Who's In The Cold Air Intake Club and What Do Ya Got?

[Kenny Boxster]

The claim that snorkeling is counterproductive is somewhat controversial...

Finally: Dyno charts of de-snorked 986S!!!

I can't find the link to the thread at the moment, but Jake even touts the desnorkling of a 2.5l boxster spec car.

Take caution before it's know-all end all.

~~~ It's also true that our car stock has a cold air intake- albeit a rather inefficient one. I did not believe it was that bad until I actually saw the maze with my own eyes. Don't except a massive jump rocket in horsepower, but you would indubitably free some horsepower up.

[tommy986]

Homeboy,
Do you have any pictures to post ?
List of parts and where sourced?

[Kenny Boxster]

Interesting link. This may also be interesting to those that have modified their intake to be less restricting.

[ProjectM96]

Anyways, I bought the AFE Cold Air Intake. It replaces the stock filter with a performance reusable filter. It replaces the stock intake hose and gets rid of the silencer. It is about the same size as the stock intake hose. Maybe a couple millimeters larger in diameter than stock.

I noticed a slightly louder idle sound and a louder engine sound at 4000+rpm. But as expected, I did not feel any difference in speed. These Aftermarket intakes barely make any difference.

Complimentary mod: clean your throttle body with alcohol or electric parts cleaner while you have the stock intake hose off.

[Homeboy981]

O.K. I feel like the dumbest one in the room now. Anyone for a recess, I was always good at recess.

@Eric G - how does a rocket scientist ever become a road racer? You are way to smart for that! On the presentation, about the second or third slide from the end there was a graph model about larger size intake, and then CFD model showing a larger diameter tubing was called for…interesting that fluid would also serve helpful for mixing gases.

Here is the existing problem with airbox….it shows the piece that is removed is the the receiving end of the snork. It has a 3" x 4" opening….the larger oval part is 8" on bottom, 5" on top and 3.5" in height - that is the intake size the modded air filter uses….


Here is a pic of the "air path" that snakes around inside your Factory airbox…take a look! It is a little hard to see...


Same pic but the arrows highlight with the path the air has to take…


Here is where the filter resides, most of us know this part as we see it when we change the air filter…what you did not know was the "long road" the air is taking to get to your throttle, where it makes the power! Talk about the long way home…


This is where the air is compressed or "flatlined" as I call it. The hole next to the filter where the air flows over the air filer is coming out of is only 2" X 5"!! This SEVERLY RESTRICTS air flowing over the filter…and thusly into the engine.


Anyway, all I know is….I mod practically every car I have ever owned with an air intake. This one is no different, sorry to you die-hard stock fans.

At least now you know what I was referring to when I said airflow is like an "old river" it bends back upon itself….what a waste but it was most-likely done to reduce sound! Just thought YOU SHOULD KNOW

[The Radium King]

ok.

it’s all about moving air.

it’s all about math.

how much air is moving? for a 3.2 liter at 7200 rpm?

four stroke engine, so cylinder fills every second rotation, so moving 3.2 liters / 2 = 1.6 liters per rotation. multiply by 7,200 rotations per minute = 11,520 liters per minute. 192 liters per second. that’s a lot of air.

one could reckon that even small inefficiencies, obstacles, etc., in the intake get magnified when working with such relatively large volumes. fyi, a 1% loss on a 250 hp engine is 2.5 hp.

192 liters per second. that’s called the flow rate, where flow = volume over time. in our case this is also proportional to cross-sectional area of the piping, as air has to flow faster to move through a smaller passage. think about it; you have a pipe that you are drawing air through. flow in = flow out. now constrict the tube in the middle, creating a smaller diameter in a section of the pipe. flow in is still = flow out, but at the constriction the air will have to accelerate to pass the same volume of air in the same amount of time as in the sections of pipe before and after it.

using math, this presents as:

flow = volume / time
volume = area x distance
therefore, flow = area x distance / time
but, velocity = distance / time
so, flow = area x velocity

so, with flow being constant, a smaller area creates a higher velocity.

math.

another thing you would have noticed if you actually did the pipe constriction thing above was that it was harder to draw the air through the constricted pipe. that is because accelerating the air is work, and work requires energy, and this energy is lost as soon as the air slows down (decelerates) on the other side of the constriction. wasted energy. exactly what we are trying to avoid. making the engine do extra work that it doesn’t have to. that is why most aftermarket intakes use larger diameter, equal diameter components.

so why would porsche do this to a performance car?

