F82 M4 GTMore
BMW competes in international racing with the F82 M4 in the GT4 class (and soon to be in the GT3 class). We were among the first US teams to receive the GT4 and promptly put it on the podium. As a Customer Car from BMW Motorsport it's an outstanding machine. But in motorsport with multiple types of cars there are compromises to level the playing field for everyone (aka Balance of Performance). In the case of the M4 GT4 that handicap comes mainly in the form of a power restriction. There are five allowed power levels for the M4 when it competes in GT4 trim. When allowed, the highest level is about the same as a stock M4 GTS - 500hp. Looks can be deceiving but our racy GT4 is often slower in a straight line than our tuned street cars. The Porsches have to keep up somehow.
So that led to the question, "What can a GT4 do if it was un-leashed? How much faster can we make a street M4 than our GT4 race car?"
Click to jump:
Our subject is a 2015 F82 M4 in Mineral Grey with DCT and Carbon-Ceramic Brakes. The car was completely stock when we received it and had covered just 53,000 miles. First stop was the workshop where it got a complete fluid change to Red Line Oil and then onto the dyno (421whp, 415wft-lbs).
M4 Aero Upgrade, Part 1 - The Wing
You won't get anywhere these days without big aero. The GT4 has a modest but functional rear wing, dictated by aero parity with other competitors in an international GT4 series. Without these restraints our only considerations were functionality and, frankly, aesthetics. Anyone can plop a super-sized wing on their car and look racy. That's never been our approach. This is a bespoke, chassis-specific, and dedicated race wing for the F82 coupe profile. Also as a fresh sheet design we took advantage of the swan-neck configuration to maximize efficiency and surface area.
The swan-neck mounting minimizes obstruction and drag on the underside of the wing and takes up less real estate overall than traditional pedestal uprights. This wing comes as a complete kit which is a direct bolt-on for F82 coupe models (unlike generic elements that require hours to make both legal and functional, or unattractive adaptor blocks). Additionally, using a proven motorsport airfoil profile modified for our specific application, the efficiency is much higher than production-based spoilers including Lightweight/Motorsport reproductions and the Chinese replicas of Corvette wings with upturned, drag-inducing ends.
We made this as a complete kit for a standard F82 trunklid as well as an upgrade for GT4 models that no longer need the homologated wing.
M4 Aero Upgrade, Part 2 - The Splitter
Any rear wing must be balanced with a front splitter and we stepped up our game for the GTMore. Again, the GT4 is rules-restricted on the shape and size of the front splitter. We had to go bigger.
The GT4 splitter follows the contours of the front bumper (per series rules). Which means it gives up surface area at the outside edges. An un-restricted design would have more surface area as the profile would be consistent across the entire front edge. That's a given on any motorsport splitter. The GTMore splitter is not hugely deeper at the center point of the car (only about an inch) but it maintains that leading edge across its whole width - at the outer edge it's about 3.5" deeper than the GT4 piece.
The shape of this splitter is where the true magic happens - and where our aero expertise is tangible. This splitter is not to be dismissed as just another flat piece of carbon. There are plenty of "undertray" splitters out there for less money and performance. This is a true air foil with a more efficient profile on the leading edge than the GT4 splitter. It also has brake ducts and large diffusers built in on the underside. This splitter is all about managing airflow on top and bottom to maximize the full surface area.
GTMore Brakes Part 1: Pagid Track Pads for BMW CCB
This is not our first project car with carbon-ceramic brakes but it's the first one where we are pushing all systems beyond their limit - and the brakes are no exception. In our first track outing with the car we confirmed some glaring deficiencies with the stock carbon brakes but also tested and adopted a solution.
The Carbon Ceramic system (CCB) is futuristic technology with a lot of positive attributes - lower unsprung weight, longer service life, and minimal unsightly brake dust. The downsides are extremely high replacement cost and a lack of heat capacity for hard track driving. We knew going in that the stock CCB pads are formulated for street driving, which is what 98-99% of CCB use will be. Like traditional pads, CCB pads perform well within a certain temperature box. Step beyond the walls of the box and trouble reveals itself. The issue with CCB pads is that the friction material overheats and instead of forming resistance with the disc the material smears over the disc surface. The resulting loss in friction will make the pads and the discs essentially worthless. Since the CCB discs cannot be turned or machined this trouble can cost you a ton of money - replacement discs and pads can run over $15,000! And will limit your speed and performance the next time you want to take your CCB to the track. It's important to clarify that this is not a defect in the CCB rotors or pads. We took them outside of the limits they were designed with. We're actually big fans of the CCB package because the pros outweigh most of the cons.
