Fuel cell in trunk
 

So I have this used 15-gallon Sport ATI fuel cell that I picked up last year at a good price. Right now it is sitting on my garage shelf, calling me, beckoning me...
http://www.atlinc.com/pdfs/Racing/AT...log-Page12.pdf

I have a new LSx swap chassis I am building (almost finished) for NASA TT2/ST2 and am allowed by the rules to add a fuel cell pretty much anywhere I want. Originally I was going to add it to the passenger floor board to get some weight on the right side of the car a-la EP Miatas. However the more I think about it, the more I really do not want to give up the passenger seat spot since I enjoy giving rides to friends and HPDE students. Plus I am going to add some ballast to the car (to be class legal) so I'll be placing that on the passenger floorboard, which will help move some weight to the right side anyway. It is going to be a lot more ballast than the weight of the tank.

I am seriously considering removal of the stock tank, and installation of the fuel cell in the spare tire location. Per the rules, I can cut out the spare tire section (1999 chassis) and put the fuel cell there. The fuel cell is a little deeper than the spare tire well but there is no exhaust at all under the trunk so I do not have to worry about clearance for that. This is all DIY so most of my cost is already sunk (the fuel cell).

One significant benefit, beyond the usual fuel cell benefits, is that I'll move a lot of weight aft, which I could use according to the corner weight scales. I am not really doing this for safety, since empirically it has been shown that the stock Miata tank is already pretty safe; my class does not require a fuel cell.

I would use the stock filler neck and cap, and route a hose down to the inlet of the fuel cell.

So, race fabricator crew, any significant unintended consequences I have overlooked? Cons?

Discuss...

I have been seeing fuel cell installs alot more lately. I think it was Kieth's V8 that they installed a fuel cell in the stock location, but could be removed from inside the car. The rear sub frame doesn't allow to install to lower than the stock tank. With the V8 cars they are normally about 54/46 and I would think if you can now mount it lower in the trunk, it would be a better location to disperse the weight of the swap.

I dont like it in the trunk for 2 reasons. Number 1 and more important is crash safety, I want as much structure of the car surrounding the fuel cell/tank as possible. Number B is polar moment of inertia. You want to focus all your mass to the center of the car or at least between the axles. While putting something behind the axles can help move the weight distribution back more it hurts your polar moment of inertial so it makes the car change direction slower. In most cases this is a bad thing.

Agreed on the crash safety. It's not as protected in the back. Not that I am one to temp fate, but it is a fuel cell...

I considered the yaw moment of inertia but it is hard to say whether that is a net worse situation with the lower and farther aft CG. Maybe it is, maybe not. This might be a bigger deal in autocross? FWIW I know of least one high horsepower car that is placing their ballast in the trunk, and that car is the current record holder of all the track lap records for NASA TT3 in this region.

I would never place 100+lbs of ballast behind the rear axle in the name of better weight distribution. I do place 90lbs of ballast in the PTE car, but it's directly ahead of the rear bulkhead. 60 in the car, 30 under it.

Like his fuel cell

https://www.miataturbo.net/attachmen...ine=1390797222

Great picture

Too bad those Turner Motorsports guys are a bunch of morons or I'd consider this a good example. It's not like they ever win anything.

Different chassis, different goals. E92 M3s have 16 gallon tanks from the factory, and there's nowhere else to put a larger one. John, you're doing TT and 25-minute ST races, and even with a 325whp LS, the 13gal 1.8 tank will do that without any issue. I'm struggling pretty hard to see why you want to do a fuel cell.

IMHO.....x2 what Leafy said and TMS guys just won at Daytona so they must be doing something right.

The factory location is really great in general. Are you able to place the cell there? I don't know if your rules allow it (based on cutting that area apart to make it fit) but that's what I'd look into.

If you install the fuel cell in the rear, your rear "ballast" is not fixed. As you go through the race, your F/R distribution will become more and more front-heavy.

The fuel cells in our Grand-Am cars are installed similar to the Turner car showed above. Way further back than you would think "makes sense". About as far back as you could be and stay legal and safe.

Our cars are Fael Wheel Drive tho...

Something else to consider about fuel cells is they're typically not baffled very well, so you have to be creative with your fuel pickup to ensure you do not starve under high-g cornering and/or braking. I've seen it done different ways, from Grand Am cars with 4 pumps per tank to fuel swirl pots with secondary pumps to creative installation of sumps. I assume your ATL tank has a bladder, so you're probably looking at a multiple pump solution of some kind.

Because I can't leave well enough alone... Mod fever...

Yep I don't need the extra capacity. I burn about 2-3 gallons of fuel per outing depending on the session, and I have no plans for serious endurance racing anytime soon.

Actually another downside is that it takes up some space I want to use for something else l have in mind for later on. An upside is that it would make for easier installation of something else I have in mind for later on. The latter however is a borderline psychotic desire to add more power, so I don't expect to be doing it anytime soon.

Yep on the surge tank. It would need one. That means another pump (low pressure), a high pressure external pump, a surge tank, and more plumbing. All that will add up quickly if done properly. With the surge tank I would only need one of the two duckfoot pickups.

I would not want to put it in the stock location. In that case I'll just stay with the stock tank. It's not that I HAVE to add the fuel cell, it is that I already have it in hand and am thinking about ways I might use it that would improve the car, other than placing it on the passenger floorboard.

Thanks for the input all. Still thinking about it.

I don't think putting it anywhere but the passenger floorboard would improve the car. Putting it in the stock tank location will raise the CG slightly, but the added capacity might be worth it. Putting it behind the current tank will mess with the handling of the car.

I'm all for mod fever, but don't make the car worse ;)

If you put it in the back, you will sacrifice handling at one fuel extreme. Either corner weigh & align with a full tank & get a rear end that steps out at then end of a session -or- align it empty and have a pig at the start of the race.

I had a terrible time trying to keep the stock tank from fuel starvation in a MSM PTB car - cut the tank apart & added baffles, external swirl pots, etc Pretty much had to keep 4 gallons in it at the end of a race (which was extra weight we didnt need).

Fuel sock was wrong or you had the fuel pump installed wrong (or a larger aftermarket pump that couldn't be installed right). Stock location pumps with stock fuel socks do not starve in Miatas. Even the Walbro fuel sock that sits straight off the pump (vs. the stock sock that drops down) will leave over a gallon in the tank when starvation sets in. Stock pumps with stock socks leave ounces in the tank.

This.


Always use the OEM sock and make sure it is oriented like stock, not higher or lower.

Don't know anything about RR rules as I've only ever autocrossed, but here's an example that is within the wheel base and lowers the CG point. Holds 4.5 gallons.

+1 on the fuel pump sock. BTDT.

Dunno what the cause was (and moot at this point). It had an uprated pump & we even switched back to a drop in module (OEM mazda with sock & all) with no change. With the returnless system one air bubble took 1/4 lap to clear.

I'm sure the stock tank / pump can run with ounces in it but my guy with 225 A6's on would get starvation under long LH sweeping corners.

Anyway, sorry for the highjack..