In the constant quest to keep a terrible beater of a vehicle from falling apart during the undue stress of endless hours of endurance racing, the spectre of speed always looms. Sure, the name of the game is reliability when you're trying to rack up laps in a field of 150 to 180 cars. Simply finishing the race without any major failures, accidents, or penalties will likely lead to a respectable result. But if you want to contend for the lead, you have to do all of those things, plus be really quite fast both on and off the track. For the Black Iron Racing Brougham d'Bavaria we handled the on-track speed with our 5.3L V8 swap, but off-track speed - i.e. pit stop time - was pretty terrible during the first race. The stock E36 fuel tank with its restrictive filler neck (which made filling an exercise in gasoline spill remediation) meant we had to rethink our entire fueling situation for the 2nd effort. Enter ATL Racing Fuel Cells and one of their high-tech but affordable solutions to let us fill quicker and stay on track longer.
We called up the good folks at ATL (or Aero Tec Laboratories, if you're not into the whole brevity thing) in Ramsey, New Jersey after searching through their extensive catalog, and learned about the Super Cell 100 Series, which is intended to serve the needs of most budget / crapcan endurance racing teams. This cell consists of a thick flexible bladder encased in a lightweight but sturdy aluminum box, and we ordered the largest one that they offered (22 gallons) that would comply with the 24 Hours of LeMons rules (24 gallons max). Step 1, other than cutting a hole in the proverbial box, was removing the stock plastic fuel tank from under the rear seat area of the E36. That left us with the big void seen above.
Being engineers, we figured ideally that the new fuel cell should sit as low as possible, and as close to the center of the car as it could, to minimize impact on the vehicle's roll couple and polar moment of inertia (glayven). So I drew up a quick schematic to explain our proposal to LeMons Tech Tyrant John Pagel. Please excuse the drawing above, as I didn't have time to make it to scale, or to paint it. Anyway, the original idea was to cut away part of the seat pan and sink the new cell down as low as possible, so its lowermost protuberance was about the same height as the bottom of the original gas tank.
That's all well and good, but it turns out that a 22 gallon fuel cell is quite large...actually. Once we had the shiny new piece of hardware in our eager hand-holes, we found that there simply wasn't enough space to get the cell to fit on the passenger side where we envisioned it. The vaguely rectangular space defined by the driveshaft tunnel at left, roll cage main hoop in front, passenger side rocker panel to the right, and rear suspension subframe at rear simply wouldn't fit the big honkus of a box. Plan B was quickly devised which involved centering the cell in the car if we couldn't get it as low as we wanted. Out came the angle grinders and reciprocating saws, and a large ski pass-thru was cut into the rear seatback firewall of our E36 sedan.
The new great idea was to put most of the weight over the rear axle, within reason. With the new cell centered side to side, and sitting on the trunk floor between the shock towers, the only degree of freedom remaining was longitudinal. So we compromised and chose a position that protruded minimally into the cabin, but seemed to center most of the weight over the rear wheels. This ended up being at least six inches further back than shown above.
Following ATL's own recommendations in their Installation Procedures, BIR Fabricator-in-Chief Nathan started work on building a steel cage to secure the fuel cell to the BMW chassis. Square tubing and angle iron came together quickly, using our resident MIG machine. The front uprights were welded to some steel tabs acting as brackets, which we bolted into the OE seatbelt buckle mounting holes. These are weld-nuts designed by BMW to hold the weight of occupants in a crash, so we figured that this would be a safe way to secure our big box of gasoline, which should weigh less than 150 lb fully filled.
In a modern car like the E36, the stock fuel tank in its stock location is likely the safest option for fire prevention in operation and in a crash. We considered mounting the new fuel cell in the common trunk location, down low, behind the rear suspension. This would place the cell in the spare tire well of our car, between the structural "frame rails" that the bumper mounts to. ATL recommends this type of installation, but we decided against it due to the short rear overhang of our E36. With the cell in the spare tire well, it would be inches from the rear bumper and inside the rear crumple zone. Accidents are a reality in LeMons racing and although this type of fuel cell can survive being crushed without leaking, we decided not to risk it.
|Front of the cell cage/bracket was tacked and bolted in place...|
|...and then the rear, top, and sides.|
Back in the trunk, we cut and welded more square tubing to snugly surround the outer box of the fuel cell and securely mount it to the chassis. Unlike the back seat area this meant making our own nut plates with M8 weld nuts and some steel scrap, then MIG welding them on to the tops of the frame rails, but not before drilling clearance holes for the nuts to nestle into. The whole cage assembly is an extremely tight fit around the cell but is essentially only a clamp since it does not directly fasten to the cell itself.