The Pagid RSC pads have been designed specifically for carbon brakes. Like traditional pads the material has been formulated to work in a higher temperature zone without a loss in friction. The Pagid pads are more stable at the temperature levels we are used to seeing at the track. This extra capacity provides the crucial buffer between excellent on-track performance and a carbon ceramic paperweight. We used the RSC1 compound in the front and rear which were very compatible with the stock BMW CCB rotors. Having a more appropriate pad for track use will make you more confident in the braking zone, better modulation and release, and consistently better stopping power. And you can use the RSC1 compound for limited street use, avoiding a pad swap at the track.
Our Motec data system backed up what our driver was experiencing at the VIR long course. We have two excellent braking zones from high speeds - turn 1 and turn 14. Our data was recording brake system pressure, system pressure with ABS, wheel speed, vehicle speed, longitudinal G force, and other parameters. Most interesting to us was the wheel speed and the ABS intervention. We knew the Pagid brakes were going to stop better than stock pads but we also wanted to ensure proper ABS operation. The stock pads beyond their limit were causing dramatic ABS operation - the ABS was cycling in a desperate attempt to keep the brakes at that threshold of lockup. The Pagid data was much more stable and consistent, allowing the driver to brake later with just as much pedal pressure and less ABS intervention. We should mention that we did not change the DSC settings or reflash the DSC module with different software. The RSC1 compound has excellent compatibility with the factory BMW DSC strategies.
GTMore Brakes Part 2: CCB-to-Iron Disc Conversion
While we believe we have overcome the biggest limiting factor on the stock CCB on the track the fact is these are still consumable parts. And anyone that tracks their car regularly is aware of consumable costs. For a set of CCB rotors and pads it's about $16,000 (or the price of a good E36 M3 track car). Traditional iron brakes are much less cost and provide about the same performance, as we discovered by swapping brakes at the track and recording the data.
We swapped to Giro Disc iron rotors and Pagid race pads for the stock CCB caliper. Braking performance, measured by G force and brake pressure, was virtually the same with the iron brakes. We did not see any loss in braking performance in our back-to-back testing of carbon-ceramic vs iron. And because the pads were not giving up under the heat we had more confidence in the car. Our pro racer behind the wheel can feel the difference between the carbon and iron discs. The CCB saves 15lbs per corner and that makes an impact in MOI and performance.
Weight does matter but is it worth the enormous additional costs? For every pair of CCB rotors you can buy a pair of assembled two-piece iron rotors plus 9 pairs of replacement rotor rings! It's very common for Porsche and Corvette owners to swap from carbon to iron discs for any track use and all indications are that the BMW CCB are no different. Put your carbon discs in storage for when the time comes to sell the car.
In a F8X CCB conversion we keep the original CCB calipers and only swap the rotors and pads. The calipers are not specific to the CCB brakes - they are actually the same as the M2 Competition and very similar to the F10 M5. But they get the gold finish for CCB use. Every other part of the caliper is the same between CCB and iron - caliper seals, brake master cylinder, brake booster, lines, etc. We use the rotors from the M2 Competition - 400x38mm in front and 380x28mm in back. As a track upgrade we like the Giro Disc 2-piece rotors because they are lighter than OEM iron rotors, have a better vane structure and premium metallic content, and the iron friction rings can be replaced separately. You can also use factory OEM M2 Competition rotors. Note: because the rotor size stays the same you must still run 19" front wheels. If you want to run 18" wheels you must switch to a smaller rotor, which we'll cover in Part 3.
You just saved $14,000 that you can put towards something more important... like safety gear.
GTMore Brakes Part 3: Alcon Racing Brake Kits
GTMore is a dedicated track car and will consume items like brake rotors, pads, and tires just like any other track or race car. As much as we like the weight savings of CCB we just could not absorb the replacement cost of carbon discs so we switched to a traditional iron. This also allowed us to run a more standard 18" tire and wheel that offered more tire choices.
We approached several major brake suppliers but only Alcon could provide us with the highest-quality materials and workmanship. The GT/Touring Car calipers are forged from aerospace-grade billet aluminum in the UK. Dry weight is just 7.37lbs without pads. Forged two-piece calipers are extremely stiff, which translates into greater confidence in braking and optimum performance. One huge selling point for us was these calipers take extra-thick pads - 25mm in front and 20mm in the rear. Thicker pads have more heat insulation, last a long time, and are vital for endurance races. The brake rotors are cast and machined in the US from a proprietary iron with high carbon and copper content that has exceptional thermal stability and high strength from low weight. The turbulator vane design pumps air through the disc much more efficiently than straight or curved vanes. The discs are truly impressive in person with extra-meaty 36mm thickness on the front (most aftermarket BBK are only 32 or 34mm).
