenums that they feed. these vortices will occur near the center of each plenum, creating local low pressure areas just in front of the center cylinder in each plenum. in theory, this would cause the center cylinders on each bank to run lean and the outer two cylinders on each bank to run rich. this is not an improvement over the OEM design.

i haven't weighed in on this for awhile because fluid flows do funny things and it's not always easy to predict an outcome without running flow tests. the thing that always through me for a loop are the little pipes that seem to go across the inside of the IPD unit. i thought there might be some magic to these things, but was never really sure.

how 'bout you IPD guys chime in and explain the engineering thought behind this design? how have you verified the performance of the flow networks with and without your part installed in the network? have you actually used sensors in each runner to verify you've maintained or improved the OEM intake network's balance? what types of modeling have you done? any other tests besides dyno runs?

 

Sorry, but all your knowledge and logic won't work with most of these horseposers. They want to beleive. They want to read only those post that help them justify their expense.

However, great explaination. There are some here that believe in facts and not hype.

 

may be those who have the plenum should vote Yes or No on the perceived performance gain since there will never be enough satisfaction with dyno

 

not trying to knock the product at this point; simply acknowledging that there can be more to the story here. generally with this type of design, the product is proven with methods OTHER than a dyno during development. this is an opportunity for the IPD guys to weigh in and help us, as customers and potential customers, understand what went in to designing this product.

 

it seems at this point this product simply is not providing any peak HP gains as it says it will. You seriously do have to wonder how a $30 piece of pipe that costs you 1k is going to increase HP appreciably when it will cost you about 17K for the X51 power pack for Porsche to get you basically the same gain.

 

Seems to me I have seen flow charts showing increases but at this point Im wouldn't even begin to know where to look. People want someone else to tell them what to do here. Maybe those that really are interested need to try the part and figure it out for themselves. Thanks for you input. Gerry

 

Peak HP in this car is a waste on the street, things get illegal very quickly.

A nice fat mid-range and improved throttle response is great and what is needed on the street.

While my car has an improved peak, the midrange is significantly better than stock.

At least that is what my highly calibrated Butt Dyno is telling me.

If that is not good enough I am sure I can put it on a real dyno and make it tell me the same thing.

 

Insite986, your engineering perspective is greatly appreciated. I addressed 1999porsche911’s concerns with the IPD plenum in the “I was there, RSS Plenum Dyno Day” thread also in the 997 forum if you’re interested in reading that.

Most of the people here just want solid reliable power they can feel and enjoy, which is exactly what we offer. Customers feel the additional power because there is additional power. Almost 1000 IPD plenums have been sold with a full 100% money back guarantee and only 4 have been returned to date, not a bad track record. We wouldn’t sell the product if it didn’t deliver the performance that it does. We stand behind all of our products and we’ve gone above and beyond to prove that as well.But for all you internet engineers, I’ve consulted with our in house engineer who has worked for some very reputable Tuner and Motorsport teams. If you crave the “tech talk” then pull up a chair for this short novel that I’ve attached for your reading enjoyment.

One way to calculate an intake system is by using a differential equation. If you view the system as a spring-mass-damper (which, I repeat, is ONE way to solve intake geometry), your “m” (second derivative term) is the “force” of the air which relates to its mass and velocity, which is what the plenum serves to alter. Your first derivative “c” term is a function of the damping effect, which is set by the density and viscosity of the air. Then the “k” term is the spring effect, which relates to the runner length and diameter. Lastly as an inhomogeneous equation because the forcing function (aka piston) is going to put varying demands on the air traveling through the system because an engine operating in steady state isn’t too useful for racing.

Another theory I’ve found on intake geometry is by using Resonance. This relies on the pressure exerted on the air volume in the plenum by the back of the intake valve. The effect of this can be seen and tuned (especially with the use of a resonance flap, as seen in many Porsche engines) with the plenum geometry. Porsche seems to be very fond of this method. Again, I’ve personally spent hours on an engine dyno tuning the resonance flap trying to move the power band and gain peak power. So you’re using pressure to increase volumetric efficiency and gain peak power, not volume. But they are related, which brings me to the next theory.The claim on the IPD intake plenum is to reduce the headloss at the diverter section of the intake plenum (as seen in the patent filed years ago). V^2/2 + gh + P/rho = constant. So pressure relates to velocity. And since velocity relates to flow rate, for the same amount of time and cross sectional area, for a higher velocity, you got more volume. Compressible flow is a very complex subject, and it sounds like you are an expert, but I found in my studies in the University along with my personal testing that each application is very specific and unless you’re working for Ricardo there’s no way to make generalizations about flow characteristics.

Your concern of leaning out cylinders is very valid. This could easily be logged using individual EGTs. Frankly we have lots of dyno data that shows that the plenum picks up significant power across the powerband, which would dispel any fear of vortices forming (which personally I’m having a hard time visualizing). In every motorsports application I’ve used we tune individual EGTs using a cylinder dependent multiplier on the injector. For instance if bank 2 (cyl 4-6) is running rich you can lean out just that bank, or in more complex software you can tune individual cylinders to even out EGTs. No intake geometry at any level is perfect. Further tuning with a high end ECU I’m sure would net even more power! But the IPD plenum was designed to be a good “bang for the buck” and when you start talking about adding a $7k standalone ECU with custom dyno tune to level EGTs for the nth degree of performance, the plenum starts to lose its value.