well, there are benefits to accelerating the air in the intake. if I can accelerate my air so that it is rushing into the cylinder instead of being sucked in then my engine will work less and i might actually get more power from improved cylinder fill on each rotation. in fact, if you open your engine and look at the intake runners that feed each cylinder, you’ll see that they taper slightly as they get closer to the engine. taper = reducing diameter = increasing velocity of air. porsche is working for us.

thing is, that intake valve on your cylinder isn’t always open, and when in closes you have that rushing air slamming into it and bouncing back. this forms a pressure wave that moves back up the intake and can impede airflow. what to do about that? well, if done properly, the lengths of the intake runners can be set such that the air bouncing back arrives just as one of the other valves open, using the bounce-back pressure wave to increase cylinder fill even further. that’s called a tuned intake.

note that you can tune only for a small range of rpm. the tuning is based on the length of the intake runners and the velocity of the air, but as we found above, velocity = distance over time, and changing the rpm changes the time component of the equation and throws the tuning off. all is not lost, however, as porsche has thought about this as well. if you go back to your engine, you’ll see the intake runners heading to each cylinder as discussed previously, but you’ll also see each bank of intake runners joined by two tubes. one of these tubes is called the ‘resonance tube’ and has a vacuum-operated flapper valve in it. the purpose of this resonance assembly is to open the flapper valve at higher rpm, effectively changing the intake runner length and ‘re-tuning’ your intake for higher rpm.

booyakachaka.

a few more points.

since the tuning of the intake is only working 100% for two small rpm ranges, there will still be bounce-back pressure waves occurring and impeding airflow. what you need is some way to get this wave out of the way so that your intake can be as efficient as possible. if you look at your oem intake piping between the throttle and the air box you will see a resonance chamber on it (or even a little appendix-like chamber if you have an earlier car); this is where porsche tries to stall-out the pressure wave to keep the intake as efficient as possible. my theory (ie, not science or fact) is that the great intake sound you hear when you remove this chamber and put on an aftermarket intake is actually the pressure wave interacting with the intake air; you are literally hearing your intake become less efficient.

the plenum (the chambers that join the runners together) should be designed to be at a constant, positive pressure, so that air is always available to feed the runners. the best way to get positive pressure is to have, as before, air accelerating into the plenum. similar to the intake runners, this is achieved by having your intake piping gradually reducing in diameter as it approaches the plenum, and this is where you see the porsche intake on the 3.2 liter engine reducing from 3” at the airbox to 2.66” at the throttle.

the airbox gets treated similar to the plenum, as both serve as air supplies to piping designed to accelerate air. as such, the airbox should be at a constant, positive pressure. again, to get positive pressure in the airbox we have to accelerate air into it. to do this we have a restriction (the snorkel) on the intake.

another consideration is how solids perform in a fluid. basically, accelerating fluids tend to ‘pick-up’ solids, and decelerating fluids tend to drop solids. the mississippi delta is full of mud because all the dirt that got picked-up by the faster flowing river upstream gets dropped when the river slows down to meet the ocean. similarly, decelerating the air in your airbox prior to hitting the filter allows all that dirt/bugs/cigarette butts to settle out before clogging the filter (or setting it on fire).

so, porshe is perfect, right? then why do folks show hp increases with aftermarket intakes, larger throttles, removed snorkels, etc.?

apples to apples. the boxster is a light, underpowered car (relative to the 996) designed to perform in a low speed environment (cities, twisty tracks). as such, porshe tuned the car to extract as much lower rpm torque as possible from the smaller engine. the tuning (resonance chamber, airbox/snorkel, decreasing diameter intake piping, etc.) is designed to maximise performance in the 2,000 to 4,000 rpm range AT THE EXPENSE of high rpm hp. that is, at higher rpm the resonance chamber on the intake piping that was serving to reduce the pressure wave at 3,000 rpm is now just a place where 192 liters per second have to expand and contract (wasted energy) before getting to the engine (remember that, similar to intake runner tuning, the most effective placement of the resonance chamber will vary with rpm, yet it is fixed in place). the smaller throttle body and snorkel designed to accelerate air into the plenum and airbox, respectively, in order to create positive pressure are now just obstacles to airflow as they become too small to efficiently move the volume of air we are trying to move.

if you go back and look at the dynos of aftermarket intakes, throttles, etc, first put on your ‘wishful advertising’ spectacles to try and see through all the vendor murk. next, notice that none of them show any gains, and some show losses, at lower rpms, and the benefits only start to appear at higher rpms.

and this is time I will never get back.

[Homeboy981]

Originally Posted by The Radium King

ok.

it’s all about moving air.

it’s all about math.

how much air is moving? for a 3.2 liter at 7200 rpm?