We worked directly with Alcon to get this new kit on the market that met our own GTMore goals but also as something we think our customers would value as well - a true racing brake kit with premium components not found on mass-market big brake kits.
M4 Engine Upgrades
We did all of the brake and suspension work on GTMore first, leaving the engine alone aside from some software tuning. But for 2022 we are planning a lot more engine upgrades to take GTMore into another performance realm. Stay tuned here to read more about our experiences....
Oil Overfill Kit - Level Sensor and Spacer Kit
M4 S55 & DCT Complete Fluid Change
It's pretty much universal that when you buy a used car you change the oil. Especially true for cars that have just surpassed their factory maintenance plans where - if you were lucky - it got a few engine oil changes, brake fluid flushes, and radiator coolant top-offs. It did not get transmission or differential oil changes under the BMW maintenance plan. If you want to invest in the long-term health and performance of your new purchase a complete fluid replacement is a smart move. Here are the fluid products we used in our new-to-us F82 M4.
Engine Oil - Red Line Euro Series 5W30. The Euro Series is a special formula intended for European makes. It's a high-performance Group IV/V full synthetic with a high ZDDP content but low SAPS value. In plainer English it's more compliant with modern technology in Euro cars, especially turbocharged BMWs. As a true full synthetic (not marketing) it has extremely high shear resistance at high temps and does an excellent job of coating metallic surfaces. The low SAPS makes it more compatible with modern catalytic converters that should not be using older high-ZDDP engine oils. The Euro Series is the best option for a high-performance turbo BMW.
Coolant - Red Line Supercool pre-mix. This is a new coolant/antifreeze formula from Red Line that ticks all the right boxes for us. It's compatible with factory BMW coolant, including being Nitrate, Phosphate, and Silicate-free. It's pre-mixed with distilled water. It's pre-mixed with Red Line Water Wetter. And it has a longer service life than factory fluid.
Transmission - Red Line DCTF. This was a no-brainer for us as we used it in our factory M4 GT4 race cars and it dropped the transmission temps right away. When temps get high the shift time and performance suffers, even to the point of faults and limp mode. The GT4 has slightly improved cooling and capacity over the street car but it needs all the help it can get and Red Line DCTF helped us out a lot.
Differential - Red Line 75W140. Just like with the transmission fluid, the properties of the gear oil also help reduce internal diff temps. The 75W140 grade is the same as the factory oil weight but the quality of the base stock is much better.
Brake Fluid - Red Line RL-600*. Brake fluid should really be changed completely every two years. And more often if it's a track car. The factory fluid is DOT4 so it's pretty good out of the bottle. Red Line RL-600 is a Super DOT4 that actually exceeds DOT5 specs.
* - the factory fluid is a low-viscosity weight, meaning it's super thin. For any street use we recommend an OEM low-viscosity fluid such as Pentosin or Ate. However, for track use this fluid becomes too thin when it gets hot so we start out with the traditional normal viscosity RL-600 and let it thin out as it gets hot. These normal viscosity fluids can be used on the street but it's not recommended.
Red Line Fuel System Cleaner. Any car regardless of mileage can use an occasional fuel treatment. An internal combustion engine leaves carbon deposits throughout the system and that will have detrimental effects at some point. An occasional cleaning will break up carbon deposits (to a certain extent) and improve efficiency and performance.
M4 18x11 Square Fitment & Suspension Upgrade
Stock control arms with coil overs will allow 285-295 tires on 18x10 or 10.5" wheels. But the big grip comes from 315 slick tires and that requires 11.0" wheels. It's always been easy to fit the 11.0" on the rear. But there is just not the right combination of alignment and room on the front to clear the 11.0" wheel on stock bodywork. BMW did it with the GT4 race cars by using custom tubular control arms, an eye-mount front strut, and camber plates. The wheel is an ET30 with a massive 32mm spacer (leading to an effective offset of -2mm). Given the mission statement of the GTMore build we had to have an 11.0" square set too.
The existing tubular control arms on the market work great for 18x10 or 18x10.5 wheels with 285-295 tires. This is the ideal setup if you still drive the car on the street as a dual-purpose car or if you swap wheels from street to track. For 11.0" wheels, and dedicated track use, we had to spec new control arms, tie rods, steering limiters, struts, and alignment. With this combination we can get 305 and 315 slick tires underneath stock bodywork. Our GTMore control arms are made just for this purpose and are not shared with any other application.
