BMW E46 GTR Build Powered by a S85 V10

Jun 3, 2020Builds0 comments

Everyone starts somewhere different. In our case, we started with an offer for a S85B50 V10 that had developed the well-known “rod knock” issue. Without hesitation, we took the offer and began with the very first steps of building something fun and worthwhile. After browsing the internet for about 2-3 weeks, we came across a clean title E46 coupe shell for the astronomical sum of $200. PERFECT!!! After we dropped the oil pan on the S85 we did find some damage…but luckily nothing to do with the rods. Still unfortunate, we learned that the secondary oil pump had failed and seized the motor.

Tear down of the rolling chassis began the following morning, and although the car was already pretty bare, there was still plenty of clean up work to get it ready for the first first steps of fabrication. We already had all the essential M3 suspension components, including the rear carriage and differential. We removed every single wire and cleaned up all of the factory sound deadening, which, by the way, required its own special level of patience.

GTR Build Essentials

Now we have a motor that needs parts and rebuilding and we have a chassis that needs an impossible-to-source body kit. So where do we start? The motor seemed to be the most logical place. Much of the engine needed refinishing and that meant throwing a smattering of brand new parts into all ten cylinders. We chose to replace the entire valvetrain, replace the rod bearings, refinish the crankshaft, refresh the heads, and…..delete the VANOS? The decision to delete the VANOS was in order to make this car as reliable of a track car as possible. Much of the S85’s VANOS components are expensive and prone to failure, so we figured we’d make them a non-issue. As the car would have a custom wiring harness and ECU solution, tuning would not be an issue. We mated the motor to a 6 speed manual gearbox from an E9X M3, as well as a fresh S85 clutch and flywheels.

Visions of greatness

You would be hard-pressed to find a car fanatic that doesn’t know the E46 M3 GTR. The wide, P60B40 V8 dominated ALMS in the 2001 and was so fast that it was banned outright only a year after its inception after failing to meet homologation requirements. It was still campaigned internationally through much of the early 2000s in other series. The car was also the cover of Need For Speed: Most Wanted. Needless to say, the M3 GTR had a massive reputation, backed by its staggering presence.  With this in mind, we decided that we would have to pay proper tribute to the original chassis that captured out hearts. The PTG spec 9/11 livery car is one of our favorites, with its distinctive red, white and blue livery. Unfortunately, it is all but impossible to acquire the original body kit that those cars featured and we felt that none of the other kits on the market accurately recreated that look. No matter though, we’d just have make our own…from scratch…with nothing to go off but pictures. Doesn’t sound too hard right?

Well it is. There is a lot that goes in to building a body kit by hand, so we decided to start from the wheels out. We purchased a set of BBS E29 centerlock faces from a Porsche GT3 Cup. Here’s where things got tricky. After a lot of consideration, we decided that we would pursue a 5-lug mounting solution rather than the original centerlocks, as we felt the stud and nut option was more reliable and livable in the real world. Instead of discarding our beautiful race wheels, we opted to send them out and have them carefully redrilled to a 5×120 bolt pattern, all while taking into consideration the effort that BBS had undergone to maintain significant weight savings on the backpads. We then sourced lips and barrels so that we could run 10 and 11 inch wheels for the front and rear, respectively. The 18 inch E29s have optimum backspacing and barrel clearance to fit the new Brembo GT 6-pot calipers and a 345mm two-piece floating rotors, perfect for bringing a 500+ horsepower track car to a halt.

From the ground up

Once we found an appropriate wheel and tire size for our build, we started forming the flares around the newly widened track. Using a myriad of detailed images that we had gathered from the PTG M3 GTR, we began with a foam base and started to shape the flares around the massive tires. With a 285 in the front and a tall 305 R-Compound in the back, the signature flares of the M3 GTR came to vision. We took care to utilize the factory fenders and bumpers while building the kit, so that mounting them to another car would be as effortless as possible, while also conforming to the accuracy of the PTG kit as best as we could. We also took care to improve on what we found to be some shortcomings in the original factory kit. Most of these were just nitpicks with the fitment and symmetry of the original kit that we noticed.

