Fuel cell design - running lines from trunk to engine bay

[Mick]

Thanks for the info.

Did you run both pumps from the factory wiring with the 7.5 amp fuse? I'm running 2 pumps and considering adding a solid state relay to power them. The easiest way to do would be to use the old fuel pump power to trigger the relay, but it's silly to have a relay trigger another relay, so I'll probably chase down the input to the main fuel relay and make a home run from there, if it's easy enough to get to.

I have the same concern about the lines coming through the trunk floor, I haven't taken a good look to see if there is a good place to do it.

What do you guys do for filling? It seems like filling using a funnel in the trunk could be a pain, and make a difficult to clean mess if you over-fill, which I'm apt to do. I'm contemplating running a remote fill to where the OEM filler cap was. It looks like I could easily fab a backer plate and tuck the new cap neatly behind the fill door.

[jimmy p.]

I use the funnel in the trunk method, I drilled a port into my fill plate that allows me to use a dipstick to check level.
I do a pump out after each qual / race so I always know what I am starting with.
Yes when I do track days or instruct and I just want to fill it up, yep I spill some gas, my funnel actually has a pile of gas wiping up rags that live in it just for that reason.
I did not do a remote fill, I was going to and I stopped myself after the Dale Earnhart Jr crash at (i think) Sonoma. He backed his Corvette into a tire barrier or wall pretty hard and you can see the body tore away the remote fill line from the cell and thats where the fire ignited. It was a huge fire.

My thought was right now filling into the actual fill plate with a funnel my cell is as intact a vessel as I can make it.
If i run a remote fill line to the 1/4 panel or the rear license plate area like the factory cars did if I had a significant rear impact "it could" sever that remote fill line.
So I stopped myself from doing that. I was 100% going to do it until I saw that crash / fire. I saw it live on TV and I could see exactly what happened as it happened.
Made me re-think the remote fill line.

[1990m3]

Mick - I use the funnel method for now too but only because I haven’t put a fitting for filling by the license plate. It’s also the only reason I haven’t swapped to a pin on trunk yet either, my trunk is on factory hinges and makes fill ups easy. I’ve overfilled before but it’s not the end of the world for me.

I used the factory wiring for the two fuel pumps and just relocated it. I have them on the same fuse but I don’t recall the amperage. I converted my entire car to custom wiring and I use a pre made to order mil spec fused relay box / switch panel setup from racespec. Frankly, it’s awesome and simplified the entire car, especially when I went to a Link ecu and AiM dash, I’m willing to bet there are few m3’s with as little wiring as mine

I brought my lines through to the backseat and then did bulkhead fittings into the factory fuel pump cover and under the car. The surge tank is right below the cover where the old tank used to be and the lines run over the driveshaft and then up the passenger side. I figured if I wanted to change the setup I could just get a new fuel pump cover for the backseat and it looked good again. I’ll find the pics and post some later.

[jimmy p.]

I think I told you I also rewired my car a while ago. Mine is all home runs and breakers (or a breaker and a relay). Its basically wired identical to my Gruppe A car.
Like Dave said, there is not much wire in there at all.
I have my one fuel pump on a relay which is fed by a breaker, the control side is triggered by my ECU

[jimmy p.]

If you have not seen it, this was what stopped me from making a remote fill setup to the rear of the car:

https://www.youtube.com/watch?v=FGR0KWLs51c

I had not seen this bit of footage & interview, but the rep confirmed it was the remote fill that tore away.

[1990m3]

Jimmy -- shouldn't a one way valve and a soft connection between the cell and the bodywork be acceptable? It's so common - although I know pros use dry break fittings for fuel, amateurs probably won't drop that kind of money on a setup.

[Mick]

Man that's scary, I'm convinced not to do it. Thanks for the heads up.

[jimmy p.]

Jimmy -- shouldn't a one way valve and a soft connection between the cell and the bodywork be acceptable? It's so common - although I know pros use dry break fittings for fuel, amateurs probably won't drop that kind of money on a setup.

I think it was just residual fuel in the neck.
A dry break wouldnt prevent that (and I'm 99% sure those factory Vettes had dry breaks).
All the cells have a one way flapper in the fill plate, I'm sure you have had yours apart, you see its just a rubber flap with a stainless steel spring that if the car goes inverted the weight of the fuel holds it closed enough that the fuel doesnt pour out, but the inertia of that kind of crash you can see the fuel spray out. I think it was even mentioned in the segment.
My Gruppe A car has that same remote setup you see in all the Gruppe A car pictures (no dry break, but it came in the spares box), that exact same thing would (could?) happen if I backed that car hard into a barrier.
Since I don't do enduros with my club racer, I feel like Im fine using the funnel in the trunk method.
The Gruppe A car will stay the way it is, because history demands it LOL.

