Fuel system plan for RCR40 with bladder tanks

I am in the process of assembling my fuel system and think I have come up with a plan but would like to run it past the collective braintrust on this site.

I have an RCR with bladder tanks, SBF crate motor and Edelbrock EFI. The bladders have a send and return on their aft ends and a large dia filler neck and small dia vent tube fitting on their fwd ends. Just aft of the filler neck is the level sender mount.

For the purposes of this discussion, I will separate the high pressure system from the low pressure bladders to swirl tank.

At the aft end of the left sponson is a tank in the chassis which I intend to use for a swirl tank. I will draw from this tank, through a filter, through the HP pump, through another filter, to the fuel rail and then plumb a separate return from the rail to the swirl tank.

In THEORY, that should take care of the HP side, right?

The LP side is what is giving me questions.

It seems like it'd be pretty straightforward to plumb a pair of lines from each bladder to the swirl tank, one via a filter and a LP pump and the other just a straight return line.

The single vent line at the fwd end should likely be connected with the filler tube (somewhere near the external gas cap, right?) and a rollover vent, correct? Any recommendations for a vent?

I am tempted to run without a selector valve- seems like it's not completely necessary and it'd be an additional opportunity for something to fail. With the unrestricted return lines, cross-filling would be controlled by individually powering the LP pumps. If one is turned off, the return feed will continue to fill the tank based on the volume being pumped from the opposite tank to the swirl tank.

Conversely, feel free to tell me I'm way off course here as well.

One of the major questions I have is will that rollover valve at each side prevent the build up of high or low pressure in the bladders as the gas expands on a hot day or is consumed while being driven.

What other concerns should I have/am I overlooking? What would you do if you were doing it?

Pics can be posted later if you would like them for clarity.

Thanks in advance,

Chris

First problem I see is at some stage you will kit the brakes and the fuel will slosh forward away from the taank pick up point and the LP pump will pump air. (On the Dax from about 1/2 tank stopping at lights will get the facit pumps pumping air)

Without a return from the swirl to the tank (from where the fuel is being drawn) will eventually end up in your swirl tank being full of air

You can connect the 2 tanks together (About 3/4 inch connector pipe) and then have a single return line from the swirl back to the "twin" tanks would work and eliminate change over valves etc. In all honest I wish I had done my car this way having run with changeover valve for 4 years. I think the keep it simple theory is best

Ian

ckouba said:

The LP side...

It seems like it'd be pretty straightforward to plumb a pair of lines from each bladder to the swirl tank, one via a filter and a LP pump and the other just a straight return line.

Click to expand...

Ian,

I know it's a little cryptic and I could have been a little more direct with it but my intent with the above explanation was to have exactly what you describe. I am trying to describe a pair of lines from each sponson bladder to the swirl tank, 4 in total. From each bladder will be one sending line, from the pickup through a filter to a LP pump and dumping into the swirl tank. Returning to each bladder will be the second of the pair of lines- just a piece of tube from a pickup high in the swirl tank returning to the bladder.

I understand and agree about needing to purge the air from the swirl tank for precisely the situation(s) you describe.

I appreciate the comment on tying the two sponsons together but as they are bladders, I don't have much flexibility regarding the addition of holes. I am wondering if someone out there has tried what I am describing and can either confirm it works or can get me pointed down a path which does.

Thanks for thinking about it!

Hi Chris

Yes it sounds simple but I can see the fuel flow on the return will tend to flow towards one tank in preference and could end up overfilling that tank.

To do this you wouuld need solenoid valves in line with the individual LP pump to ensure the circuit is from Left tank to Swirl and back to left tank - same for right tank drae from right - return to right

Solenoid valves can be found in Jag XJ6 cars

Or you're into a pollack tyoe 6 way crossover valve

Ian

Chris

I understand what you are trying to do.
My system is as you explained except I have linked my tanks with a 3/4 tube as Ian mentioned.
I think you will find it will favour one particular tank on the returns from the surge tank to the main,that is why I think you will need the cross over tube as it will self level both tanks regardless of favouring (hard with pre existing bladders).
My way of thinking is if you have to dick around with hose length or any kind of regulation to get the surge tank to spill back to the mains equally it will be inconsistent and not worth having.

Maybe a hose as large as possible from the base of the filler neck to the base of the opposite filler neck may stop one tank over filling maybe an option.

It will only kick in when the tank is near full but that is a possible down side.
Can the bladders be modified is that another option.

For a vent I used nylon line from the tank went up into the filler cavity and fitted a small fuel filter (plastic) to act as a trap if fuel comes up the line,the line then travels back down to the rear of the car to a charcoal canister.
I have the vent hocked up to a small OEM solenoid that turns on with ignition, a hose travels from the solenoid to the air filter.
I never get fuel smells , This is the way OEM do it and it works.

Jim