Vorshlag BMW E46 M3 CSL - V8 Downforce Monster Track Car ("Chainsaw Massacre")

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FRONT STRUT TOWER REINFORCEMENT

The second common weak point on the E46 chassis, as with many McPherson strut cars, is in the actual strut towers. The sheet metal is a bit on the thin side and virtually all of the vertical suspension loads pass through the strut and into the chassis via these two towers. With a big enough impact you can deform or crack the sheet metal here. It's even worse with sticky race tire loads. Sometimes the towers develop cracks simply from fatigue - again, soft bushings allow for a lot of extra squishy movement, which flexes the metal over time.

Below is a common upgrade we do on many BMW chassis, where we reinforce the tops of the strut towers. The damage shown on the silver E46 M3 track car below is a perfect example of why this work is needed.



This customer saw the tower reinforcements done on the Chainsaw Massacre E46 M3 CSL-clone and wanted the same thing done to his dedicated M3 track car. Good thing, too - when we pulled the strut tower brace off we found a series of massive cracks hidden from view, which you can see above.



The cracks were each "drill-stopped", TIG welded, sanded smooth, then a pair of the BMW E46 reinforcement plates were welded into the towers from underneath - effectively doubling the thickness here. The areas were primed and the car went back on track.

Before the color matched paint arrived to re-shoot the tops of the towers this car was in a track incident. This snapped the right front Bilstein Club Sport inverted strut like a twig, ripped the tie rod out, and broke the control arm and wheel - but the strut tower was fine. I can say with confidence that this reinforcement work saved this strut tower from total annihilation. Doubling the thickness of metal here is key.



Back to the E46 M3 CSL build - Ryan started by pulling the stock front suspension off and out of the way. Then we ordered these stamped steel E46 strut tower reinforcement plates from BMW (Part # 51717036781 ), which are rounded and match the shape of the E46 strut tower from underneath. These are often just slipped in and bolted between the strut tower and the top mount, but we would weld them on for more strength and longevity.



The paint was stripped off the top of the strut towers with our OBX stripper tool. Then the reinforcement plate was bolted in using a fixture and TIG welded around the round opening at the top and along the slotted strut tower holes. There was some prior damage to the lip of the strut tower opening that we repaired and now looks new.



The paint was also stripped from the underside of the tower and from the reinforcement plate. Ryan MIG welded the plate to the tower from underneath with 6 stitch welds as shown. These areas were then covered with seam sealer and primer paint.

SEAT TESTING + STRIPPING THE INTERIOR & ENGINE BAY

In preparation for the roll cage and seat mounting we needed to get the chassis completely stripped and ready for welding. Since this was a "complete build" we tackled the additional work of removing all of the body wiring, tar insulation, and even some unnecessary unibody structure. When you are looking for hundreds of pounds of weight loss you have to chase every pound!



We had Mr Chainsaw test sit various racing seats in our lobby. He liked the Sparco Circuit II seat, which have an integral halo section to prevent side impact neck injuries and high leg bolstering. I also like this seat and have it in one of our shop cars. After we test fit one in this car, I ordered two new seats from Sparco for this build.



The work of removing the dash, wiring, and plumbing from the car to get it down to a bare rolling chassis takes time. It isn't super exciting work but it is all necessary when you are looking to minimize weight as much as we are here. "Just leave the stock wiring harness" might be appropriate for some builds, but not one this extreme.

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Between the engine goals and potential cornering loads (Hoosiers + full aero), a dry sump oiling system was decided early on.



Ryan test fit an oil settling tank we had from another project under the M3's dash, but it just wasn't the right place for this chassis (it will go in the back seat area instead). Then the tedious job of removing the steering column, HVAC box, and dash assembly was tackled. Its all gotta come out for cage work...



This outer dash skin came out cleanly and will be reinstalled after the cage is built. The steel OEM dash bar structure was removed and will be replaced with a horizontal tube, connected under the "skin" of the dash, to joint the front of the roll cage. We will have to replicate a lot of these little hidden brackets to hold the top skin of the dash in place afterwards, but that's how you save more pounds - little bits at a time.



The front windshield and back glass came out next. Since we planned to re-use the front windshield (it was un-pitted and perfect) we hired a professional windshield installer to remove these two pieces of glass. This allows more access to build the roll cage as well as roof panel removal (more on that below).



After the dash structure and skin came out, this giant rats nest of wires (above left) was left behind. Yes the main body wiring harness was completely removed. We would have to pare this down so far that it makes more sense to replace it with a more streamlined, custom built chassis wiring harness. This harnesses was later weighed and it came to 49.4 pounds of wire, just from behind the firewall. This includes the giant cluster of wires under the dash, under the carpet, and in the trunk area.



The engine bay was already partially stripped, as this car had no drivetrain or engine wiring harness when we bought it. But the rest of the underhood clutter had to come out, as nothing OEM was being re-used up there.



The brake and clutch master cylinders, brake booster, ABS module, brake hard lines, and all sorts of plastic panels were removed and scrapped. At this point the engine bay was mostly stripped but even more brackets and panels would be removed later.



Many of the old parts were stored on a wire shelving unit. This way anything we need to re-use is kept together with the rest of the customer's parts. These can be rolled away and stored when not needed.



At this point the interior looks pretty barren. But we're not stopping here. No, NO! WE NEED MOAR!!!

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INTERIOR INSULATION REMOVAL

We were looking for every pound, remember? Next up was the heavy asphalt/tar sound insulation panels stuck all over the interior and trunk areas. These materials are a chore to remove, but it adds up.



