Froooog
Froooog is a 2007 Audi RS4 that is built primarily as a hillclimb car but has a stage rally cage that will allow it to compete in gravel trials and stage rallies. You can check our RS4 maintenance page for technical videos.
About the RS4
If you want to know why the B7 RS4 is an iconic car, just watch the Top Gear videos below as well as the Audi v8 history. Between the high revving v8 and the 60:40 quattro setup mated to a 6 speed manual, no word can describe the feel of driving an RS4. You can read more specs on the Audi RS4 wikipedia page.
Froooog in action
We took Froooog for the first time out at the 2024 Okemo hillclimb for testing. The clutch and clutch slave were very tired but the driver also still had a broken left leg limiting the use of the clutch. The full range of RPMs was on display and it was a delight for the ears. We had some surprises on braking due to an uncalibrated steering angle sensor, so we still have to work on msaking the eletronics happy with some of the missing components like the steering wheel or airbag controller module.
The build
Rollcage
The rollcage in Froooog is built to the FIA Article 253 Appendix J specifications to match the current regulations of the rally sanctioning bodies in North America (CARS, NASA and ARA). Froooog has a NASA logbooked cage. The cage has been built by CAS competition located between Montreal and Quebec city in Canada.
The design document for the cage is in the Google doc below:
The car prep work for the removal of the interior and the weighing of the car is documented in this video::
Here are a few pictures after the rolkcage build. You can see the main structure of the cage (253-3 with 2 diagonals in the main hoop 253-7) gusseted to the A and B pillars. Double V roof bar configuration (253-14 / 253-22), X door bars (253-9) with an optional sill bar, 253-15 windscreen pillar reinforcement, 253-17/253-18 optional rear reinforcements and an integration with the stock dash bar. The sunroof is also patched with a cutout metal piece. New seatbelt mounting points for the lap belts are welded on the chassis.
Roof patch
The regulations mandate a steel roof to patch the sunroof opening. CAS competition had a laser cut piece of metal that we painted and then covered weith a carbon fiber looking vinyl wrap on the outside. The whole panel is secured with pop rivets and then sealed with all weather calk.
Dashboard
The stock dashboard was retained with all the light controls, most of the HVAC piping and the original aluminum trim that provides extra rigidity. Note that the glove box could not fit with the bars of the cage. The center console molding was reinstalled to provide heat insulation from the transmission tunnel. The stock gauge cluster is required as part of the security system and the car will not start without it.
The Sparco IS-140 intercom has been secured on top of the HVAC controls and the Cartek GT kill switch (see install video in the next section) is secured to the plastic fill piece next to the coin holder.
Kill switch
The Cartek GT kill switch installation has been documented in this video:
Seats and Harnesses
We are using Bimarco Phantom seats with our embroidered Frog Racing logo. These seats are the new version of the Bimarco Grip we used in our other rally car. The seats are attached to Sparco (on the driver side) and OMP (on the passenger side) seat brackets that are secured to Planted seat mounts that use the factory mounting points for the seats.
New anchoring points for the belts were added for the lap belts and for the crotch belts. The crotch belts required cutting an opening in the floor reinforcement to insert the backing plate. The lap belts backing plates were welded to the transmission tunnel under the heat shield.
Footrest
An OBP foortest was installed, secured with M10 rivnuts to not expose bolts under the chassis. The lower part of the footrest has been covered with grip tape as the aluminum finish is too slippery especially in wet conditions.
Hood pins
Rally regulations and most road racing sanctioning bodies require the main hood latch to be disabled and hood pins to be installed. Note that hood pins are a wear item and you will have to change the studs over time as they will wear out with the constant opening/closing of the hood at every rally service.
A note that we don't use Aerocatch style hood pins as they do not work in cold weather where ice buildup makes them impossible to open. Also in case of an impact the Aerocatch latch mechanism breaks and makes it impossible to open the hood (but they look nicer for sure!).
The hood pins used in the video below are the generic inexpensive kit found on Amazon at: https://www.amazon.com/gp/product/B08L8TPFYY
Underbody protection
We are currently exploring the offering from OCT composites for the RS4: https://shop.octcomposites.com/car-parts/Audi/rs4-b7
The Ultimate line of products uses 3 different materials:
Kevlar Layers: Known for its outstanding impact resistance, Kevlar helps dissipate energy from rock strikes and gravel impacts, preventing cracks and preserving structural integrity.
Wood Mat Layer: Provides added shock absorption, particularly effective in rough rally environments.
Carbon Fiber Reinforcement: Reinforces the structure without adding excessive weight, particularly in the undertray, which benefits from stiffness and wear resistance.