four stroke engine, so cylinder fills every second rotation, so moving 3.2 liters / 2 = 1.6 liters per rotation. multiply by 7,200 rotations per minute = 11,520 liters per minute. 192 liters per second. that’s a lot of air.

one could reckon that even small inefficiencies, obstacles, etc., in the intake get magnified when working with such relatively large volumes. fyi, a 1% loss on a 250 hp engine is 2.5 hp.

192 liters per second. that’s called the flow rate, where flow = volume over time. in our case this is also proportional to cross-sectional area of the piping, as air has to flow faster to move through a smaller passage. think about it; you have a pipe that you are drawing air through. flow in = flow out. now constrict the tube in the middle, creating a smaller diameter in a section of the pipe. flow in is still = flow out, but at the constriction the air will have to accelerate to pass the same volume of air in the same amount of time as in the sections of pipe before and after it.

using math, this presents as:

flow = volume / time
volume = area x distance
therefore, flow = area x distance / time
but, velocity = distance / time
so, flow = area x velocity

so, with flow being constant, a smaller area creates a higher velocity.

math.

another thing you would have noticed if you actually did the pipe constriction thing above was that it was harder to draw the air through the constricted pipe. that is because accelerating the air is work, and work requires energy, and this energy is lost as soon as the air slows down (decelerates) on the other side of the constriction. wasted energy. exactly what we are trying to avoid. making the engine do extra work that it doesn’t have to. that is why most aftermarket intakes use larger diameter, equal diameter components.

so why would porsche do this to a performance car?

well, there are benefits to accelerating the air in the intake. if I can accelerate my air so that it is rushing into the cylinder instead of being sucked in then my engine will work less and i might actually get more power from improved cylinder fill on each rotation. in fact, if you open your engine and look at the intake runners that feed each cylinder, you’ll see that they taper slightly as they get closer to the engine. taper = reducing diameter = increasing velocity of air. porsche is working for us.

thing is, that intake valve on your cylinder isn’t always open, and when in closes you have that rushing air slamming into it and bouncing back. this forms a pressure wave that moves back up the intake and can impede airflow. what to do about that? well, if done properly, the lengths of the intake runners can be set such that the air bouncing back arrives just as one of the other valves open, using the bounce-back pressure wave to increase cylinder fill even further. that’s called a tuned intake.

note that you can tune only for a small range of rpm. the tuning is based on the length of the intake runners and the velocity of the air, but as we found above, velocity = distance over time, and changing the rpm changes the time component of the equation and throws the tuning off. all is not lost, however, as porsche has thought about this as well. if you go back to your engine, you’ll see the intake runners heading to each cylinder as discussed previously, but you’ll also see each bank of intake runners joined by two tubes. one of these tubes is called the ‘resonance tube’ and has a vacuum-operated flapper valve in it. the purpose of this resonance assembly is to open the flapper valve at higher rpm, effectively changing the intake runner length and ‘re-tuning’ your intake for higher rpm.

booyakachaka.

a few more points.

since the tuning of the intake is only working 100% for two small rpm ranges, there will still be bounce-back pressure waves occurring and impeding airflow. what you need is some way to get this wave out of the way so that your intake can be as efficient as possible. if you look at your oem intake piping between the throttle and the air box you will see a resonance chamber on it (or even a little appendix-like chamber if you have an earlier car); this is where porsche tries to stall-out the pressure wave to keep the intake as efficient as possible. my theory (ie, not science or fact) is that the great intake sound you hear when you remove this chamber and put on an aftermarket intake is actually the pressure wave interacting with the intake air; you are literally hearing your intake become less efficient.

the plenum (the chambers that join the runners together) should be designed to be at a constant, positive pressure, so that air is always available to feed the runners. the best way to get positive pressure is to have, as before, air accelerating into the plenum. similar to the intake runners, this is achieved by having your intake piping gradually reducing in diameter as it approaches the plenum, and this is where you see the porsche intake on the 3.2 liter engine reducing from 3” at the airbox to 2.66” at the throttle.

the airbox gets treated similar to the plenum, as both serve as air supplies to piping designed to accelerate air. as such, the airbox should be at a constant, positive pressure. again, to get positive pressure in the airbox we have to accelerate air into it. to do this we have a restriction (the snorkel) on the intake.

another consideration is how solids perform in a fluid. basically, accelerating fluids tend to ‘pick-up’ solids, and decelerating fluids tend to drop solids. the mississippi delta is full of mud because all the dirt that got picked-up by the faster flowing river upstream gets dropped when the river slows down to meet the ocean. similarly, decelerating the air in your airbox prior to hitting the filter allows all that dirt/bugs/cigarette butts to settle out before clogging the filter (or setting it on fire).

