Guys,
I have an untested mod idea we can try which may very well give us some extra power. Maybe someone is willing to try? Its simple and costs nothing.
Remove the stock plastic Plenum and take out the flap indicated in the picture.
Intake Theory ?
I was wondering if you found some new imfo about why the plenum mod works because on a post on the new IPD Plenum you were explaining how it did not work.
Now your suggestion is to do in part what the Plenum mod dose because you think it is a good idea.
I have the Plenum in my Cayman S and I can say it is a great idea and delivers outstanding performance gains not only due to the part you say should be removed but take a closer look and you will see the throttle body is moved much closer to the intake runners and this is also a good idea if you are intrested in improved throttle response and it might explain the reviews other members are giving on their Plenum installs or maybe not you know Ken has not dynoed it yet so we just don"t know.
Hello Elmo,
No don't get me wrong, I have nothing against it and I do expect there will be an improvement of some sort. We just need to qualify that amount.
I like to understand how things work seeing I am an Design Engineer, as well as a few other things. We need to consider any disadvantages to any mods, that's all. Don't we all? I would also like to see any mods independently tested. Theory wise I expect a drop in torque at the low end because the control flap is removed which would normally close at the low RPM to improve the resonance charge injection, however as there are many factors involved, its better to do the real tests and confirm such. Plus its likely that even if there is a drop we may not be worried about it esp if we gain at the mid to top end. In addition, possible resonance loss may be more countered by increased flow efficiency etc.
Re this mod. It should provide some improvement by reducing turbulence and improving air flow a bit. Wont be as good as the proper Plenum, but as it is a freebie why not try it. Anybody game? I bet this will be better than the "de-snork" mod.
I'd try it but never seem to have enough time to play.
Intake
Hi, 4X4
I can understand about finding the time. Its great to see engineer on the site. The company I own works with and contract manufactures for comercial and military areospace we also produce for advanced weapon systems (nothing real complicated like a car) So I do understand why you want test results to make your decision before purchase,but if you would like to give my judgement any weight I would tell you look at the RSS dyno it is an accurate description of the performance added.
In my line of work if I wait to be lead by the nose and try to avoid being the one who is willing to be responsible for being out in front of the curve I would be dead in the water. BTW thanks for avoiding the BUTT DYNO jokes they suck.
4by4,
I have inspect that part closely and it seems to restrict flow quite a bit when the flap is open.
I am also thinking of removing the flap and possibly remove/grind off the the divider that spit the air intake. Grinding off the divider will take lots of time.
I believe once the valve is removed there is no way to put it back on.
if some of you guys saw I removed those to paint the intake manifolds, I saw the way they are held in. There is a ring holding a metal bar. If you remove it there will be 2 holes where it was. (can easily be plugged -yes) Low end torque loss is a yes. The throttlebody being closer alone is a big improvement. I mentioned this when the RSS/IPD was introduced a few months ago. I am actually getting one soon hopefully. $995 for 20HP is a good deal.
I all likeliness I will get the Plenum as well, however this mod may be ok for some people.
Now...just need to verify it improves the power up top.
IF I get the RSS/IPD plennun, and later decide to go after a turbo kit say form TPC, will this plennun still work?
Just out of curriosity, any posters on this thread happen know what particular components, if any, might have been used by Porsche to create a "....
...
resonance induction system with a
variable-length intake
manifold.
..."
for the Cayman?
Or is the variable-length intake manifold just another feature the 911 3.8 liter motor's got, that the Cayman was denied? Brilliant! ~
Cheers
The
Cayman
has this system. Its the whole assembly as seen in the pic on the first post. The flaps are used to tune the resonance. Go to the Plenum thread to read more about it. I also posted a link on the way the resonance induction works. Actually its very simple and clever, the current system is certainly not perfect, but then again given the space in the engine bay its a good result.
Tuning the intake
The intake system on a four-stroke car engine has one main goal, to get as much air-fuel mixture into the cylinder as possible. One way to help the intake is by tuning the lengths of the pipes.
When the intake valve is open on the engine, air is being sucked into the engine, so the air in the intake runner is moving rapidly toward the cylinder. When the intake valve closes suddenly, this air slams to a stop and stacks up on itself, forming an area of high pressure. This high-pressure wave makes its way up the intake runner away from the cylinder. When it reaches the end of the intake runner, where the runner connects to the intake manifold, the pressure wave bounces back down the intake runner.
If the intake runner is just the right length, that pressure wave will arrive back at the intake valve just as it opens for the next cycle. This extra pressure helps cram more air-fuel mix into the cylinder -- effectively acting like a turbocharger.
The problem with this technique is that it only provides a benefit in a fairly narrow speed range. The pressure wave travels at the speed of sound (which depends on the density of the air) down the intake runner. The speed will vary a little bit depending on the temperature of the air and the speed it is moving, but a good guess for the speed of sound would be 1,300 feet per second (fps). Let's try to get an idea how long the intake runner would have to be to take advantage of this effect.
Let's say an engine is running at 5,000 rpm. The intake valve opens once every two revolutions (720 degrees), but let's say they stay open for 250 degrees. That means that there are 470 degrees between when the intake valve closes and when it opens again. At 5,000 rpm it will take the engine 0.012 seconds to turn one revolution, and 470 degrees is about 1.31 revolutions, so it takes 0.0156 seconds between when the valve closes and when it opens again. At 1,300 fps multiplied by 0.0156 seconds, the pressure wave would travel about 20 feet. But, since must go up the intake runner and then come back, the intake runner would only have to be half this length or about 10 feet.
Two things become apparent after doing this calculation:
1. The tuning of the intake runner will only have an effect in a fairly narrow RPM range. If we redo the calculation at 3,000 rpm, the length calculated would be completely different.
Ten feet is too long. You can't fit pipes that long under the hood of a car very easily.
2. There is not too much that can be done about the first problem. A tuned intake has its main benefit in a very narrow speed range. But there is a way to shorten the intake runners and still get some benefit from the pressure wave. If we shorten the intake runner length by a factor of four, making it 2.5 feet, the pressure wave will travel up and down the pipe four times before the intake valve opens again. But it still arrives at the valve at the right time.
There are a lot of intricacies and tricks to intake systems. For instance, it is beneficial to have the intake air moving as fast as possible into the cylinders. This increases the turbulence and mixes the fuel with the air better. One way to increase the air velocity is to use a smaller diameter intake runner. Since roughly the same volume of air enters the cylinder each cycle, if you pump that air through a smaller diameter pipe it will have to go faster.
The downside to using smaller diameter intake runners is that at high engine speeds when lots of air is going through the pipes, the restriction from the smaller diameter may inhibit airflow. So for the large airflows at higher speeds it is better to have large diameter pipes. Some carmakers attempt to get the best of both worlds by using dual intake runners for each cylinder -- one with a small diameter and one with a large diameter. They use a butterfly valve to close off the large diameter runner at lower engine speeds where the narrow runner can help performance. Then the valve opens up at higher engine speeds to reduce the intake restriction, increasing the top end power output.
The intake manifold in the Cayman is adaptive. It allows the air oscillation in the intake to be adapted to the respective engine/air speed. This aids the engine in making more torque at lower speeds without losing power at higher speeds. There are two flaps in the intake, a distribution flap and a resonance flap. The Distribution Flap opens from 3,500-4,900 rpm, and again from 5,200-7,300 rpm. The Resonance Flap opens from 4,700-7,300 rpm.
