Installing the RPI scoop and skid plates on the M Coupe

As part of my winter itch, I decided to do some work on my car. It’s not quite as fun as driving, but it does have a certain sense of accomplishment. The M Coupe is a pretty low run vehicle, there are fewer on the roads than say Ferrari 430s by 2-3x. This of course limits the number of people doing real aftermarket R&D on the car. As with swapping any OE with aftermarket parts you really have to do your research separate the crap (stuff companies have designed for another car and just shimmed to fit) versus stuff developed and tested for your car; never trust an aftermarkets dyno numbers, etc.

Enter RPI. A small shop out in Irvine California that does serious R&D on BMW, Porsche, Aston Martin and amusingly Nobles. Frankly I respect any small shop doing real engineering, and RPI definitely does just that.

Armed with a socket wrench, pliers, elongated screw driver and iPad, I installed their skid plates and ram air scoop on Sunday.

Skid plates were something I probably should have acquired long ago. They bolt directly onto the front ‘fangs’ and protect the car’s inferior 4″ of ground clearance from whacking on drive ways. It frankly took me half a year to reliably back out of my parents driveway without whacking the nose at the bottom of their driveway, even very slowly. Thankfully these impacts caused only minor scuffs to the bottom of the fangs. The plates are nicely powder coated black aluminium. Installing the plates was trivial: simply removing the hardware already holding the fangs up, lining the plates up, and screwing it back in. They sit fairly flush and provide an aluminium barrier against potentially worse impacts. This exercise added a modest 186.5 grams to either side of the front nose, not particularly bad.

Before we talk about the scoop, I want to take an aside to talk about induction modification. I had done a full on air box swap on my 325i. It was an AFE unit, cheap but enjoyable. While it did provide major improvements to the mid-range power, it seemed to loss power at low speeds and in hot weather (i.e. traffic). A bit of tinfoil and furnace tape improved things. The unit was definitely generic, sorta cut to fit the 325i’s M54B25. The gains on the box, website, etc were all for an unrelated car. Either way it actually did improve around town performance, fuel economy and produced a howl that was nothing other than frightening.

Onto the M Coupe. Being a purpose built high-performance car, the air box is actually quite good. Never the less the usual group of suspects have trotted out a part that will fit, many (including AFE) appear to *lose* power though. In fact, aside from the Gruppe-M unit (absurdly priced at $1100 for a carbon fiber tube), they all seem to be nothing more than noise makers. Having said that, there seem to be gains to be had from changing out the stock intake stack to a ram air scoop. RPI claims 8HP at 100 km/hr, repeated dyno runs, hood closed (with a fan @ 60mph). As with all performance modifications, gains claimed by the manufacturer should be taken with a grain of salt. Thankfully enough trust-worthy people seem to back these claims up, and 3rd party dyno results have agreed.

The obvious question many people ask is, why would a small aluminum scoop add power that BMW didn’t seem fit to obtain? This looks to be a case of trade-offs vs performance. The stock stack is turned up, only getting the air that rises to the top of nose section of the car (more on this later), while the new scoop faces outward. The big trade off here is filter wear and filter cleaning. The air box filter needs to be cleaned far more often, and replaced more often. To an enthusiast willing to do work on his own car, this isn’t really so much of a problem.

Removing the stock cup was pretty trivial, a few clips to be removed (one of which needed the pliers), then the unit was slid out. Thankfully, unlike the e46 3-series, the e86 M coupe has a lot of hood. This means that the engine is further back in the chassis, and also there is a lot more room to move your hands around. The biggest difference, even between the e86 (Z4) and e36 (Z3) M is the nose section. The nose on the e86 is ‘lengthy’ and completely separated from the engine bay. It contains the extra oil cooling and chassis bracing the M demands. Also it gives a good few extra inches that can be used for the ram air scoop. Installing the scoop required positioning it to feed the air box, and then screwing in 3 self tapping screws. Lining the scoop up took a bit of fiddling, but in the end it fit perfectly.


A fun hour of work. I have to say I’m very impressed with the air ducting of the e86. The air box is fed very directly from the kidney grill, more so now with the scoop. I certainly don’t think I’ll ever replace the air box, and even the OE filters are very impressive. The stock intake stack weighed 49.5 grams, the RPI ram air scoop weighs 101.5 grams, a weight gain of 52 grams, again, not bad. We’ll see some major weight loss in a month or so to offset the 425 grams added.

BONUS: I hooked the HD Hero up to the bumper, this time with a sufficiently fast SD card in it, worked like a charm:

Bumper cam was a success, should be a blast when the weather improves. 3.5 degree C start, warm up, then the drive to where I did the work above. It does vibrate against the car a bit which makes some unpleasant noise, I’ll rectify that by adding some foam tape to the back of the camera. Watch it on Youtube for full 720p-goodness.

BTW, I’ve happily moved to using my images to mlkshk, you should too!