PRL HVI MAF Housings Explained
Airflow is without a doubt the most important input for a Type R's ECU. Everything from ignition advance to fueling, cam angles to knock retard, depends on a calculation known as air charge. We won't get deeply into air charge in this article (read more here), but it essentially represents the mass (not pressure) of air inside the cylinders and is derived from the MAF sensor, MAP sensor, BP sensor, and RPM. Without accurate metering from all three sensors, your Type R cannot properly calculate air charge and thus will not precisely control your engine. The majority of people have not reached the limits of the MAP or BP sensor, but the MAF sensor is nearly maxed out from factory.
This presents a big problem for those trying to push even more air through their engine with upgraded turbochargers in order to break the 400whp barrier. Luckily, there are now multiple solutions for those that have the PRL Motorsports High Volume Intake system.
What's a MAF sensor?
The MAF sensor, short for mass air flow sensor, sits inside of the MAF housing and is responsible for measuring the temperature and mass of air flowing through your intake before the turbocharger. It achieves this with two resistors that are constantly heated up. As air flows over them, they cool down and the change in resistance is measured and converted into a voltage that is sent to the ECU. This voltage is then compared to the AFM flow table in your ECU and converted into grams per minute of air.
The issue arises in the fact that the MAF sensor has a limit of 5 volts. Once enough air is flowing over the resistor, it will reach 5 volts and 'go blind', being unable to report any additional airflow. Without disabling the CEL, your Type R will go into limp mode. Even a stock Type R will reach 4.7-4.8 volts by redline, and with nothing but a tune you can potentially be hitting 5 volts, albeit that being rare. With an upgraded turbocharger, it’s guaranteed you will max it out unless you severely limit the power output. This isn't something that can be bypassed via tuning as it is a physical limitation of the sensor. At this point, you have three potential options:
- Disable the P0101/P0103 CEL and cross your fingers that nothing goes wrong
- Replace the MAF sensor with a higher capacity model
- Increase the cross-sectional diameter of the housing the MAF sensor sits in
At this time there is no upgraded MAF sensor that can easily be used with the Type R. However, companies that recently released drop-in turbochargers also realized the need for a larger MAF housing. There are now multiple MAF housing upgrades exclusively for the PRL Motorsports High Volume Intake, undoubtedly the most popular aftermarket intake for the 2017+ Civic Type R.
Front to back: PRL Race MAF, Rampage Fabrications 3.5" MAF, original PRL MAF housings.
How does a larger MAF housing help?
Only a tiny slice of the air flowing through your intake actually goes through the opening in your MAF sensor. By increasing the inner diameter of the MAF housing, an even smaller amount goes through the MAF sensor and thus allows it to measure a larger overall amount of air passing through the intake. The amount the sensor can read increases as a square of the diameter increase, so even a minor increase can actually be huge. Once installed, your tuner simply rescales the AFM flow table and your ECU is now able to properly calculate its targets with higher airflow.
Do I need this?
If you're going to upgrade the turbocharger, you've had a P0101/P0103 check engine light, or the AFM.v sensor in your datalogs is reaching 4.96v, absolutely. The reliability of the Civic Type R depends on these calculations being correct. While your engine will still 'work' when the MAF sensor maxes out, it is a guesstimate by the ECU and could result in significantly unsafe conditions.
Otherwise, likely not. This upgrade will not give you more power on its own. There is a good chance that a larger MAF housing could avoid what we call the 'sine wave' bug by not passing 4.7v, but we will do some testing before making any conclusions here and ultimately that bug is solved by proper MAF tuning anyways.
Importantly, it requires a tune that takes the larger MAF housing into account and cannot be used otherwise without causing major problems. This means you will not be able to return to a stock tune without first swapping out the MAF housing. It also requires a PRL High Volume Intake system and is NOT compatible with any other intake on the market.
Which solution you should choose depends on your needs. Having an overly large MAF housing provides little benefit.
Original PRL HVI MAF Housing
Included with PRL High Volume Intake system
Same specs as factory MAF. Recommended for any tuned Type R with a stock turbo.
Rampage Fabrications 3.5" MAF Housing
PRL Motorsports Race MAF Housing
Notably, the new Race MAF from PRL is so large that it requires an upgraded silicone intake tract as well, with an option for both the PRL Titanium Inlet Pipe and any inlet pipes that are the same size as stock (i.e. the Rampage Titanium Inlet Pipe). This MAF housing is the big daddy and you will be hard pressed to max this out without an equally ridiculously large turbocharger.
The FK8 Clinic has all of these upgrades on hand and we will be testing them back to back on our brand new 2021 Type R equipped with a PRL P600 turbocharger (and many other goodies!) to see how much of a difference they each actually make, and posting the results publicly on our website and Instagram. Follow us at @fk8clinic to stay up to date and watch our build progress!