A heat gun + a variety of scrapers + lots of elbow grease are the best way to remove this stuff from a BMW. Trust me, we've tried all of the methods - freezing with dry ice, power tools with wire wheels, and sandblasting - and the heat gun is the cleanest, fastest way for the BMW insulation.



17.7 pounds of tar paper came out of the interior and trunk. But it left behind this tacky adhesive goo....



The car still rolls at this point so it was shoved outside and the electric pressure washer was used to blast every surface of the chassis, inside and out. 2500 psi gets all the dirt and grease off the chassis, but it won't make a dent in the adhesive residue.



Over the years we have tried numerous degreasers and petroleum products and found that soaking the adhesive with mineral spirits works like a charm. It softens the adhesive enough to wipe it away, but doesn't damage the paint. Of course we're going to paint this entire chassis inside and out later, but having bare metal during the build process might allow it to flash rust. So .... heat gun + mineral spirits works best on this stuff.

ROOF STRUCTURE REMOVAL + CARBON ROOF PANEL

We still weren't ready to start the roll cage, and needed to do something about the power moon roof that was in the way.


Left: 72.0 pound factory sunroof cassette. Right: AJ Hartman carbon sunroof delete panel at 1.4 pounds

Like most E46 BMWs, this one had a factory retractable sunroof option. The non-M E46 almost always has a sunroof, but a few E46 M3s came without a sunroof - including the CSL.



The 72 pound power sunroof assembly (they call it a cassette) is not only a heavy thing but it gobbles up head room in these cars. We had talked early on about a carbon fiber sunroof delete panel, which we have done on a number of E46 chassis to knock weight out of the roof while gaining 2.5+ inches of headroom (like my E46 330Ci above). Another AJ Hartman pieces that is an easy "bolt-in" replacement you can swap in over a couple of hours.



Since this is a 2003 BMW M3 CSL clone of course we have to use the CSL's full carbon fiber roof panel, duh! We had AJ Hartman make an exact replica of this CSL roof panel, which Mr Chainsaw agreed was more appropriate for this build. Ryan started the roof swap by removing the two roof seam covers, then drilled out spot welds with a small spot weld cutter.



Ryan received some help from our CNC operator, also named Ryan aka: "R3". The two Ryans then finished removing the 100+ spot welds around the perimeter of the factory steel roof panel, prying the glue loose after these spots were carefully cut through. The front and rear glass removal was crucial in this step; the roof came off in a little under 6.5 hours.

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The OEM roof weighed 96.1 pounds (24.1 for panel + 72.0 for sunroof cassette). The new AJ Hartman carbon fiber roof came in at 6.9 pounds, for a total savings of 89.2 pounds - way up high in the roof! Not only did we lose the equivalent mass of a "young adult" the interior gained about 2.5" of headroom. We also had ample access for building the roll cage.



The CSL carbon roof panel went on easily and bolts in place using 4 factory threaded bolt holes, which fit the roof section perfectly. Ryan had to do zero adjustment, custom fitting, or hole enlargement - it just fit.



Once the cage work is finalized and before paint this will be bonded to the body structure just like the factory E46 M3 CSL roof is, plus there are the four back-up bolts as well.

INTERIOR UNIBODY STRUCTURE REMOVAL

The back seat was never going to be used in this build, so to lose some additional weight we looked at the rear seat bulkhead structure and decided to remove it before the cage began. There is a lot of easy weight that can be removed from the back seat, and in our 2001 BMW E46 330Ci we found 63.8 pounds in the back seats + headliner and another 10.4 pounds in rear speakers and a few trunk brackets.



Compared to my 330, this M3 needed an even sharper scalpel this time. We weren't looking to "skin" this car and put it down over a tube chassis or anything, but redundant structures that could be removed would be. There was some easy weight loss in the rear seat bulkhead perimeter structure and rear window "speaker deck" panel - which would have their chassis stiffness more than replaced with roll cage structure. We will make lightweight interior panels to separate the trunk from the passenger cabin.



There were probably another hundred spot welds that were cut for all of these brackets, panels and sheet metal structures in the back seat area. These were cut into small pieces with a reciprocating saw and pried loose without warping or damaging the surrounding structures.



Of course I forgot to weigh all of this before the scrap metal guys came and picked it all up, but it was around 15-20+ pounds of sheet metal in addition to the back seats, interior panels, and trunk brackets that were also removed (with weights noted on our red 330). Now the car was ready for a roll cage!

WHAT'S NEXT?

The intro post in this build thread has already run long, so we better cut it short. Nothing really earth shattering done in this first series of posts, just showing the steps needed to remove weight and add longevity to this E46 chassis. Again, my goal weight guesstimate is 2600 pounds soaking wet with a dry-sumped LS stroker, T56 Magnum, giant wheels and tires, wide body work, full aero, and the required door glass + heater + wipers required for street use.



In my next installment in this build thread I will show the roll cage fabrication work. I will also cover seat installation, custom "low profile" door panel construction, subframe reinforcement, the 8.8" Ford IRS diff swap, and more. We will discuss the classes we are building toward in NASA and Optima, and the rules/performance differences between them.



I tend to show details and pictures of this build and more "in real time" on our Facebook page and in our irregular "this week at Vorshlag" videos on our Youtube channel. Look for those and like/subscribe/whatever it is you are supposed to do there if you want to see the progress on this build sooner.

Until next time,

[rustomatic]

It's awesome. Thanks for posting! Continue!

[YAMATHUMP]

As usual, great build thread. Can't wait to see this in progress.
Keep up the good work.

[Ketzer]

Amazing read! Thanks for putting all that together!