well, i too personally feel the high rpm gains associated with modifying the intake for higher flow outweigh the low rpm losses that result from any de-tuning that occurs, which is why i am currently running a 997 plenum, cayman throttle body and 85mm BMC DIA airbox.
i have located my maf closer to the throttle body (like in a 996) as well. unfortunately, this has resulted in the need for a bend in the ducting immediately before the maf. i think i will have to rework my intake geometry in general (remove the engine compartment insulation so that i have room to mount my airbox a little lower and get things straight); fact is, the oem intake geometry is pretty good as-is. turbulance and maf reading? unsure. oem porsche airboxes do put a screen before the maf, but it is not a full honeycomb as is available aftermarket. i am currently re-using the maf housing from my old airbox so had to cut-off the screen, but am thinking i need to add something as i'm getting a bumpity idle. otherwise, i am currently using flex duct for my intake tubing. aftermarket vendors get all up in arms about flex duct and try to sell you $300 work of pre-formed plastic pipe under the auspices that flow is less turbulent, but i'm always brought back to the stories of the russian mig fighters and the fall of communism. here was a plane that was relatively on par with anything the west could produce, but when we finally got a chance to look at one we found that it was ill-made and replete with exposed rivets, bumps, lumps etc. all this served to create a layer of turbulent airflow which was much more frictionless than anything you could design. similarly, flex tubing should create a small layer of turbulence that will enhance laminar flow within. |
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I am speaking about airflow losses here not hp. |
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You would have to run the numbers and test to know whether the flex duct is giving significant losses but generally you can expect pipe friction losses I can concur with the feeling that bottom end is slipping away for a more explosive top end above 4k as more intake opening changes are made. It's worth it for making passes on the track but not so much for pulling out of an underground parking garage with a cold engine |
Regarding the honeycomb/screen in front of the MAF, this should be there! Don't ask technical details but let's say it evens out flow and makes for better reading. A lot of knowledgeable people say so.
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Even the after market makers add the screen in front of the MAF
http://www.vividracing.com/catalog/w...10-intakea.jpg Agency Power Cold Air Intake Porsche Boxster 986 98-04 |
Lots of good info
Radium King, Thanks for breaking all the math down. It all makes more sense, as far as calculating airflow, etc.
Homeboy, it sounds like you're selling something. Not a bad thing, if you are. Let's see it! I have used CAI's on my other cars, including Mustang, RX-7 and RX-8, with varying degrees of success. Honestly, one of the reasons was that is was an easy way to add something interesting to look at under the hood. This isn't the case with the 986, since nobody is going to see it, and it already is somewhat a CAI. Referring to high-end gain at the expense of low-end, I would have been interested while I was in Germany, driving the autobahn. In the states, I have to agree with the poster who said he has enough power to put him in jail any day. Still interested, if there is something out there. The vivid racing product looks like it has potential. |
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I was hoping to get posters THAT HAD CAIs to come forward and SHOW THEIR INTAKES. There are several members who have "done it themselves" (@Sparker, @Insite, @CarbonFiberNut, etc.). I know, I PM'd them about their designs. And there are really good ideas out there. The solution is usually an amalgamation of designs. That is what I am trying to accomplish…if I can help the next guy, great! I DID design a Wind Deflector that WILL NOT FALL OUT, cannot be stolen, and is good at race speeds….did I sell it? Not one….I have decided to GIVE IT AWAY instead! http://986forum.com/forums/uploads01...1351944931.jpg As I do not have time. I create a lot of things, such as HH2Go - a Hydrogen system for cars, used in CA and other countries. We were able to almost double gas mileage but were shut down by lawyers….since then I have not really tried to sell anything but homes. I am on my third attempt to mold a fiberglass intake surround around my conical filter, for me. If it can help YOU, GREAT! I have ideas all the time, again not the smartest guy in the room, sometimes they work some times not. Here are some that I uncovered…. http://986forum.com/forums/uploads01/CAI21351944570.jpg http://986forum.com/forums/uploads01/CAI11351944451.jpg http://986forum.com/forums/uploads01...1351944489.jpg http://986forum.com/forums/uploads01/CAI11351944542.jpg http://986forum.com/forums/uploads01...1351944607.jpg http://986forum.com/forums/uploads01...1351944637.jpg http://986forum.com/forums/uploads01...1351944668.jpg http://986forum.com/forums/uploads01...1351944691.jpg And this is the Honeycomb Filter ($10) - and no I am NOT associated with the Mfr. http://986forum.com/forums/uploads01...1351944762.jpg Hope that clears it up! |
Homey, I love that carbon fiber set-up. I like the way you and King have explained flow rates. I've been saying the same thing and tried to show the restrictions in the OEM assembly. That's why I've gone to the EVO.