After creating a rough shape out of foam, we used fiberglass and resin to create a mold of the flares. The front fenders were sent out with the flares, to make the fenders fit as accurate to OEM as possible. The flares are roughly 60mm wider than the stock car on each side, allowing you to push the track width far out and easily run wide wheel and tire setups without any worry of interference from suspension or the body.

Replace Everything

Back on the chassis, we chose to refurbish the entire M3 suspension setup with semi-solid or monoball components where appropriate, which was basically everywhere, and also freshly refinished the retained original components to factory specs for OCD’s sake. As this is going to be a track car primarily, we were more concerned with eliminating the slop and play that the factory components are known for. Many of the new components also allow for increased adjustability of camber, caster, toe, and roll-center correction. The goal was for this car to handle just as monstrously as it would look. 

Simplify, Add Lightness

Quite a few things differentiate the factory E46 from the PTG racecars. Much of the weight-reduction on the race cars comes from shaving the brackets and mounting points that much of the original interior mounts to. The original wiring harness also contained a significant amount of extra electrical connectors for the factory auxiliary components like speakers and lights. All of this would be scrapped, as it is completely unneeded for a race build. We had a custom engine harness fabricated, and ran simple wiring and relays for the turn signals and lighting . We also opted to cut out the factory battery box and spare tire tray, replacing them with light weight aluminum plates. We also cut out the entire rear seat and deck area, which proved to be a substantial amount of weight. The factory doors were completely gutted of their internals, and the maximum amount of material was shaved from them without sacrificing their original usability and structure.

With all this cutting and shaving, we decided that we needed to do everything the proper way. In proper motorsports spirit, we took the factory dashboard and replicated it in beautifully woven carbon fiber. Weighing in at 6 pounds, and fully customizable, the carbon fiber dash is a true race-inspired piece. This is a huge advancement for the E46, as there are no other available aftermarket dashes that accept the factory trim or mount to the factory locations. The dash fits amazingly, and will accept the center factory vents and cluster with some modification. 

Safety first

One of the most important aspects of building a racecar is building a proper roll cage and ensuring the car is safe on the track. There are quite a few places that are important to reinforce on the E46, especially the rear shock tower mounts and the subframe mounting points. Never ones to leave anything halfway, we opted to have a full FIA-spec roll cage, built in the style of the original PTG car. We also mounted a set of CA Tuned pneumatic race jacks at all four corners of the car, for those quick wheel and tire changes. Hundreds of pounds were stripped from the car during the race preparation, including the original sunroof. We opted to fit the Lang Racing carbon fiber roof, which was approximately 50 pounds of weight savings at the most critical spot of the car.  

Exhausting work

With a powerful motor, comes a lot of flow. We have heard a lot of S85 exhaust setups in our days. Multiple brands of mufflers, headers, ​straight pipes, resonators, the whole nine yards. A lot of them sound great, others sometimes not so much. But one thing is certain in our minds, the tone produced tightly bundled original headers was crucial to retain. The original headers also provide tons of engine bay clearance, minus the massive catalytic converters, so we chopped off everything behind the pinch collectors, and fabricated a whole new setup. In true M3 GTR fashion, we redirected the 3 inch exhaust all the way around the wider E92 transmission and out the passenger side floor pan and side skirt. The fire-breathing side-exit exhaust is a signature feature of the M3 GTR, and was not something that we were willing to omit. The car will later get a custom muffler box to tame the volume, but for now it’ll stay vicious and wide open. 

Taking Shape

Getting the pieces ready for the mold process is one of the most difficult parts of the entire process. Many hundreds, maybe even thousands of hours were spent refining the edges, symmetry, level and overall fit and finish of the kit. Without much to go on other than pictures, many areas were done and then redone to achieve the best possible results. We are aware that parts of the kit are…. polarizing…. to say the least, but for the sake of accuracy we retained even the strangest of features. We decided it best to leave some of the features off of the final product, most notably the cut panels on the back side of both front and rear flares. These can be easily be cut added in post if desired, but are designed to increase or decrease flow within the fender for aerodynamic and cooling purposes as desired. Overall fitment is tight and as close to OEM as possible. for a full widebody kit.

