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We did some back to back testing with stock airboxes and then with our front mount intakes to see the actual gains on our shop M3. Same day, same conditions, same car.
Hood closed. 3 runs each, tested with engine and components at operating temperature with brief cooldown between runs. DCT trans, 5th gear. Runs 0-2 are stock airboxes/filters/ducting. Runs 4-6 are Maximum PSI intakes without socks
2016 F80 M3
JB4 on Map 2 – 93 octane fuel
Maximum PSI catless downpipes
We were expecting 10-15whp at best at this power level, and possibly larger gains on E85, meth, etc. Upon reviewing the results we immediately noticed a trend. If you compare runs 0-2 vs 4-6 you can see significant gains above 5700rpm even with a JB4 and downpipes. The gains will likely be better with higher power output cars(upgraded turbos, full exhaust, race fuel/e85, etc.). We normally post all of our results with SAE correction, however the N54/N55/S55 community seems to use STD or uncorrected, smoothing 5.
Here is a graph of the best run from the stock airboxes(blue) vs the best run from the Maximum PSI intakes(red). You can see a notable gain in the upper rpm of over 30whp:
Why did our intakes make more power than stock (and other aftermarket ones)? This is where I get to speculate a bit:
- The oem system (and several aftermarket systems) use the factory ducting that basically draws air from the same place. The oem system is completely sealed, and has a charcoal filter plus a paper one(restriction#1). It then draws ALL of the air through the kidney ducts (restriction #2).
- Aftermarket intakes that use the lower halves of the oem airbox and oem ducting have larger filter elements, however they are now drawing a blend of hot air from the engine bay and the air coming through the ducts. That results in an unrestricted pipe, however AIT’s are higher, resulting in hotter charge air temps. The intercooler is only as efficient as the air entering the system.
- If you decide to try a drop-in filter like BMC or K&N you may eliminate some of the restriction, however it is still using a torturous path with rectangular passages and various less-than-smooth transitions. Our system is 3″mandrel bent piping throughout.
We wanted to address a few customers questions and concerns:
We plan on making significant power with this platform, and took that into account when designing the intakes. We chose the filter size and location for performance and aesthetics. The filters are large, however BMW did an excellent job of ducting all airflow through the kidneys and into the heat exchanger and radiator, regardless of what is in front of the ducts. If it is needed, a slightly smaller filter length can be used. Until that point, this is the route that we prefer. There is plenty of airflow to go above and below the filters and into the ther cooling components. The filters simply get first prority.
We have obviously took into account driving these cars in the rain with exposed filter elements. I have done extended driving through heavy rainfall with no issues. The ratio of airflow going through the filters vs the amount of rain that will contact and be ingested through the filters is not enough to have any concern. People pay good money for water injection to allow for charge air cooling. Look at the M4 GTS that comes with water injection from the factory! I’m not saying we are intentionally trying to have water enter the system, only to say the small amount contacting the filter elements will dissipate long before there is any concern for water ingestion. Someone equated driving in the rain similar to spraying a power washer at the air filters. That is certainly NOT the case. A power washer directed at the filters.
Regarding hot air being drawn from the radiator to the filter, the only situation that would exist is sitting at idle, where it does not matter. As soon as there is forward motion the car gets forced air into the kidneys. The airflow will be past the filters, and through the radiator. There will not be enough time to have any heat radiating forward towards the filters. We easily confirmed this on the dyno with relatively poor airflow.