Plenum vs. Cold Air Intake - what's the difference?
 

Hey guys,

I apologize for the silly question - what's the difference between say an IPD Plenum and a EVOMS Intake. Is the IPD Plenum an intake or something different?

Hey,
No worries, but you may do yourself a favor and save a lot of grief from some of the saltier folks here, and do several thorough searches on each, as each has been thoroughly dissected. At my own peril I'll try to be helpful. If I hit the mark, go ahead and note it with "reputation" points.

In brief:

-Cold Air Intake: all of our cars take in air (on a 997 it is taken in through the rear decklid and snorkle underneath which gets filtered and becomes available for use in the engine as part of any standard 4 stroke compression engine. The cooler the intake air, the better- has to do with charge temperatures, etc., I'll leave the how and why to others, or to you via searches either here or on Bing.com (the new Google). A so-called "Cold Air Intake Kit" is an aftermarket product, easily swapped for the factory unit. The factory unit is very, very good. Porsche doesn't leave a lot on the table for normally aspirated models (non-forced induction, ie, Turbos). An aftermarket kit, from suppliers such as Evolution Motorsport et al aim to bring more cool air into the engine, and do so faster. Again, the more cool air the better, especially if delivered faster. There are many manufacturers of these "kits". Do your own research and make a choice. I have the Evolution Motorsports kit (EVOMS), and am very happy. Again, search and learn.

-Plenum: know much about your P-car? Air comes down the roof, into the fins of the rear decklid, and into the snorkel underneath, then gets filtered, etc. and ultimately passes a purity sensor (Mass Air Sensor = MAS), then through the throttle body, then the PLENUM, then into each side of the flat 6 engine. The Plenum you are asking about, on the 997, is a black plastic "T" shaped unit which routes air into each side of the 2 flat 3's. The reality with a T is the hard stop at the top, with a dramatic left and right. The aftermarket plenum is more like a Y, where air is theoretically routed both left and right more fluidly, with as little turbulence or drama as possible, resulting (again theoretically) in more cool air getting into the engine, faster.

Disclaimer: I state no opinions on this stuff. I've got both the EVOMS cold air intake and the IPD/ RSS Plenum on my 997S, and I won't take them off. But there is a LOT of disagreement and angst around each topic. You've opened a can of worms. Good luck, and when you speak of me, speak kindly.
CATTMAN

Cold Air is denser, many turbo charged cars have intercoolers so that they can cool the hot exhaust gases.

Couple of minor corrections/additions:
The intercooler is in place to cool the air that gets heated via compression by the turbos. That is, when air of a given temperature is compressed (i.e. downstream of the turbo), that same energy is conserved and so the air temperature must rise. The intercooler lowers the temperature of the post-turbo intake air so that safe and efficient combustion is possible.
Re the MAF, it is literally an air mass sensor. A very clever device introduced a while back designed to try to inform the electronic fuel injection computer of the exact mass of air that is flowing through the intake system. It's a bit tricky to take in to account temperature and density and the prior designs of flaps and things just didn't work well enough to drive optimal performance. I believe MAF designs work by measuring the current required to maintain a constant temperature of a filament on the surface of the MAF. As the air flows over the filament it is cooled and the variable cooling (governed by air temperature, density, flow rate) can be converted to air mass. Very accurate, no moving parts and finicky enough to generate CEL's if the MAF/filament surface become compromised by oil (from some air filters) or other ick, that give odd or false readings.

Thanks for the help guys. Much appreciated!

EVOMS Intake or X51 intake add (small) HP the NON porsche Plenum does not. get an EVOMS Intake Do not waist your money on a plenum. Like i said in many posts. I will bring my car in. Dyno before and after the Plenum. show me the HP gain. NOT a BIG dip in the HP curve.

the 996 and 997 are cold air intake stock. :D

One more small observation: in years gone past the engine intake system generally sourced it's air from the engine bay itself. Even so called performance cars did and so as the engine heated up so did the air being drawn into the engine. Like the 356 below.

For all the reasons others have stated this was not a good idea and fitting a cold air intake, even a relatively simple one, would generally yield obvious and cheap horsepower, particularly when you wanted it like on the track.

While some manufacturers made attempts to address the issue, it really wasn't until emission laws were tightened up and every day cars moved from carbs to injection that it became more common. I guess they wanted to control all parameters more tightly and we started seeing properly designed systems integrated into the car body itself.

These days race teams in many categories regard the design of their intakes as protected IP, being one of the few area's where they can gain a significant advantage in tightly regulated series. On road cars most cars now have very good systems out of the box.

Yes, the intercooler chills the compressed intake air, generated by the hot exhaust gasses spooling the turbos. But cold air intake, though useful, can't compensate for the elevated temperatures that pressurization induces. Thus the need for the intercooler regardless of the initial temp of the intake air.

Close but.....the intercoolers cool the intake air, which is heated up from being compressed in the turbo before being ingested by the engine. this results in a cooler thus denser air entering the combustion chamber.

CAI is a general term for air intake that isolates outside air from inside engine compartment air. As other folks stated - all Porsches do have pretty good stock CAI.
EVOMS or similar cone filter systems feature vortex design of air intake with cone filters that provides less restrictive air flow by expense of smaller filter and dirtier air.

So easiest way to upgrade air intake is not to put EVOMS but simply put less restrictive filter - K&N or BMC oiled filters into stock airbox.

Plenum replacement IMHO makes most improvements on forced air systems. In NA cars where engine sucks in air plenum is not really doing much but RSS design may give some theoretical benefit as its shape should provide a bit less restrictive flow, but without making mods to your exhaust that will not be really justified. Plus, as it was stated here, this theoretical less restrictive plenum benefit wasn`t ever really confirmed by anyone.
If you plan on putting aftermarket full exhaust (or at least sport 200 cell cats) then perhaps it can make sense to work on air intake, but not other way around, IMHO. I honestly find price of $900 for a such a simple piece of pipe as plenum is highly ridiculous. if it would cost $250 - I would get it on my car just out of general curiosity. For $900 - they can keep it for yourselves.

Very well said. the best intake is the X51. two big filters. more surface area is good.
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Interesting thread and here is my 2 cents for you...I was at BBi Dyno Day on Saturday and they installed a IPD plenum on a '04 X51 package. Basline dyno read 299rwhp and after plenum installed showed 314rwhp. You can easily see the gain there, not to mention there was actually more gain at different RPM levels. They will soon post the graph for everyone to see. IMO, it's one the best mods and with money back gaurantee. You should call RSS and discuss this plan with them. I have not seen any failures on this....and take if from me I race cars and have nothing to do with sales. Cheers

No fense here but unless you have a dyno done DON'T suggest anything:confused: That's not how it's done in the real world:cool: Get your dyno done with baseline and after then make your suggestions:)

Yeah, but idea of cutting new hole for second intake in my car scares me.