SLC Fuel tank questions.

Hi All,

The last time I posted in was 2013, been a while... Anyhooo, the scratch built car I'm building has a similar tank design to the SLC (I think).
Please correct me if I am wrong, from looking at photos...

  1. Where the tank is, is not sealed off from the engine bay, but the holes are not bigger than needed for the piping etc.
  2. The cover for the tank seals the passenger compartment from the tank.
  3. There's no drain holes in the floor, in case of leaks.
The questions:

  1. Is there any form of forced ventilation into the tank area?
  2. In case of a fuel leak, where does it go?
My assumption here is whatever is being done with the SLC is gone enough for me, and I don't want to die in a ball of fire.
The link to my blog if interested:


Joel K

Hi Doug,

Nice blog, going to follow along...

I have an SL-C on order and will take a crack at answering your questions. I am not an experienced builder so hopefully others will answer your thread as well.

1.Most people add a panel between the lower engine compartment and fuel tank.
2.yes, I believe it does.
3.Not sure what most people do, there is no mention of a drain in the SL-C Build Manual. If you did have a leak having it drain out the back and have vapors travel into the engine compartment probably not a good thing.

1.No, although that fuel tank area is not totally sealed up on the sides.
2.It sloshes around I guess. I would think if the tank starts to leak you would smell it, but just a guess.
I’ve drilled holes into the panels below my tank so any leaked fuel will have a place to drain.

Is your question about forced ventilation due to concern for trapped vapors or for tank temperature?

If you want forced ventilation you could add some type of scoop to push high pressure air into your compartment or install a brushless fan. Depends on what kind of airflow you plan to have in that area of the car.

Huge props for the progress you’ve made!

Howard Jones

I drilled two small 1/8" diameter holes in the floor of the fuel tank compartment. I placed them at the outboard corners so that cornering would force any fuel out the corners and out of the holes.

Fuel smell = leak. Find and fix leak! Do not assume that fuel smell is "normal" it is not! Here is where I make my speech about onboard fire systems. I'll save you the long version but a very capable 5 pound system can be installed for around $400. Do it!

I covered the rear opening that is between the engine room and the cockpit/fuel compartment. I used 1/8 inch 4140 aluminum, covered it with heat shielding and riveted it on. I did this to add stiffness to the chassis and to isolate any potential engine room fire and engine room heat from the fuel compartment.

The tank itself needs to be vented. This should remove vapors or at least prevent and pressurization. Vent the tank with a roll over valve and run a line all the way to the rear of the car behind the rear tires and low so that any over fill will go onto the ground and away from the hot parts in the engine room. The fuel tank compartment really does not need ventilation because you are going to find and fix fuel/smell/leaks ASAP...…...right?

Fuel lines: IMHO I really like hard lines wherever they can be hard mounted and there isn't a need for flexibility for fuel. (best? stainless pipe with SS fittings. Very good? aluminum pipe and fittings flared and bent with a good tool). SS is hard to work with and you may need to have some of the larger diameter pipe done by a shop that has a power flaring tool but it is a one time thing as it lasts forever. Hard lines will not get old and leak like stainless braided hose does. When you do buy hose, and fittings for that matter, buy name brand. Earls or Aeroquip are good stuff. Russel and other cheap stuff isn't worth the savings when they break as you put them together or leak after a few years (hose).

That's my 2C's, have fun with your build.
Last edited:
I’ve drilled holes into the panels below my tank so any leaked fuel will have a place to drain.
Is your question about forced ventilation due to concern for trapped vapors or for tank temperature?
My question on ventilation was about flammable atmosphere buildup, think boat bilges and the like that can explode if the air is not changed.

The lines will be stainless hard line as much as possible, the tank has a rollover valve on the vent, which'll go down then up the to the back of the car, the return goes to the bottom of the tank so in case it ends up upside down that may limit how much could come out.

One point, I doubt there'd be much of a smell if it did leak, if there was then the sealing between the engine compartment and the passengers would not be that great.

All in all the situation sounds similar to what I am doing, I don't here about SLC's doing a F**i too often so it must be a workable solution.


Joel K

Hopefully I am not hijacking this thread but curious about the term rollover valve. When I look up fuel vent or rollover valves on the various web sites they appear to me to be either vent valves which open when pressure builds up due to increase in fuel vapor pressure, then you have float valves which close when the tank fills up with fuel, then you have a rollover valve which closes in the case the car is inverted.

Are there any valve that do all three actions, float/vent/rollover? What do production cars use?



A fuel cell vent usually has a caged ball that is free to lie in the bottom of its cage, allowing air to enter the tank as its fuel level goes down. If the car gets upside down, the ball falls to the top of its cage, sealing the hole to the air and stopping fuel from leaking out. I don't know where a float valve would be used.

Howard Jones

There are really two types of roll over vent valves. Their use is related to the filling system. The small steel ball bearing inside what looks like a bulk head connection is a smaller sized device that would be used to vent the tank as normal usage draws down the fuel volume. This is the kind we generally use on our cars and they are far less expensive.

The much larger style as described by Neil is generally used when a dump can is used to fill the tank very quickly. In this case is allows a large volume of air to be displaced from the tank as the fuel is dumped in at a very high rate and or a overflow if the tank is overfilled. It will also serve as a vent for normal usage. Think NASCAR.
Also the filler neck that bolts to the tank has a rubber flap valve in it to stop fuel going back up the filler hose, mines a Fuel Safe part if I remember correctly, this will help if the filler hose is torn off and you're upside down and... I'll stop there.