Just like anything else, shortest distance between two points is a straight line (and a whole lot less restrictive). The sound ain't so bad nether. |
mine is similar to insites (second from bottom) but using a larger airbox (his is 70 mm output, mine 85 mm) and some different ducting; i'll get photos up in a bit.
i really like the cayman intake (last one) and think it is the simplest and cheapest to diy; as per my other posts about that approach, however, i am concerned about performance in the wet. i'd love to hear from someone who drove it through torrential rain and reported on the results. the reduced air temps with the kokeln ram air duct boggle my mind. temp reduction can't be due to the ram air effect as you need to be going really fast before the speed of your car is pushing more air in there than the engine can suck (192 liters per sec. assume the ram air duct cross-sectional area is 2 cm x 10 cm = 20 square cms. 1 liter = 1000 cubic cms, so 192 liters/sec = 192,000 cubic cms/sec. divide by 20 square cms and you get a column of air 9,600 cms/sec long = 96 meters/sec = 215 mph before you are ramming any air in). what i *think* might be going on is: - porsche put the intake at a high pressure area on the side of the car. - wheel wells tend to create high pressure areas at the top of the wheel well. - car aerodynamics try to cause a negative pressure (suction) underneath the car to keep it stuck to the road. - hot engine air is getting drawn out of the engine compartment by the suction, into the wheel wells and out the top into the intake. - the koleln unit, given that it is directional, draws air from further forward on the car and, as a result, gets cooler air. if that is what is going on then that is a very valid product. food for thought (too bad they are so goddamn expensive). |
ps, i defer to jaykay on the rough pipe; mech eng trumps eng phys when it comes to fluid dynamics.
also a quick caveat on those agency or evo-style cold air intakes. to actually be 'cold air' intakes, they have to completely seal against the side of the engine compartment and the engine compartment lid. otherwise, the engine can and will draw air from inside the compartment and this air is MUCH hotter than outside air. the poor fit of most of these units is what has given them a bad name in many circles. the other thing to note is that they come with the housing for the mass airflow sensor (maf). this unit sends a reading of unit airflow to the cars computer. the computer then takes this reading and multiplies it by the diameter of the housing within which the maf sits to determine volume of airflow which is essential to calculate how much fuel to inject. if you change the diameter of the maf housing without reporgramming, the computer will be doing bad math. 2.5 and 3.2 liter engines have maf housings with different diameters. if you look at most aftermarket cold air intakes, they use the same maf housing for all engine types (check it out, the same product number for 2.5 and 3.2 engines) so you really affect your computers ability to adapt. |
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Love the math! Thought the ram air was "fishy" but couldn't put my finger on it. 215mph? The suction in the fender well is a good point. My attempt thus far has been (3rd attempt) to design a "box as round as possible that is sealed" for that EXACT reason. The only way you get better cold air is to seal the source. Would like to see what the King is mackin'. Post pics when you can. |
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Living in Portland, I have not had any issues with bad rain getting in the engine, First rain after de snorking, i drove on the high way pulled over and felt my intake, the grill was dry! maybe luck or the aerodynamics had the heavier water droplets moving faster than the lighter air, so at higher speeds the water does not alter its path. Just like driving with the top down while it is raining, if you go 95+ MPH top down you will stay dry! (Mythbusters did this in a boxster) |
O.K. here is what I have done to give you an update.
I have a large filter connected to a 4" silicone tube, does a 45 degree turn and it is reduced to 3.25", hits the screen from the old airbox (gotta remove that) and the Honeycomb filter, then flows into the MAF. From there it makes less than a 45 degree and it is in the Throttle Body. I am flowing a lot more air! The system took a while to adjust to it but seems to be picking it up now after 20 on/off cycles. The MAF is just above the AOS, maybe a little too close. Seems to be a tad warm there too. Ideally, I will try to get the MAF CLOSER to the Throttle Body, where the flow the MAF is reporting will be EXACTLY what the engine gets! Still working on the "sealed Airbox design" to FLOW ONLY COLD AIR. But for now, it seems to be working with warm air, although not ideal….it is getting FASTER! The acceleration seems to be better at lower RPMs. It is real nice rolling just off the clutch. The engine seems like it will REV FREE and EASIER now! Crisper response and putting plenty of power down. So, in conclusion, some of you should check into moving the MAF closer to the TB. It seems to help the system AND a larger tube combined with the Honeycomb is getting some sweet results! Hard to ignore now! Will update when the sealed airbox is done. I am on the fourth model of it now. Starting to come together! FWIW it has been one of the best improvements YET! All for less than a couple hundred….getting harder to ignore now? |
Unless you have a air leak, the MAF will read the same whether it's inches away from the TB or Feet. If you get it too close, it may actually disturb the air flow, leading to inaccurate readings. That's exactly what they did to the inlet side on the HPTuner site, which made the honeycomb "air straightener" necessary.
