Hot Air Intakes

I was just bouncing around on the board the past few days, unrelated searches. I've come across posts that interest me about Air Intakes and the whole debate about "Snorkel" and whether the intake in the engine bay, without a dedicated snorkel, is a Hot Air intake... so I'm fishing here. I've been a member on the board here for 16 years with hardly a post, so no flames necessary, please... Here's my question - directed to all the nay sayers about CAIs. How do you know, and do you have any empirical evidence to support the temperature differentials between the stock airbox (or the 3.8 airbox mod) and the aftermarket CAI solutions, like the Fabspeed dual cone intake (I have)? If so, please share... and I'll go ahead and share my empirical and anecdotal evidence. I have an '02 3.6, I put the Fabspeed dual cone intake and the fabspeed cans on, nothing else, engine-wise. Here are "my facts": The look and the sound is awesome to me - just enough to sound a bit better, and the intake sound at WOT and 5k+ rpms is just fun... so power aside, I quite like the bolt-on based purely on sound & aesthetics. I ran an OBD port monitor today and drove some mixed city/hwy driving heading to a doc appt. Ambient temperature on my dashboard showed 78 degrees. Temperatures "reported" via OBD to the air intake were generally about 8 degress higher on the highway. Temps went up pretty quickly in stop and go traffic w/stop lights to 20-35 degrees higher... no question that's not awesome. But I'm not generally too concerned about my engine's power output in heavy traffic, am I? Those temps dropped back to about 8 degrees above ambient within about a mile on the highway. (I'm sure that the spoiler being elevated didn't hurt. Also, keep in mind, I didn't modify the rear deck lid by cutting out a window on the non-ported side - all stock. (screen shot below was after I parked in a lot) ** UPDATE , Day 2 testing: I calibrated temps when I was inside my garage at cold start and after adjusting for the differential, the air temp reported at the intake on the highway would be more like 2 degrees higher... perhaps the heat shield actually works to keep the air coming into the filters cooler Lastly, I have a good friend, fellow autcrosser, with a 2004 with a before/after Dyno result that showed about about a 25HP gain with the CAI alone... this was done by an independent shop in SC. I know that's crazy, but that's also about what Fabspeed claims on the website... I'm not gonna try to stand on this, but it is a valid data point that i trust from someone I know personally. So look - again, no flames necessary, this is a friendly discussion thread - why all the haters on "hot air intakes" if the WORST case is an 8 degree increase, which I would guess is probably not much different than what you'd see with a snorkel intake, once heat from the intake hardware (whatever you have) seeps into the equation? How much power do you think 8 degrees will rob from your engine? While an 8 degree increase isn't a "cold-air" solution, it doesn't seem to me to be worth disparaging quite as much as I seem to witness on previous posts.

OP - Simple temp/vol math is a 4% power loss for a 25 deg f increase. Heat kills power. Dyno results are always subject to the old saying, �Figures lie and liars figure�. Some intakes work well, some work sometimes and some never work with respect to power. I never liked the way the CAI term has been marketed and hyped. For me, it�s not a cold air intake if the air at the intake isn�t colder than ambient. My opinion for folks is do what trips your trigger. Many of these intakes are art. Many enhance the sound experience. We all have different goals for our cars and their performance. You know why no one posts a forensic deep dive into cold air intakes? A study that takes a stock 3.6 engine for enough dyno runs to account for different conditions, air filters and intakes; then takes a modified 3.6 with larger throttle body, tune, optimized exhaust flow and head work to demonstrate what max performance gain (under like conditions) results, is a daunting and expensive endeavor.

As long as you like the sound thats all that matters. My gripe against cold air intakes that remain in the engine bay is that the name is misleading. If you want to call it a cold air intake, route it outside the grill, or in front of the radiator stack at least. I have no data to share, I just dislike false advertising, I was calling these hot air intakes long before I was a part of any forum or online car discussions. I'm assuming(with all that entails) any increase in power you'd see from a hot air intake is from the aftermarket air filter itself, whether it be larger surface area, less restrictive, or both. I truly have no problem with the products themselves, depending on the application they certainly can provide performance benefits, but I will always mock the name since its an outright lie