With mounting worked out, next up was fuel delivery. Our stock saddle shaped E36 tank had provisions for pumps on both sides which is helpful in road racing, as the fuel sloshing from side to side in various corners can cause fuel starvation when the tank is around 1/4 full. Handily, our fuel cell has a nice feature that allows us to get away with only one pump...more on that below. Our LM7 V8 makes around 300 naturally aspirated horsepower, with a standard 3 bar fuel pressure regulator. We knew that stock E36 pumps flow enough for at least 300hp at higher pressures on boosted stock engines, so we chose the best looking one in our stock and hooked it up to the hoses supplied with the cell.
The ATL Super Cell 100 comes complete with a nifty pickup bonded into the rear of the bladder, and surrounded by an internal sump or "surge tank" with plastic trap doors. This is called the ScavenJet and it's quite a cool feature. The white plastic bit above is permanently affixed to the floor of the bladder, but has gaps all around the base to allow fuel to flow in. The nice thing is that this is threaded for easy adaptation to whatever fuel line you need to run. The blue fitting is a standard -6AN adapter that was included with the cell. The trap doors allow fuel into the sump but not back out the other side; these features together help ensure that the pump is never starved for fuel, and your race car can stay out on track until the tank is really bone-dry.
|Image from ATL's Introductory Fuel Cell Design Guide|
These cells probably aren't designed for in-tank fuel pumps, but our improvised setup worked out nicely. By looping the inlet line and going with a standard outlet line supplied with the cell, and some strategic zipties to hold the pump in place, all is snug and scure inside the anti-slosh foam. The pickup snorkus and trapdoored sump need to be oriented at the back of the cell for good fuel supply under acceleration, but that's clearly marked on the outside of the cell so it's difficult to screw up (even for us).
Once the wiring to the pump was complete, attention next turned to the ovoid top cover plate. This piece serves multiple purposes: it seals up the bladder, secures the bladder to the outer box using clamps, and has provisions for all the inlets and outlets needed. The standard cover plate that came with the Super Cell 100 is quite pretty, but it had an integral filler neck that we decided not to use. The cover plate seen above with the secondary smaller circular flange for the removable filler cap assembly was scavenged from an old retired ATL cell that we had acquired years earlier and ended up only using for parts. The top cover plate also incorporates the fuel supply and return fittings, a vent with integral tip-over valve, a dipstick assembly for manually checking fuel level, and a few extra holes for stuff like sending units and wiring looms.
To complete the fuel system installation and get the car running again, we found an el-cheapo AN adapter and hose kit. It came with enough stainless braided hose and various fittings to allow running the supply & return lines over the front edge of the cell, down through two new holes in the rear seat pan, and forward to the stock hard fuel lines. We installed some rubber grommets into the pass-thru holes to minimize any chafing between lines and sheetmetal.
|It runs! Testing the functionality of the cell with newly installed pump and lines.|
So now that we had a nice running V8 with the newly installed cell, we're done...right? Nope - we proceeded to cut more holes in the car. Two things remain. First, since the cell protrudes into the car's cabin, it needs a new firewall to keep it separated from the driver in case of fire. Granted, the LeMons rules allow for a "fully FIA certified installation" to be in the driver's compartment without being completely encased, but it's a bit fuzzy what that constitutes - in our case, the cell itself was certainly certified, but our modified top plates and fuel fittings and pump setup could be called into question. Plus, separating the fuel from the human really is the safe and right thing to do. The second thing left on the list was a remote fill setup. We were inspired by an old quick-fill nozzle that we had sitting around, and decided to use that as a starting point.
The idea was to fill from the rear of the car, putting the cap exactly where the stock 3rd brake light used to live, allowing us to rig up a funnel and pour gasoline with the trunk lid either open or closed. To accomplish this we needed two new flanges: one to bolt to the top of the cover plate in place of the old filler cap flange, and another to mount to the car, aft of the cell, to accept the cap flange and hold it securely.
