thanks for the essay on how a MAF sensor works
The original debate was whether there were any additional gains to be had by adding an aftermarket CAI to a vehicle that ALREADY HAD A TUNE using the stock airbox.
Yes, and the dispute turned into "CAI's make a ton of power. My error codes are proof." Welcome to the internet, where thread discussions often don't follow the original topic :/
And you still need a tune to accomodate a new larger MAF tube even if you already had one for the stock airbox.
If you didn't need a primer on how a MAF sensor is used by the ECU, good for you
holy crap, why don't people learn what they are talking about before arguing?
A different than factory MAF will require a tune because it returns different numbers than the factory MAF. A factory MAF installed into a larger tube requires a tune because the *sensor* is seeing a different rate of flow across the sensor than the factory system.
A MAF sensor measures airflow by measuring changes in the resistance of a wire. The wire changes resistance depending on the mass of air that passes over it. More air, less resistance; less air, more resistance. "More air" can mean either cooler, denser air or air travelling at a higher velocity. In a tube of known cross-section, this gives an accurate measurement of the mass of the air flowing down the tube. Since it can't actually measure the mass of all the air in the tube at a time, the system has to make certain assumtions about the tube the sensor is in.
When you install the factory MAF in a larger tube or when using an aftermarket MAF, the engine is still inhaling the same amount of air, but since the intake tube is bigger the air is travelling slower. Less air is flowing past the MAF sensor for a given throttle opening/engine load situation. The engine is actually getting the same amount of air it was getting before, but due to the larger diameter tube, it travels slower down the tube. The MAF sensor is reading low compared to the factory system under the same conditions. Since the engine is getting more air than the sensor would imply, the ECU ends up not giving enough gas, hence a lean condition.
This lean condition is NOT an indication of a CAI "working." It's an indication that you've increased the diameter of the MAF tube, causing the ECU to underestimate the air mass and deliver less gas than desired for efficient combustion.
Knowing that, it's no surprise that people who put the CAI systems to a scientific test see no gains. And it's obvious why a tune is necessary for a CAI that changes the MAF tube diameter. You might see power from the tune itself, but you'd see the same power from a tune on the factory system.
Excellent write up! That's one of the best, if not the best, explanation I've read regarding why a CAI with a larger than stock MAF diameter requires an aftermarket tune.A different than factory MAF will require a tune because it returns different numbers than the factory MAF. A factory MAF installed into a larger tube requires a tune because the *sensor* is seeing a different rate of flow across the sensor than the factory system.
A MAF sensor measures airflow by measuring changes in the resistance of a wire. The wire changes resistance depending on the mass of air that passes over it. More air, less resistance; less air, more resistance. "More air" can mean either cooler, denser air or air travelling at a higher velocity. In a tube of known cross-section, this gives an accurate measurement of the mass of the air flowing down the tube. Since it can't actually measure the mass of all the air in the tube at a time, the system has to make certain assumtions about the tube the sensor is in.
When you install the factory MAF in a larger tube or when using an aftermarket MAF, the engine is still inhaling the same amount of air, but since the intake tube is bigger the air is travelling slower. Less air is flowing past the MAF sensor for a given throttle opening/engine load situation. The engine is actually getting the same amount of air it was getting before, but due to the larger diameter tube, it travels slower down the tube. The MAF sensor is reading low compared to the factory system under the same conditions. Since the engine is getting more air than the sensor would imply, the ECU ends up not giving enough gas, hence a lean condition.
This lean condition is NOT an indication of a CAI "working." It's an indication that you've increased the diameter of the MAF tube, causing the ECU to underestimate the air mass and deliver less gas than desired for efficient combustion.
Knowing that, it's no surprise that people who put the CAI systems to a scientific test see no gains. And it's obvious why a tune is necessary for a CAI that changes the MAF tube diameter. You might see power from the tune itself, but you'd see the same power from a tune on the factory system.
Excellent write up! That's one of the best, if not the best, explanation I've read regarding why a CAI with a larger than stock MAF diameter requires an aftermarket tune.
However, I have a question and a comment on your last paragraph.
(1) Does the "CAI system" in your 1st statement refer to a "tune required"(larger than stock MAF diameter) CAI installed with an aftermarket tune, a "tune required" CAI installed with the stock tune, or a "tuneless"(same as stock MAF diameter) CAI installed with a stock tune?
(2) I may be misinterpreting your last statement, but it appears that your implying that a tune and a CAI with a larger than stock MAF diameter produces the same amount of power as a tune and the stock air intake. If that is what you're saying, then I disagree. The former produces more power than the latter. This fact has been proven numerous times in dyno graphs posted on various forums, and also in the "Cold Score" article in Mustang 5.0
You're welcome.Thanks!
My point was mostly that unless the stock intake piping is a real choke on the system, you wouldn't see much for gains. I don't know how much of a choke the factory system is.
So, 1) I was thinking of a CAI and tune. 2) It's probably not fair to say a CAI nets zero gain. Just not the 25 hp gains a magazine article would claim. A tune nets power with the stock system, down to the paper filter. Anyone who gets an aftermarket CAI and tune should see benefits over the factory tune and filter.
Are those benefits related to the piping, the filter, or the tune being more aggressive for higher octane gas? A combination of factors? It's kind of tough to eliminate all the variables so we could say for sure. But it might be reasonable to suggest that real world testing by people without a horse in the race would indicate a CAI doesn't show much benefit at the track, comparing tuned stock to tuned modded. But other mods could very well change the equation. The more power you are making the more gains you see from little changes, changes that would be invisible to an otherwise stock system.
The "Cold Score" article in Mustang 5.0 makes the case for aftermarket CAI's. But one test system, from MMR, replaced just the filter and MAF and saw a 12 hp bump with a tune. Swap in their tube, and get another 3 hp after tuning. It's pretty clearly not the intake tube making all the power there.
The Mac system did pretty much the same thing, replacing only the filter and MAF tube on the end of the factory tubing. 14.4 hp gain according to the article if you compare tuned stock to re-tuned with CAI.
The K&N intake pipe showed 11 hp gains comparing tuned to tuned, but appeared to put the factory MAF into a tube the same diameter as stock.
Among all tested systems, they showed anywhere from 8-18 hp gains comparing tuned stock to tuned with CAI. There seemed little benefit to a whole new intake pipe vs. a factory pipe with a new air filter and MAF tube. Kind of proves the CAI tubing is mostly cosmetic and not really beneficial. But the easiest way to mount a cone filter is to buy a CAI
Wow! this info may just save me from spending $600-$700 bucks! I jst assumed a cai was about the first mod you should do b/c of the relatively low cost and gain in hp.
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