so, porshe is perfect, right? then why do folks show hp increases with aftermarket intakes, larger throttles, removed snorkels, etc.?

apples to apples. the boxster is a light, underpowered car (relative to the 996) designed to perform in a low speed environment (cities, twisty tracks). as such, porshe tuned the car to extract as much lower rpm torque as possible from the smaller engine. the tuning (resonance chamber, airbox/snorkel, decreasing diameter intake piping, etc.) is designed to maximise performance in the 2,000 to 4,000 rpm range AT THE EXPENSE of high rpm hp. that is, at higher rpm the resonance chamber on the intake piping that was serving to reduce the pressure wave at 3,000 rpm is now just a place where 192 liters per second have to expand and contract (wasted energy) before getting to the engine (remember that, similar to intake runner tuning, the most effective placement of the resonance chamber will vary with rpm, yet it is fixed in place). the smaller throttle body and snorkel designed to accelerate air into the plenum and airbox, respectively, in order to create positive pressure are now just obstacles to airflow as they become too small to efficiently move the volume of air we are trying to move.

if you go back and look at the dynos of aftermarket intakes, throttles, etc, first put on your ‘wishful advertising’ spectacles to try and see through all the vendor murk. next, notice that none of them show any gains, and some show losses, at lower rpms, and the benefits only start to appear at higher rpms.

and this is time I will never get back.

@T Rad King, Love the math! And while I agree up to the 192 Liters Per Second, and can concur with most of what you are saying, there is another element that needs to be considered…I will USE the higher RPMs and the needs of my engine are not as great (I can afford SOME lost HP in lower RPMs) to GAIN the TOP HP possible, using more airflow, concepts that you have described to the "T", no pun.

Another aspect that is important is linear airflow, straightening or smoothing the air…air turbulence. There is known work out there that DID NOT exist when Porsche designed this car, so what would be the reason not to use that technology?

What other tuners have discovered, again more recently than when our cars were designed, was that by using a device to "establish a more uniform airflow" the horsepower gains are derived from more fluidity over the MAF, allowing the car to adjust the optimum performance.

Since you know of whence you speak, check out this thread (it for Tuners for V-8s, concept still applies):

100mm Maf kickin my Butt!!! - HP Tuners Bulletin Board

Let us know if the part they are speaking of, in terms you we understand, will be of any benefit. I am unable to test it today, so i would like your opinion. :dance:

[stephen wilson]

Are you trying to say Porsche didn't know you have to have smooth laminar airflow to the MAF for accurate readings? This is NOT new information, and has been know for decades in automotive and industrial flow applications. The only reason honeycomb "air straighteners" had to be used on that site is because they totally screwed up the factory intake flow characteristics.

I'm not saying the factory intake can't be improved for high RPM power, but internal or external airflows are not always as intuitive as you might think. The only way to be sure of your results is by detailed calculation, CFD, and objective testing.

[barkinfool]

TRK -

It is true that you won't get the time back, but when you die, you will achieve total consciousness.

So you have that going for you, which is nice...

Thanks, your post was very helpful!

[The Radium King]

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.

[jaykay]

Originally Posted by The Radium King

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.

I would think flex tubing would constitute a "rough pipe" which will translate to flow losses. An open surface with dimples is a much different animal and has been found to enhance laminar flow (non compressible regime).... like aircraft skins; golf balls..

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

[ccstud17]

Originally Posted by barkinfool

TRK -

It is true that you won't get the time back, but when you die, you will achieve total consciousness.

So you have that going for you, which is nice...

Thanks, your post was very helpful!

YES CADDY SHACK!!!


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)

[Homeboy981]

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?

[Kenny Boxster]

Originally Posted by The Radium King

first put on your ‘wishful advertising’ spectacles to try and see through all the vendor murk. next, notice that none of them show any gains, and some show losses, at lower rpms, and the benefits only start to appear at higher rpms.

and this is time I will never get back.

Indeed you should always be skeptical when taking in manufacturer's claims. That being said, one of my favorite quotes is there are lies, damned lies, and statistics. Your application should be catered to your driving habits, wants, and needs, so some folks want prefer higher end horsepower, and some lower end torque. Interestingly enough there's a graph of a guy who did a CAI and scoop to draw in more air. I don't thing there's any ulterior motive for this guy to fabricate his results, unless of course he was paid by kokeln, which I doubt.
http://www.m96infosource.com/site/2011/04/21/boxster-s-ram-air-intake/

In conclusion, there's merit in a less restrictive airflow, but some folks have different preferences in the power bands and torque ranges.