[1990m3]

I think it was just residual fuel in the neck.
A dry break wouldnt prevent that (and I'm 99% sure those factory Vettes had dry breaks).
All the cells have a one way flapper in the fill plate, I'm sure you have had yours apart, you see its just a rubber flap with a stainless steel spring that if the car goes inverted the weight of the fuel holds it closed enough that the fuel doesnt pour out, but the inertia of that kind of crash you can see the fuel spray out. I think it was even mentioned in the segment.
My Gruppe A car has that same remote setup you see in all the Gruppe A car pictures (no dry break, but it came in the spares box), that exact same thing would (could?) happen if I backed that car hard into a barrier.
Since I don't do enduros with my club racer, I feel like Im fine using the funnel in the trunk method.
The Gruppe A car will stay the way it is, because history demands it LOL.

I agree and even at that, I did do a 60 minute enduro and had enough fuel to make it through. It was a short track (not on throttle as much) so that likely helped too. I understand the fuel in the fill line part but to me the whole thing is just very situational. With that said I have no plans to change my setup anytime soon. It's one of the rare things on my car I'm content with as is, it's not broke so I'm not fixing it!

[jimmy p.]

I agree and even at that, I did do a 60 minute enduro and had enough fuel to make it through. It was a short track (not on throttle as much) so that likely helped too. I understand the fuel in the fill line part but to me the whole thing is just very situational. With that said I have no plans to change my setup anytime soon. It's one of the rare things on my car I'm content with as is, it's not broke so I'm not fixing it!

I do agree 100%. Its very situational.
My Gruppe A car made it through a 6 season professional career and then the subsequent remaining years doing hillclimbs and then my ownership without burning to the ground, as do so many race cars. but I figured, hey why take the chance since I don't need it.
I am also in that same line of thinking on it, if its not broke don't fix it (and its so very rare in my car life to actually have the clarity to NOT mess with things that are working just fine).

[loupi]

Hi guys . Watch this video with poor Renaud Verreydt and his M3 GroupeA: https://youtu.be/YRZNJqkaVQM

[Mick]

That's a brutal hit, glad they got out before it ignited.

[Ironhead]

Those rally events are so dangerous, racing flat-out on unfamiliar roads, unpredictable surfaces, and absolutely unyielding obstacles (like a concrete power pole) all around.

I admit freely, I wouldn't have the balls to participate.

[Mick]

I finally got this done.





Pumps are run directly from the battery using a solid state relay triggered from Motronic pin 20.

I put a dry break in on the return side and a quick connector on the relay ground. That way I can easily drain the system.



The vent is looped over the trunk hinge and through the fender to where the old filler neck was.



I went through the trunk floor with bulkhead connectors and used these clamps from McMaster, which can accommodate both lines.

https://www.mcmaster.com/3225T245/

The pulse dampener has an NPT port so it was a convenient place to mount the gauge sensor.





When I first installed the system I was using a Ross Machine FPR that uses a VW style insert, but for some reason with the 3 bar VW FPR I was getting 3.8 bar. I tried 2 different inserts with the same result so I gave up on it. It was quicker, cheaper, and easier to switch to an adjustable FPR and dial in 3 bar than to schedule a dyno and retune.



Out with the old.



The car gained 1 lb after install. Even though the weight has been moved higher and behind the rear axle I think it'll still be a net benefit because I should be able to run a lot less fuel. With the stock tank I had to always keep the tank above 1/2.

Thanks to everyone for the help in planning this.

[jimmy p.]

Looks great Mick. Great outcome.
Is Radium the brand of the fuel cell?
Looks like a very nice assembly.

I'd love to hear more about the cell and pumps you selected.

The 1lb delta will be repaid a thousand times over in the new utter simplicity of your fuel system over a street tank system, and in your safety should you ever have a serious incident.

I also added a dry break tube into the cell fill plate just for pump outs.
I re-used my old stock fuel pump with alligator clip leads on it to the battery and made a little bracket to hold it on the car while pumping out the cell.

Thanks
Jimmy