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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Dusty Duster
Dusty Dusterlink
Tuesday, April 28, 2015 5:20 AM
Oh, I love me some straight six engine noise.
Tuesday, April 28, 2015 12:10 PM
The S54 is such a tuned engine from the factory, it is really hard to bolt-on any additional naturally aspirated power. The manifold looks to have slightly helped at the very tip top end of the rev range, but not really that much...3% increase maybe?

As for air filters, correct me if I am wrong, after you meet the minimum flow surface area requirement (which is surprisingly small for most engines), a bigger filter just means you don't have to clean it as often...i.e. no additional performance benefit.

Forced induction seems to be the way to go when you really want make the dyno numbers on those cars.
Pablo Mazlumian
Pablo Mazlumianlink
Tuesday, April 28, 2015 6:59 PM
Hi guys, thanks for reading!
@Dusty, indeed!
@cartechs, agreed. These cars are rung out well from the factory. But they still surprisingly respond well to upgrades. You have to remember that we started this all with 290whp, and getting close to 330whp (I'll hit that if I put the old alt pulley on and old wheels) is a 40whp increase with just bolt-ons and software. The engine's been untouched internally. The biggest gain you'll get with the airbox is by also doing cams. There are guys making 365-380whp with this combination(!).
I experienced this with my father's E46 SMG as well, which is what originally convinced me to get after an E46 M3 for myself. With his car I started at 289whp, and by the time I was done with full exhaust, Stage1 Macht Schnell intake (panel filter, no cone) and a software upload, we were at 323whp on 91 octane in CA. Crazy gains for intake and exhaust on a pretty high-strung car.
The main reason I chose to go with the larger air filter was aesthetics, and the piece of mind that there is no restriction from all this air filter allows. It's one honkin' big mama.
Thursday, April 30, 2015 1:30 PM
So is the next mod cams? :D
Thursday, April 30, 2015 6:58 PM
Anyone have a link to a good E36 in car video for sound comparison to the E46?
Pablo Mazlumian
Pablo Mazlumianlink
Thursday, April 30, 2015 7:34 PM
@brian: Don't know yet. Would be nice! :)
@538: I've only got a couple of old vids of my previous cam'd E36 M3 and E36 M3 turbo, as well as another supercharged car I'm "friends" with (actually have that car for this weekend too!):

E36 M3 with Sunbelt cams (fast fwd from 1:00-1:45, sorry about that):

E36 M3 with V2 SQ supercharger:

E36 M3 with top-mount T66 Turbo:

sorry if not what you're looking for.
Thursday, April 30, 2015 10:14 PM
Videos are perfect! The E36 sound sounds a little lower in tone, but I think i prefer the E46 based on the videos. Thanks for that.
Friday, May 01, 2015 7:53 PM
Man this thing is beast mode for real. Strangely it doesn't have the same rip as other CSL plenums I've heard though. But it all works. 40WHP on an S54 with just bolt ons and software is impressive as hell too. With cams this thing will be downright scary. All it needs besides that... maybe shorter gearing? Seems to drop a ton between gears.
Pablo Mazlumian
Pablo Mazlumianlink
Friday, May 01, 2015 8:30 PM
@538: glad to hear! You're welcome.
@CTK: It is a fun car to drive indeed. With cams (and of course sc'r) this car would be just nuts but I'm contemplating still.
Regarding gearing, it actually is too torquey for the first two gears (2nd gear will hook up if it's over 60F). If you're referring to the noise drop in the coming-at-you vid, yeah the revs drop because I redlined 1st gear spinning the tires, but when they caught the car wasn't actually going that fast. I just did it for the sound, and so you could hear the midrange. If you look at the speedo video however, especially of the one I did with the AEM Infinity launch (link below), you'll that a 1-2 and 2-3 shift at redline puts me right at 6000 RPM in the next gear, while 3-4 puts me nearly 6500 RPM. So it's got plenty of revs! And if I would ever increase the torque/power with cams and/or supercharger, I'll probably regret going shorter then especially lol.

https://www.youtube.com/watch?v=MPlWRLgbzD8 (this vid is pre-airbox btw)
Monday, May 04, 2015 2:39 PM
How do cam changes integrate with the dual VANOS control? Can VANOS just be manipulated to simulate cam changes?
Wednesday, May 06, 2015 3:35 PM
Nice gains! Might be interested in picking one of these up now, especially since Castro isn't too far from me. It's a bit ugly compared to the "CSL" ones available but so what. I like the idea of matching the OEM wrinkle on the VC or on the stock airbox plenum.

@cartechs with the S54 VANOS you couldn't change, say, valve lift or duration, only essentially the cam "centerline" for both intake and exhaust, although you get 60* movement on intake and 45* on exhaust. Therefore there are still pretty significant gains to be had even on an N/A bolt-on engine with a cam change, like a Shrick 272/280, 10-15whp or so with almost no loss of low or midrange. They're also $1,400 for just the cams.
Wednesday, September 23, 2015 12:03 PM
@Pablo Mazlumian Were you able to to keep the radium engineering catch can while using the castro airbox? I've been following the build and love it, keep up the motivating mods!
Pablo Mazlumian
Pablo Mazlumianlink
Thursday, September 24, 2015 8:48 AM
Thanks, and yes the catch can is still on there!
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