Heart of the Beast

Over the past two decades, the aftermarket has found that the E46 Chassis has a substantial amount of space in the engine bay. Many swaps have been done on them, but many try to cram the largest engine in possible. Even BMW took this approach in the early 2000s, cramming the S62 M5 engine and later the P60B40 motorsports engine in to E46 M3 GTRs. Still, one of the most coveted engine swaps of them all is the S85 V10 from the E60 M5 and M6. Fitting the 5 liter engine into the engine bay of the M3 is no small feat. Impressively, the S85 is not much heavier than the iron S54 lump normally fitted into the E46, and is significantly lighter than the S62. The motor sits low and far back, allowing the tangled headers to clear the frame rails with relative ease. The steering rack needed some minor adjustments to fit the motor properly, and the engine bay had to stripped clean to make sure that the heads and the intake manifold of the wide-angle V10 would not contact the strut towers or the hood. Custom engine mounts were welded to the subframe and solid delrin pucks were used as bushings to support the engine. Overall, the swap is fairly straight forward, although not necessarily easy. Quite a few sacrifices would have to be made for the swap to work on a street car, and though it didn’t prove to be an issue on our build, it’s certainly possible. 

Inside The Cage

As beautiful as the ten-point M3 GTR-spec roll cage was in all of its glorious raw steel, they don’t stay looking that way forever. To keep the amount of invested effort in the stripped interior to a minimum, it was quickly sanded and prepped for a primer-sealer. The raw primer-gray coating inside the car really reflects just how far this build has come. Evidence of the car’s origins are nowhere near as obvious as they once were. Gone is the entirety of the sound-deadening, scraped off in hours of painstaking labor. Brackets and clips are trimmed or removed where necessary, and everything is beautifully smooth. Some of the more aggressive openings are welded shut, or in the process of having custom covers made. It is a total transformation, appropriately accurate to the car that we have drawn our inspiration from. 

A Heart of Gold

It should come as no surprise that we draw our inspiration for this build from BMW Motorsports heritage. One of our favorite looks ever comes from the M12 series of engines, which were featured prominently in 1970s BMW race cars and Formula cars. The motor has a distinct gold-on-black scheme that is striking, to say the least. While the S85B50 doesn’t have the trimmed race ready look of the M12, we knew that we could take some steps to improve the aesthetics while still highlighting the unique nature of BMW’s only V10 streetcar engine. We formulated a custom process to get the deep gold color that we were looking for, and began to work prepping the engine for paint. After careful, meticulous masking, we set to work laying down the black base coat on the entire motor. We followed up with our bespoke gold color on the top half  of the motor, including the valley and the heads. The satin black is carried over on our signature velocity stacks, as well as the modified factory headers to replicate the M12’s look as best as possible. We also made some unique modifications to the other parts of the motor to streamline it’s design and give it a more simple motorsport look, but you’ll have to check those out for yourself when the car is unveiled. 

Maximum Downforce

It wouldn’t be a proper race car without a properly gargantuan wing. In order to get the dimensions perfect and make some truly massive downforce numbers, we teamed up with AJ Hartman Aero to produce a wingblade with the dimensions as close to the real GTR as we could determine. Spanning 66 inches across and 14 inches in chord depth, the wing is capable of generating nearly 2000 pounds of downforce at 190 miles per hour with their gurney options. Take that in for a second… 2000 pounds of downforce, a solid ton. AJ Hartman also accommodated our custom upright width requests so that we could properly replicate the narrow upright design of the PTG-spec GTR. We set about fabricating a set of custom uprights, which pass through the decklid skin and are mounted to structural braces that are welded to the inner trunk surfaces. This allowed us to create an immensely strong bracket system without adding excessive weight while allowing access into the trunk for fuel cell maintenance.

The Art of Refinement

After all of the time and work put into the work of the kit, it is important to ensure that everything will work together. This includes the functions of the car like steering, compression, necessary trimming, and the fitment of original parts against the new body pieces. This is the stage where we currently are, focusing on dialing the car in before final production. As of August 2019, the bodykit has been produced and is available for purchase. Additional parts are in the process of being designed and fabricated. The entirety of the kit is be available for purchase on an as-ordered basis. Current lead time for the kit is 6-8 weeks. 
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