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It GOES with the FLOW now! |
So, from your description, I take it the orange one is yours. I like it, I think I will try it.
A few questions: Did you form the silicone tubing, or is there somewhere to purchase it at the right size? I don't see where the honeycomb is installed in relation to the MAF. Could you describe that in a little more detail? Thanks! |
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I do not have one pictured….yet! We should be able to get some snaps of what I am running tomorrow. I DO HAVE SILICONE TUBING, it is from siliconeintakes.com. They were pretty reasonable but the stuff is still not cheap. I do not have the molded one, that would be ideal…no airflow turbulence (or not much anyway). As one poster pointed out, from a thread on HP Tuners site, the Honeycomb filter is used to straighten airflow and allows the MAF to function better. My MAF is currently "just around the corner" from my Throttle Body. I have tried it several places and it seems to like it there. The Honeycomb filter ($10-12) is available through saxonpc.com but you need to know the Inner Diameter (I.D.) of the tubing size you are going to use FIRST. So I have a 10" X 6" air filter using a 4" tubing for about 6 inches, turning using a 45 degree, then to a 4" to 3.25" reducer, into a spacer that is where I have placed the Honeycomb (about 4 inches from the MAF), then it is plumbed to a 45 degree that is slightly cut off and into the Throttle Body. I cut the tubing on the 3.25" tubing b/c any longer: it would be too far, any shorter and it would NOT clear the AOS-which is just BELOW the MAF. Not ideal b/c of the heat but still "snappy"! To give you an idea. Look where your AOS is, draw a straight line UP and the inside turn of the tubing clears it by a couple of inches. I still want to move it closer to the TB. I have another adapter to try. Also, I will apply some heat shielding IF the MAF is staying there. Does anyone know IF A RADIANT BARRIER WILL CAUSE A CONFLICT WITH THE MAF signals? But I think I can get it closer….the closer the better! If I can get a 3.5" MAF tubing section (fits our Pcars-not the MAF but the housing) from a BMW 540i to work, without re-programming, that would be ideal with a stock Throttle Body. Some have bored their TBs out, but I am just not sure IF that would impact your gas mileage. Certainly, more air, if the MAF can adapt…would be the direction I want to go in, so I don't shoot my gas mileage in the foot….even tho the foot is always shooting down the mileage! That is a fun issue, take it up with the brain. When I first started using the 4" to 3.25" tubing the computer was idling the car pretty rough. Acceleration was O.K. but not as crisp as now. I took it out and railed around and it seems to be getting better mileage AND definitely a little more "snap" in the thrust department. Also, I will have a BIG COLD AIR TUBE over the air filter sealed into the vent hole in the side of the car. Have turned the corner by finding a design that has VERY FEW EDGES for better airflow….because if you are flowing 192 cubic meters of air a second…you need it as slick as possible! Thanks for fighting the good fight. Will have pics soon! |
Mpg's
Per the OBC, I'm getting around 28mpg highway. What helped the most, you ask?? The under drive pulley and the weight loss. The 75mm TB and swapping out the factory air box seemed to increase power under throttle, but did nothing positive or negative to mpg under regular driving.
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Nice summary of the challenges in improving on the stock intake design Radium. From my rough calculation, a 2.5L 6cyl motor only requires a 2" ID intake to achieve max VE at redline so I don't have heartburn over the stock design. If I jumped to a 3.4L motor and exhaust I would certainly need to re-tune the intake. No well-tuned intake would be complete without a carefully placed helmholtz resonator to cancel the acoustic pressure wave that would otherwise certainly foul your MAF sensor readings. Bigger and smoother are just the tip of the iceberg in a performance-tuned intake design.
A useful resource for getting the math right: Volumetric Efficiency (and the REAL factor: MASS AIRFLOW), by EPI Inc. |
I have often wondered about the helmholtz chamber on the 3.2 intake. It's basically an odd shaped divergent section. It's much different than an accumulator type appendage which is usually seen. Even an F1 exhaust system has this discrete volume arrangement; have a look at the 2.5 L intake chamber.
Perhaps it's just enough to give some positive effect Sound wise I can't speculate as I now have a large 3.25" pipe and cayman TB....I have needed to stay at 3.00" to give any sort of feedback Oh yeah this thing roars when you floor it on cam.....I feel like I am waking the dead! Quote:
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