We started by roughing out some octagons with holes in the center, using the drill press and band saw in our Compton-area workshop.
It's times like this that having a real lathe comes in very handy. The center hole allowed us to chuck up the octagons and turn them into circles in a matter of minutes.
Once that outer diameter was round and roughly the right size, the chuck jaws got flipped around and we turned out the inner diameter. The piece above is the top cover flange for the cell, which will get an aluminum elbow tube welded on, and bolt holes drilled around the outside.
The 2nd flange needed a much larger hole for the ID, to fit our old cap assembly with enough clearance. The cap flange bolts onto the outside and the conical bit of our old quick-fill neck got welded to the inside.
Here's the assembly, bolted into the car, complete with 2" diameter flexy hose that is gasoline rated. The clear braided tubing is our vent line. When you need to dump 22 gallons into a compact box in a matter of minutes, all the air in that box needs some way to escape and allow the fuel to displace it. With a big plastic funnel inserted into the filler neck from behind the car and this big vent tube in place, we can fill as fast as the funnel will flow, without any burping or bubbling or mess.
Here's a closer view of the new elbow flange, bolted into the cover plate. All of the fasteners use special nylon washers where they pass through the flanges, preventing leakage should we overfill past the level of the top of the cell.
At this point the finishing touches were all that was left. A quick bracket welded to the parcel shelf gives that filler cap flange something to bolt to and holds the weight of the remote fill assembly.
The legality box was fabricated by Nathan over the course of a few hours, maybe minutes, of work. It's simply aluminum angle channel at the back with a skin of 3003 sheet riveted over, and foil tape to seal up any small gaps.
The trunk lid seal lip was bent downwards under the filler cap, to act as a drain for any splish-splashin' that may occur while fueling during the race. We can place a drip pan inside the trunk to catch this, with a LeMons-required larger plastic tray kicked under the car to catch anything that makes it through the drain holes we drilled in the old spare tire well.
A lick of paint and some vent routing in the trunk, and we're done. The vent tubing has to go up and come back down below the bottom of the tank to help prevent drainage in a roll-over. That plastic reservoir at right is an old 540i coolant surge tank, re-purposed here as a diff breather catch can. 335 lb-ft of V8 torque tends to overheat old worn-out BMW differentials, as we discovered during our first test day when the stock limited slip puked most of its oil out through the crusty original seals. A breather port plumbed into this catch can helps prevent that from recurring!
Here's the view of the old back seat area with the driver's side rear door open. The aluminum skin fully separates the fuel cell installation from the driver, as well as the cool suit cooler and fire extinguisher it shares space with.
What's this? Another Volvo on Daily Turismo! That's right, this author managed to find a minty green 1975 245 a few months back and thought it might work well to mount the Volvo above the E36 using the beefy wing uprights...here it is being lowered into position... riiight. More on that car at a later date.
Astute readers may have noticed the fresh blue paint job and sparkly clean white vinyl top, as well as new Style 32 wheels. All were added with an eye towards appeasing the LeMons Supreme Court and theming our Brougham more appropriately than our debut race with mismatched body panels and limited Broughambic accessories.
Representing DT are the home-cut vinyl wing decals, with ATL sticker soon to come. Quite fetching if we do say so ourselves!
The LeMons judges smiled on our efforts for the 2nd race, both with reduced penalty laps and a nice writeup on Roadkill. Here's team founder Nathan assuming the position next to Driver (Listener) Dan behind the wheel in the Tech / BS inspection garage at Sonoma Raceway last December.
While our 2nd race with the new car didn't end in victory - that pesky GM power steering pump reared its leaky head again - we did drastically improve our pit stop times and made filling the car both faster and easier. We spilled less fuel and kept more in the car for powering the V8 lump under the hood, extending our driver stints to over 2 hours, depending on traffic and, uhh...aggressiveness of the nut behind the wheel. The fuel cell installation made all of that possible. Thanks to ATL for offering a great budget friendly solution for amateur racers like us!
ATL Fuel Cells
24 Hours of LeMons Rules
Roadkill's Bavarian Brougham Feature
CFlo is Daily Turismo's Technical Editor and co-founder. When he's not trying to keep V8 swapped monsters alive, he's stockpiling Volvos for the afterlife, and the great folkrace in the sky.