Project Update for August 15th, 2017: I started writing this in July and got buried with other projects and work. We have accomplished a lot on this car since the last update and I will try to show as much as possible here. I will go over the custom fuel cell + fuel filler neck and oil tank, along with the mounting structure and fire proof enclosures for all of that.
We also will cover the aftermarket front bumper cover install as well as the structures built to hold that and twin oil coolers. There were Lexan rear side windows and back window added. And we built some really big ass flares to cover the big ass tires. Lets touch on those
first!
WIDE BODY FENDER FLARES
This section could be huge, but go read the flare section in my
June 9th post in our E46 330 build thread, and we can all save some time. In that post I cover the flaring options and installation techniques, and even reference this car's flare job.
As I showed last time, we are building this E46 M3 around what I call "GOD'S TIRE SET" - a 335mm wide front and 345mm rear Hoosier A7 DOT tire setup. I've run these tires successfully on our
TT3 Mustang (above left) and even briefly on our
92 Corvette (above right), and I'm building my new
C6 Z06 project around the same set of tires too. I say if something works, stick with it!
It took me decades of dabbling in "wide tires" before I managed to work my way up to this mega-sized set. We progressed the wide wheel/tire thing on our STU classed BMW E36 M3 in 2006 (running 18x10" wheels under stock fenders), then went to 315mm tires on the Alpha E36 LS1 (above right). Our
GRM Challenge winning E30 V8 got 18x11" wheels and mega-sized box flares after that.
We were already stuffing 18x10" wheels and 285/30/18 tires under BMW E46 cars ten years ago
The most tire you can fit under stock E46 M3 fenders is roughly a 285mm front and 315mm rear. I've run 285mm square on many E46 M3s and have installed M3 fenders on non-M E46 models to be able run that tire size. But that's just not wide enough for a
powerful road course car. I always ALWAYS want to run the widest tire that "a driver can afford", and this car has the power and the potential of very few, so it deserves THE BIGGEST.
Last time we had fitted the 18x13" wheels and 335F/345R tires, and they obviously had a lot of poke past the M3 rear and non-M front fenders we had stuck on the car (this chassis was purchased without front fenders). Instead of buying then just cutting up valuable OEM E46 M3 fenders we kept the ~$35 front fenders from my old 330 on there to cut and build upon. Before we started cutting metal it was time to break out the craft paper and scissors...
FLARE DESIGN MOCK-UPS
The front mock-up flare (above left) was designed and shaped first. We were looking for some specific aero improvements that help reduce drag (covering the front of the tire) and help create downforce (evacuating the wheel well from behind). We went over several vent shapes and decided on an extended width fender face that is open at the leading edge of the door. The rear flares would follow the same mantra but it was later revised a bit. And while aero takes precedence, the style is important for Optima D&E judging, too. Nobody wants an ugly race car.
MAKING ROOM FOR THE TIRES - REAR
Anyone can slap on a set of pre-made "flares" fairly quickly, and the Stance Crowd often does this without doing the necessary cutting and fabrication work underneath. The real work is in the chassis clearancing - making room for the tires to travel in the "bump" direction (up) as well as allowing the front tires to "swing" while steering. This is often why I recommend a fabricator do the initial work on any custom flare installation, and not a painter. Sometimes paint and body shops don't understand the dynamics of how a suspension works on a street or race car. They also tend to use a bit more body filler. To keep weight to a minimum and allow for maximum tire clearance we tackled the custom steel flares in-house on the E46 M3 here. We will do a complete track test before the flares ever see any bodywork/paint, too.
Left: Making room for tire clearance before the flares go on is key. Right: As is thorough testing before paint!
Cutting and welding to make room for mega wide tires is difficult to do correctly and retain a waterproof and strong unibody once you are done. I've seen some janky cutting done under some flares and they leak water inside, smoke, fuel, fire, etc. These sections that are modified really need to have an air tight seal to be FIREPROOF when complete, and this isn't something you can afford to half-ass.
Normally on a unibody car cutting the rear fenders and merging them back together is the hardest part - and this car wasn't any easier than normal. What we do is take the wider tire & wheel, remove the rear spring, and compress the rear suspension into the bump stops (ie: "full bump travel"). If the car's inner structure allows it we cut the outer fender sheet metal (sometimes 2 layers) all the way above up to clear the top of the tire at full bump.
This 345/35/18 Hoosier is a really tall tire (
26.8" tall) but it was still possible to get full tire clearance and not cut into the rear inner fender beyond the centerline of the tire. We were prepared to do that, if necessary. This car needs about 3" of bump travel with the MCS RR2s and it now has it. Due to aero loading it will have some rather firm springs on track, so we might never see 3" of bump in actual driving.
continued below