Replies and sentiments very much appreciated. My first experience was doing a DIY Dinan CAI with an old, beloved 2001 BMW 7401 Sport (e38). That required some dremmeling through one of the shrouds to get the cone filter behind the front bumper - out of the engine bay completely. They claimed +15 HP at the flywheel, but I didn't care about that much, either - because the sound of that thing howling at WOT was so much nicer than stock. And that's another nice feature about a "modified intake" - it sounds great when you want it to sound great, when you're flogging the car. Doesn't matter what intake you use, I don't see how a "Cold Air Intake" will ever match some people's definition uunless you're ACTIVELY cooling the intake air below ambient air temps before it hits the throttle body. Not sure that's something anyone's done... so since there's no "Cold Air Intake" that I'm aware of, I suppose you can now just say there are two types of intakes: Intakes that attempt to get air at ambient temperature (and accomplish that within a few degrees). We'll call those... ummm... intakes ? or intakes that suck in the hotter air in the engine compartment with no attempt at isolating the air source away from the hot engine bay... We'll call those hot air intakes ? So - there's my thoughts - and in my reasonable opinion (no need to cite engineering credentials, etc), the Fabspeed Comp Intake, by way of the heat shield and the open air port on the rear grill do indeed isolate the intake air to achieve temperatures very close to ambient air temperature when the car is in motion above, say 60mph, or even better, above 72mph when the rear deck lid is raised. Whether the HP claims are true, we can leave that to the other debates. And when operating below those speeds, then it's clearly a hot air intake as stipulated by the naysayers - again, not really a situation where I'm as concerned about maximizing my engine performance - In short, I choose to eat the potential loss (max 4%) because I'm not a "boy racer" trying to outrun traffic between stoplights. Thanks for humoring me...

Out of curiosity, any problems in heavy rain and touchless car washes?

I would be less concerned with air temp and more concerned with how a non factory intake affects the ability of the ECU to fuel appropriately due to the revised plumbing changing the conditions the MAF sees. It was not uncommon in a previous life in a previous application to see the change of intake cause AFR to go to dangerously lean levels. Given the factory calibration on the M96 being so lean to start with, if it were me I would be wanting to see what a wideband 02 sensor says for any pre-TB modification where the MAF is retained..

Quotes source post: 19709522

Never a problem in heavy rain - I've sprayed the deck lid at a high-pressure self car wash while the engine was running and heard the idle glitch a bit but just a brief sputter.

Quotes source post: 19709531

Fair point - I suppose this could be an issue, and I never opted or even considered tuning the ECU. I would expect that the stock ECU could monitor, and hopefully adjust appropriately, for the change in air volume.... but I don't know that for a fact. I do know I've had the setup installed for over 10 years / 20k miles and I've done a few track days and I've never had a code thrown, nor anything to indicate that the engine is running too lean.

You Tube

The ECU can correct fueling to an extent, that is as long as it knows how much air is going into the engine. That information is provided to the ECU, in part by the MAF sensor. So, if the MAF is feeding the ECU bad info because it’s placement or the airflow it sees does not mimic what it sees in factory trim - it corrects based on inaccurate information.

Quotes source post: 19709583

Compelling video, but seems like apples and potatoes comparison for an FSI rebuilt / remapped engine. What do I know? Already saw this elsewhere and again, probably not worth debating power. As I said, I have a similar example with apples to apples, M96 3.6 stock engine with the same comparison that shows otherwise.

Quotes source post: 19709591

So, yeah, I'm an engineer, and an old one... I'm not a EE, I'm an ME/IE - but concepts are concepts... and if I get something wrong, be kind. Okay, I'll bite... and try to geek out... The MAF works to measure what it thinks is the air mass flowing past the sensor's wire and cooling it to a preset temperature - modifying the current as needed to achieve/maintain that static wire temperature as the airflow / air mass changes dynamically. The stock airbox has a round tube that the sensor is mounted to / inserted into the tube. The aftermarket version has a round tube that is likewise used, and I'll just assume that the depth of the sensor is identical (maybe a tall assumption, dunno). More airflow / air mass and how it's measured whouldn't really be impacted given the similar size / shape of the tube, and the identical placement of the sensor inside that tube, right? I mean, pressure could change - but the MAF isn't measuring pressure, right? It's trying to measure air mass as it "flows" over that platinum wire, I think. And in that case, I can't imagine that (assuming the same shape/cross section/placement) the larger volume of air would suddently present "bad data" to the ECU. Again - not trying to be the smartest guy in the room here - just tossing out my perspective.

I originally popped on the board a few weeks back to look at some oil stuff, recommendations, etc. I've been testing my oil (UOA) and switched from Motul 8100 to Driven DT40 on this change, added the LN Spin-on filter adapter, etc. Now changing oil every 6-8 months even with less than 1k miles on the clock... Just trying to keep things tip-top... contemplating and simultaneously dreading the damn HVAC vent repair.. and.. This is why I don't lurk too much on the boards here! Man it can really suck a lot of time... found this thread in the 997 forum from 2016. https://rennlist.com/forums/997-foru...surements.html

The MAF samples a very small amount of the intake air flow. The ECU multiplies that by the known cross sectional area of the intake around the MAF and any turns/obstructions in the vicinity of the MAF. The size/shape of the intake 2" either side of the MAF is critical to the ECU calculations.

That video is not on a moving car there is a ram air effect from the snorkel I’ve had mine on for a few years and will never take it off love the sound and I do feel a bit more power plus when I open engine lid I get HARD LOLOL

Quotes source post: 19709954

Sorry... but I don't follow your post... it "samples" what? It's literally monitoring the cooling ability of the air flowing over the wire.. the wire being heated by an electrical current. And the air's ability to counteract the heating... more air, lower temps, more cooling effect. I'm sure that cross section should be roughly equivalent and any turbulence in the air flowing past it would be an issue, but you kinda have to expect these are similar diameter tubes without any substantial differences in the mounting of the MAF inside the tube, right???