This looks like a lot of complexity - and cost - for what is really a hobby for most of us. But look closely at the kit and it's not any more components than what most hardcore track customers will buy anyway -
+ coil overs and springs - everybody jumps to coil overs but they are usually a compromise for some street comfort. MCS are the best coil overs on the market and you should be running these at this level.
+ camber plates - of course you should have camber plates for track use!
+ tubular control arms - at this level you should have some added adjustability in the suspension for a better track alignment
+ spherical bearings - with grippier rubber the bushings and bearings need to be upgraded to match the extra grip
+ tie rods - most track builds will not change tie rods but we needed to on this project. If everything else is tubular and spherical, these should be as well.
+ steering limiters - most track cars will have these (or should), especially if you have brake cooling hoses.
When you weigh the pros and benefits you will likely be buying all of the above anyway. If you're starting a fresh F8X build you likely won't be spending much more to get the correct wheel and suspension package.
GTMore Suspension Package Contents:
MCS 2-way, 3-way, or 4-way dampers.
BimmerWorld Camber & Caster Plates.
Hyperco race spring set.
GTMore-exclusive SPL tubular arms.
Spring and damper hardware.
To view more information on the GTMore suspension, including pricing, click here.
M4 Sway Bar Upgrade
Sway bars are part of any serious track upgrade. True to form the GTMore project included a set of Hotchkis front and rear sway bars to fine tune the balance. And like many other GTMore upgrades there was a hitch - the rear sway bar did not fit will when used with a rear coil over damper like our MCS. This would not be an issue for most any other F87/F80/F82 build since the most common rear setup is a divorced damper and spring. But with the highly specialized focus of GTMore we could have no compromises. We worked with Hotchkis to make small changes to their rear bar design to better accommodate the rear coil over springs and perches, as well as the wider rear wheels and tires.
M4 18x11 Wheels
18x11 wheel options are limited unless you have custom wheels made. Our desired front offset is -2 to -7 but because of the wide difference in offsets between the front and rear, we have to compromise on offset and use a very large spacer on the front. Below you will find details on the wheels we have researched.
18x11 ET?? BimmerWorld TA16. Specs To Be Announced soon. This will be our lightweight forged wheel with years of race-proven performance and strength. We have come up with a new offset for the GTMore project and intend to release this spec in Spring, 2022.
18x11 ET30 with 32mm Spacer M4 GT4. As the factory GT4 setup these are a direct fit.
18x11 ET25 with 30mm Spacer / 18x11 ET44. If you have 11.0 ET44 on the rear and simply want to add two front 11.0" wheels you can use the ET25 that is available from multiple places. You still need a front 30mm spacer to reach the ideal offset. The rear fits without spacers. The downside to this setup is that you cannot rotate wheels/tires. But you do get 305-315 tires at all four corners.
18x11 ET44 Square Set. We don't believe this is an option worth pursuing. To get to the desired offset you would need a 48-51mm spacer (essentially 2 inches). We're not aware of anyone that makes a spacer in that size for BMW and no one that makes wheel studs long enough to work with it. It's too bad there is no solution here as there are a lot of these wheels on the market. They still make for a good rear wheel in a staggered set but it's not a front fitment we are going to pursue.
18x11 ET25 Square Set. Since the ET25 will work in the front, why not use it in the rear? The offset is too low.... BMW spec'd a high offset in the rear, making it much more difficult to run the same offset in the front and rear. The low offset will make the tire poke outside the fender.
18x11 ET34-37 Square Set. There are several wheels on the market that have these specs. These should work with the appropriate spacer. Stay tuned for more details.
Remember that wheel spacers need to have longer wheel studs.
M4 Racing Steering Wheel Upgrade - KMP Corsa Wheel
Speed comes from within.
It feels like we have just as many hours from the seat of a race car as we do in our everyday street cars. That's why a racing steering wheel was the first upgrade we did on GTMore. Replacing the "school bus" sized factory wheel for this special OMP Corsa wheel is a big improvement not just in feel but in setting the tone for this build.
And this is not just any race wheel because you can't bolt on a universal wheel to an F8X car and expect everything to work. The electronics are much too sophisticated for that. The engineers and craftsmen at KMP Drivetrain in The Netherlands have reverse-engineered the factory electronics, clock spring, and hub to provide a bolt-on race wheel for F8X as well as other modern BMWs. Some minor wiring may be required but the beauty of this wheel is that it retains the critical functions of the factory wheel and is customizable for others as well. We had ours built to retain the M1 and M2 mode buttons, horn, and traction control settings. KMP supplies the correct plugs and wiring to make it all work.
