Plenum upgrade "Real performance or Hype"?
 

Having read all the aftermarket claims, is this something worth the time and trouble?
The claims made are great, however I'm skeptical, seems like a miracle in a bottle kinda thing. Any thoughts?

Depends upon your perspective. Do they actually add power? The answer is yes, but not very much and only in RPM ranges the engine rarely sees.

There's been threads on the plenum chamber previously.. the upgraded throttle body would probably give better bang for the buck. when considering the cost of say the IPD plenum and a used larger bore throttle body (i think from the 996 though nobody quote me on that)

I have both the IPD and larger throttle body. It's an expensive mod. I would do it again if I had the need to. The parts alone don't help as much as the claims say. It isn't until you retune the car. Then you feel more improvement.

In short to get the improvement you have to tune and buy the parts.

I measured dyno gain for 996 throttle body and plenum
http://986forum.com/forums/performance-technical-chat/47555-tuned-modified-2000-boxster-s.html

^^^ This.

Opening up the intake might find a few ponies especially above 6k rpm. How much time will you actually spend above 6k rpm? Will it deliver faster lap times or only inflated peak dyno numbers? How much is that worth to you?

We use modified IPD arrangements on most Stage II engines. In my experience, until you add 400ccs, a point of compression, some real port work and etc , the gains are minimal.

I have seen stock engines make less power with them, back to back on the dyno.

Air air more air!

Just keep an eye your accu weather channel for wind direction and just hit those roads. With the wind in your back your boxster car will feel like having +20 more HP

.... well the 2.5 does anyway lol

I say Hype

It's all hype unless it's ...

Larger valves
Camshaft lifts valves higher and/or longer
Displacement is increased
Forced induction is added

To think a company like Porsche has "strangled" your engine by fitting a drastically inefficient intake and/or exhaust system is patently ridiculous.

Cheap fixes would be great, wouldn't they? But reality is it's pay to play.

I think that is exactly what they did, how else can a:

2.7L 986 have 217 HP, ~80 HP per liter
3.2L 986 have 250 HP, ~78 HP per liter
3.4L 996 have 300 HP, ~88 HP per liter

Looking another way, the additional .5 liters between the base and S Boxster yields only 33 additional HP, but the .2 Liter difference between a 996 with a 3.4 and a 3.2 S is 50HP?

I would like to be getting 88 HP per liter in my 3.2 S, that would be 282 HP :) I bet I could feel that :)

Agreed, they are not cheap, one example is to get the bigger intake (the piece that bolts onto the top of the engine that says "Porsche") in the Boxster you have to drop the engine down a little to clear the engine cover because it is taller on the 996. That's why a 996 engine transplant has to be mounted a little lower. Somebody on here has a really good thread and has done a lot of these mods but I can't think of their user name right now. If you search for threads on throttle bodies you will find him. Everytime I read his threads I get excited... but realistically I know those type of mods are beyond me...

They design and spec the components with an eye to cost but also to meet the design brief of the engine and car package. What's on the car is designed to give the car the power and characteristics they want to market and are perfectly fit for purpose. There is no need to design them any better or more efficient as that is not what was in the spec in the first place.

I understand that the IPD arrangement has the potential to direct and accelerate the intake air left and right giving more "authority" to the charge, but I have always been concerned that it would restrict acoustic pulses side to side (perhaps this is not a valid concern). Especially when the resonant flap in the cross tube is shut. One can see that the design has evolved with different types of relief holes through the "divider blade" perhaps to mitigate this very issue.

Just a guess:

The engine is drawing the intake air in and the divider could potentially disrupt side to side (one plenum feeding the other) cylinder filling in certain cases (engine rpm and flow rates).

It would look like this design would be much better suit to forced induction where bank to bank acoustics would be covered off by positive pressure before the divider blade

No, on an normal aspirated engine the short side radius is always where the greatest air speed and velocity will be found. On the flow bench, the long side can have a pitot tube introduced and you'll find no velocity, or a slight vacuum.

This is why I laugh when I look at the arrangement that some out of work practical Engineer did in his Garage, using a vacuum cleaner blower motor to blow over objects, in an attempt to design a component.

The short side is where the men are separated from the boys, and it doesn't mater what it looks like, all that matters occurs on the flow bench.

This is why I laugh when I look at the arrangement that some out of work practical Engineer did in his Garage, using a vacuum cleaner blower motor to blow over objects, in an attempt to design a component.

Ouch!

I think that is exactly what they did, how else can a:

2.7L 986 have 217 HP, ~80 HP per liter
3.2L 986 have 250 HP, ~78 HP per liter
3.4L 996 have 300 HP, ~88 HP per liter

I agree with this, and there is further evidence from the current 3.4 liter engines: 350HP in a 911, but only 315 in a Boxster S.

There's more to it than that... The 986 engine uses the same cams as the 5 chain, 3.4 996, they are even stamped as such right on the cam blanks.

The cylinder head ports and castings are also the same, BUT the 3.2 chambers are 3-4ccs smaller, for the smaller bore size.

4 valve engines respond aggressively to bore size increases, the 3mm difference in bore size between the 3.2 and the 3.4 is HUGE in regard to swept volume, and chamber filling. The entire intake system is different as well, as the 986 intake runners are longer and thinner and extend from the plenum chambers all the way to the cylinder heads without interruption. The 3.4 996 does not do this, at the 70% point it breaks away and changes to a more effective aluminum intake runner that bolts to the head.

The plenum areas are also larger.

We find huge gains with intake manipulation, but thats not meaning bolt on items-

Porsche knew that the engine in the Boxster was in the right place, and the engine needed a handicap to keep the performance differentials between the two cars so the 911 would remain the flagship.

Because of this, we have always been able to increase the percentage of power increase more with the 986 engine more than its 996 counterpart. Its not uncommon for us to produce 100HP more than stock from a 3.2S engine for a totally street able engine, on pump gas, with a red line that can be reduced 500RPM lower than stock.

Yes agreed but I am talking about bank to bank flow pulses over the divider blade where you see relief holes......normally that would be a dead area yes

Those holes are for lightening the casting, not performance. A pitot tube in that location will show zero air speed.

Thanks Guys, you've really given me great info. I think I'll just leave that alone. Don't really need more power, just have the itch to tinker with things. This is a mod I can live without. Reward vs effort isn't there

Absolutely waste of time and money.
I did put the 74 too and finally went to test the car.
Lost in every segment and I went from 223cv to 211cv.

http://986forum.com/forums/uploads02...1631898848.jpg