To say that the IPD plenum is better then the OE unit in EVERY way is simply not true. Porsche has deep pockets and lots of resources that any tuner company would kill to have. But Porsche has many obstacles that aftermarket doesn’t have (sound requirements, smog, local vendors/manufacturing, cost, cost, cost). The plenum is very difficult to manufacture and even though the 997 is a very expensive car, adding a ~$1000 dollar plenum to the cost of each car would not be easy. Our casting process is time intensive and trying to make the plenum with a plastic injection machine like the factory would require a complex double slide mold with some interesting shapes. The factory has to compromise in some ways which is where aftermarket takes the reigns and offers the customer a unique sound, shift in the powerband, and every once in a while some more power. Think about aftermarket exhaust, which nobody brings up. There’s no way Porsche could ever market Cargraphic straight pipes on their GT3 RS, but having heard them in person… they really should. It picks up power, sounds better (to the enthusiast), weighs less, etc. But its simply too loud to sell in dealerships.

Again, thank you for taking the time to read this post. Personally I like putting my theories and studies up to the test. I’m always open for improvement! But I’m never content saying “OE always knows best.”

 

I don't know about you guys but here are a couple of damn good looking 997 dynos from the IPD Plenum Dyno Day. No dyno manipulations, No hype, No BS, just public dyno testing that proves the IPD plenum is the single best performance mod you can install on a late model Porsche. The gains are from beginning to end and the greatest gains are realized where is matters most, in the mid range. Enjoy!

 

Love the engineering response. Well played!

 

RSSGREG -

the post is appreciated. for the laymen, he's talking about a lot of different things here. when a valve opens, there's a push of air into the cylinder. when the valve closes, there's a push back. you can think of this like a slinky with a pulse travelling back and forth across it. the idea is to design the system so that there's a 'push' of air at the intake valve as it opens. this is sort of the reverse of the scavenging effect produced by well designed headers (they create vacuum and 'suck' exaust out of the head when the ex valves open). porsche's varioram system is designed to allow enhanced harmonic tuning at both low RPM's and high RPM's.

IPD claims reduced headloss at the tee entering the plenums. this is probably true; a bullnose tee (OEM design) causes significant velocity loss. the equation provided can be reduced to P + 1/2 dv^2 = constant since the tee lies in a single horizontal plane. this equation, though (bernoulli's equation) doesn't apply very well to non-newtonian / viscid flow. in this case, the velocities are great enough to warrant simulation vs. simple kinematic differentials to determine outcome. this type of calculation is even less usefull once flow becomes laminar. there are of course variants of this equation that allow for compressible flow & thermo fluid properties, but they are only good for point evaluation across the flow cross-section. this is where CFD is useful.

it is precisely becasuse all of this is so complicated that i was curious as to the design & testing methods used in development of this piece. i do understand that running multiple EGTs (or on the flip side,monitoring pressure at each runner) is not feasible to run IN EVERY CAR, but i should think this would have been part of the development process. afterall, fluid dynamics can be a freaky subject. it IS possible, afterall, to experience an increase in overall power while disrupting the OEM balance of the system. if there were a lean cylinder in each bank, this could lead to increased wear and problems down the line. this would be an extreme case, but it IS possible. what was done to verify network balance following introductio of this part to the system?

note: i made an error in my earlier post. when speaking about the possible vorteces, i indicated the center cylinder would run lean and the outer cylinders would run rich. this is backward. the center cylinder would run RICH and the outer cylinders would run lean. come to think of it, this could explain a power gain. the cars run a little rich from the factory as i understand it. correct me if i'm wrong, but most of the ECU tuning actually leans the car out overall. if this is the case, could it be that the IPD unit leans out four of the cylinders & results in a power gain? just a question....

come to think of it, that last explanation could explain why some cars see a gain and other don't. have we done enough dynos to get a correlation of ambient conditions yet? where were all of the INCREASES dynoed vs. where were the decreases dynoed? elevation, relative humidity, etc? it's possible that the IPD unit exploits an ECU programming shortcoming in certain ambient conditions. i really do think that if there are gains anywhere, they are NOT a result of improved flow but are the result of leaning out some cylinders more or less by accident.

 

There's no doubt in my mind the plenum makes real nice gains on the Turbo, I couldnt be happier w/ mine.

IMO it's most reliable, best bang for the buck, performance part you can buy.

As for the people that ask - 'Yeah but then why didnt Porsche manufacturer the part?' -
Porsche could probably make every single part in the car better given the sky's the limit approach but they want to sell cars at a nice profit. Anyone ever take off & handle the stock Turbo exhaust? You think that's the best Porsche can do? The Turbo could have had rear LED's from the start too but you know the deal.

Back to the plenum - It's interesting to see the results on N/A cars though.

This from european car "PROVEN"

 

Thank you Rteam. And so it goes. As it stands, I would buy headers from AWE and another plenum from RSS without blinking an eye. Gerry

 

Good gawd almighty! Talk about beating a dead horse. Fascinating engineering discussion, I think a flux capacitor should have been mentioned somewhere in the equation though.

Bottom line, you pay your money and you take your chances. Seems like the dyno shows power, now all we need is some track time to validate thoose gains and I'd say case closed...................Please!

 

So, no one but me sees the flaw in the PROVEN dyno comparison? It is really quite obvious and proves my point that resetting the ECU is where the majority of power is coming from.