Normally we would not recommend removing your air bag without first having proper 4 or 6-point harnesses, a proper seat, and a rollbar. But all of those things are just around the corner. Adding this wheel first puts the focus on the task at hand - speed. Because racecar.
M4 Racing Seats & Harnesses
Not only are we strong believes in track safety, many clubs and organizations are requiring better safety upgrades. We have our own minimum standards for our track cars and we're happy to see groups around the country taking a closer look at safety.
For the GTMore we're still interested in keeping this street-able. Maybe trailering a car to the track is the ultimate goal but for this project we still want to have a car to drive on the road and then bring to the track. The GTMore got a set of OMP racing seats, Lifeline 6-point harnesses, and a JP Marketing 4-point bolt-in roll bar. At the end of the day we dropped over 30lbs compared to the stock power seats.
BODY & AERO
+ BimmerWorld GTMore Front Splitter
+ BimmerWorld Swan Neck Rear Wing
+ Alcon 380mm front & 355mm rear racing brake kits
+ Performance Friction pads
+ Red Line brake fluid
+ BimmerWorld "Oil Overfill Kit"
+ Epic Motorsports Stage 1 Street flash
+ KMP rear differential bracket and mounts
+ BimmerWorld GTMore front tubular control arms
+ BimmerWorld GTMore front camber plates
+ BimmerWorld-MCS GTMore dampers
+ Hyperco springs
+ SPL rear tubular control arms
+ BimmerWorld-Hotchkis front/rear sway bars
+ BimmerWorld TA16 18x11 square wheel set
+ BimmerWorld TA5R 18x11 square wheel set
+ BimmerWorld or GT4 front wheel spacers
SAFETY & INTERIOR
+ KMP Corsa steering wheel
+ OMP HTE-R racing seats
+ BimmerWorld seat floor mounts
+ Lifeline Copse 6-poiint racing harnesses
M4 Takes on the Sandhills Open Road Challenge (2021)
All of this work ain't for nothing. So when OPTIMA Batteries told us about the Sandhills Open Road Challenge we knew the GTMore was going. It would also give us an opportunity to test out some new brakes, tires, and suspension upgrades we've been hard at work on.
What is the Sandhills Open Road Challenge? Just one of the best-kept secrets in amateur motorsports in the country. In central Nebraska every August you will find the Heartland's version of a tarmac TSD rally (Time Speed Distance). It's a "run-what-you-brung" event put on by the residents of Custer County, Nebraska. They close the local roads for a week and let racers run loose on them. All earnings from the event go to the local community.
Think Nebraska is flat land with corn in every direction? You couldn't be more wrong. We encountered long straight-aways topping 160mph that ran in-between twisting and snaking tarmac roads. The road surface is quite bumpy which gave us plenty of opportunities to tune our excellent MCS dampers. There are a variety of events throughout the week, mostly of the TSD format - complete the course from A-to-B in a prescribed amount of time, averaging the specific speed for your class. Closest to the target time/speed for the given distance is the winner.
We'll add more content here soon but for now check out some of the videos below.
26.6-Mile South Leg TSD Stage
Standing Mile ShootOut
M4 in Grassroots Ultimate Track Car Challenge (2021)
HyperFEST is the annual festival of all things automotive held at Virginia International Raceway (VIR). Sponsored by Grassroots Motorsport magazine and supported by BimmerWorld, we had multiple cars on and off the track this year. We used the opportunity to test out some new aero and suspension upgrades for the GTMore. Our new swan-neck rear wing made its first track appearance. Consisting of a 13.25" core and swan-neck uprights we had some very favorable feedback from Devin Jones, a driver of one of our M4 GT4s. We also got a lot of compliments from the paddock and other participants. We also tested this package with a M4 GT4 front splitter to baseline the aero balance. We found that the swan-neck rear wing made much more downforce than the GT4 part so we'll be designing a new front splitter to match.
M4 at OPTIMA's Ultimate Street Car Challenge at SEMA (2021)
BimmerWorld brought two cars to SEMA for OPTIMA's Ultimate Street Car Challenge event, held just outside of the Las Vegas Convention Center. While not officially competing the GTMore spent plenty of time on track, giving demo rides and drift exhibitions. Until we inadvertently shredded a brake line while shredding a tire. Still, we got some additional time behind wheel with a new front splitter design. Fresh from the mold and 3D printer we put this prototype splitter through its paces, albeit in a autocross-style parking lot course.
M4 Arrival Gallery:
M4 Aero Upgrade Gallery:
M4 CCB Race Pads Gallery:
M4 Seats & Harnesses Gallery:
GTMore Parts Catalog:
Body & Aero
Intake & Exhaust
Safety & Interior
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