Quotes source post: 19710046

The MAF has a little window for air entry, so the word �sampling� is used appropriately. However, you�re spot on about the MAF�s function, too. Regarding the cross section of the pipe; you have to hope that the manufacturer produces a pipe with the same diameter. The cross-sectional area of a circle is the squared product of its radius, so a small change in diameter will lead to inaccurate MAF readings.

I try not to use phrases like " you kinda have to expect" or "I'll just assume". There are tons of examples of intakes causing fueling variance from stock, if the OP decides that is not the case for the 996 for whatever reason, that's fine. Leaning out an already lean fuel strategy could be detrimental though and was the reason why even if an intake could pick up 5HP or more, when I still had an M96, I would not put one on my car without recalibrating the ECU.

[QUOTE=eDoug;19709662 More airflow / air mass and how it's measured whouldn't really be impacted given the similar size / shape of the tube, and the identical placement of the sensor inside that tube, right? I mean, pressure could change - but the MAF isn't measuring pressure, right? It's trying to measure air mass as it "flows" over that platinum wire, I think. And in that case, I can't imagine that (assuming the same shape/cross section/placement) the larger volume of air would suddently present "bad data" to the ECU.. [/QUOTE] As the ID of the tube changes, even minute changes, so does the pressure. Increase ID(all other conditions the same), pressure and velocity go down, lower pressure means less dense fluid. If the DME doesn't know the ID has changed it cannot correctly adjust fuel. You are correct that the MAF is not measuring pressure but it is measuring mass flow under what it believes are the same exact conditions, it doesn't know the ID of the intake tube/location in the intake tube has changed.

I used the word "sample" intentionally. The window in the MAF is about 0.1 square inches, so the ECU multiplies the mass air flow in that tiny window by the "known" area of the intake tube. So if the area of the intake tube changes the ECU multiplies by the wrong number. As stated the area of a circle varies with the square of the diameter so small changes in diameter result in large changes in area. Back in ancient history systems like CIS-E or L-Jetronic did use a "MAF" that measured all the air, but those MAFs are a big restriction to air flow.

Quotes source post: 19711765

Not trying to be argumentative - but I don�t see it that way. The �window� is not a window, it�s a piece of wire. The length of that wire is a factor only in that the level of electricity required to heat it up is driven by its resistance. The airflow �cools� that wire - and I think that the intention of that design is that the wire allows free flow of air over its surface, regardless of length as long as the apparatus holding that wire doesn�t disrupt airflow. But again� hey, if you know more than me, I�m okay living in my own fantasy world. Sample is a fair term - but perhaps misleading. I agree that the cross section will impact air velocity which would impact the cooling effect, as would ambient air temp.

@eDoug I applaud you in your knowledge of exactly how a Hot Wire MAF works and you are exactly correct in the small picture, but in the big picture as has been stated the MAF Sensor is Calibrated to the MAF Housing and Produces a Digital Data Air-flow Map that the DME uses to calculate AFR.... It is a 3 component process to get the digital data to the DME for use to get the correct AFR...(1) the SENSOR (2) the Housing (3) the data MAP .... They are all 3 used to get the digital data for the DME, and if one is changed another has to be changed .....IE, if the Housing size is changed the data MAP has to be changed also.....If the sensor characteristics are changed the data MAP has to be changed ect... In other words you can use a completely different Sensor and Housing size, but you will need be to make a compatible digital Data MAP to correct the voltage signal to Liters/grams per minute/second of air flow... In a few words on the History on "Cold Air INtakes"...that started back in the 1960's when normal cars actually had ducts to the exhaust manifolds to get hot air to the carbs. the hot air was better for fuel atomization and emissions......The performance cars had "Cowl Induction Hoods" or "Shaker hood Scoops" and some like the Ford Thunderbolt even had ducts ran to the outboard headlights on each side ( they had 4 headlights but the two outer were used for "Cold Air Intake"..) .. And you know how Hot Rodders are,, they love "nick-names" like "Pink Rods" and "30-30 Cams" for the Bow-Tie Boys... so all Hot Rodders were designing ways to improve air intake on passenger cars.....K&N has always been big into low restriction air filters, and restricted air filters were a common thing back in the day... So many a person was using bigger/less restrictive air filters and duct work,,,,.. There was even a "Performance Spray" that you could spray on the cotton gauze K&N filter to boost the power.... It was a mixture of Polyethylene and Nitro-methane as an oxygenator to boost power if you jetted a bit rich on the top end... So yea, "Cold Air Intakes " have a lot of History but is used out of context so often nowadays it is not worth arguing over, but the History is interesting...

Quotes source post: 19711783

The window is the opening at the bottom of the sensor, next to the rounded corner. 996 MAF sensor