Project E46 M3: Part 11 – Castro Motorsports air box installed and dyno tested!

We install and dyno test a Castro Motorsport CSL-style intake plenum on our E46 M3 at Modified by KC.

Project E46 M3: Part 11 – Castro Motorsports intake manifold installed and dyno tested!

We test our intake plenum on MKC’s dyno, plus show you a couple of other cars that MKC has been working on, including one of the baddest BMW 335s in the country!

by Pablo Mazlumian

When the E46 BMW M3 was released in 2001, it was rated at 333bhp and 262 lb-ft of torque by its Munich headquarters.  The E46 M3 was a huge step-up from its predecessor, the US-spec E36 M3, with 93 more bhp from just 95 cc more displacement.


Here’s a look back at our bone stock E46 M3’s engine when we started this project.

However, there was another version of this M3 that we didn’t get to play with.  BMW also released the M3 CSL, which stands for “Coupe Sport Lightweight”.  It pays homage to the early 70s E9 BMW 3.0 CSL “Batmobile” that was so successful in racing.

The E46 BMW M3 CSL was given a 360bhp engine that peaked at 273 lb-ft of torque.  That may not sound like a lot by today’s crazy power standards, but let’s put it into perspective.  In that same year, the 4.6-liter Ford Mustang—which was indeed sold as performance car and not a tractor—was rated at 100bhp less!  And it also only made 11% more torque with its 43% extra displacement.  Even the supercharged 4.6-liter SVT Cobra had only 30bhp on this little normally-aspirated 3.2-liter.  The numbers for the CSL were staggering. 

To help achieve this power level, the CSL engine was given more aggressive camshafts, larger exhaust valves, and a much larger intake plenum than the base M3.  With a myriad of BMW tricks, the car was also lightened to just 3,054 lb, which was roughly 10% lighter than the standard M3, and with a 50/50 weight distribution to boot!  The car was so good that it was reportedly only 2 seconds off of the Nurburgring time achieved by the $150k 450bhp 4.4-liter M3 GTS, another car we didn’t get.  It’s too bad only 1,358 CSLs were ever built.


This is what a factory-stock BMW CSL engine bay looks like.  Do you notice something very different?  Check out that carbon intake plenum.

The BMW CSL spawned an aftermarket war of carbon fiber CSL-style airbox replicas.  When most companies decided to stick with carbon fiber as their choice for raw materials, they left most E46 M3 enthusiasts no choice but to keep their factory plenums.  After all, not everyone had four to five grand to spend on an airbox. 

As we continue to modestly upgrade our E46 M3, we’re enjoying the performance of this little 3.2-liter that continues to put out around 320 wheel horsepower, and over 260 lb-ft of torque (which equals the E90/92 M3 V8 engine's peak torque!).  That’s crazy performance from the S54’s stock 198 cubic inch long block.  We’d love more performance—especially with a CSL-style airbox—but this next step has been eluding us for years due to the cost.  And then along came Castro Motorsport, and from our own back yard.

Located in Southern California, Castro Motorsport is an outfit dedicated to providing service as well as custom work on BMWs meant for both street use and racing.  They’re not new to any wild projects either.  In fact, they’ve got a racing E46 M3 sporting an LS7 V8 from the C6 Z06!

So why are these guys important to our project?  Well, not only do they guys make an even larger airbox than the CSL unit for the E46 M3, they’ve also cleverly fabricated it with fiberglass, which is significantly less expensive to produce, giving us poor-folk a viable alternative to the pricey carbon fiber.  We’ve installed Castro’s intake plenum on our car, and we’re excited to share with you our testing results.  We've also got a couple of quick video clips of the sounds on Page 10!


Here’s a quick look at the Catro Motorsport’s air box compared to a stock E46 M3 manifold, which is still rockin' the Macht Schnell silicone boot we tested in Part 1 as part the MS intake kit.

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