11 replies to this topic

[hatchssv8]

Researched for answer in the threads but could not find info/answers I was looking for, so below is what I am planning for-

 

Its a LX, 5 litre EFI from a VS commodore, 400hp max, street car

 

Originally i was going to use a 120ltr BD drop tank with a VZ in tank mra  (tall unit)

This has now changed to using a 90 ltr BD drop tank which now means I will use the VE MRA (Short unit)

The VE MRA has one only outlet, internal reg and pot.

The tank has 3 breathers (1/4 or 5/16) located high at frt of tank.

Tank also has original fuel pick up boss to which i will fit the pick up/level sender unit. This will be my fuel return.

 

My intention is to use standard LX fuel line from MRA outlet to inline filter to VS fuel rail.

Exit fuel rail via the standard reg (vacuum type) and return via same size fuel line to the original fuel pick up barb on the tank.

 

The three breathers on the tank will be plumbed to the  original vapour separator (bottom barbs), the output of the separator (top barb) will go to the charcoal canister. Then from canister to engine manifold/TB.

 

The fuel tank cap will be VZ type. So will the fill tube. I will also plumb the filler breather to a suitable (same size barb as on filler tube)  fitting on top of tank. This fitting should be a anti rollover type (allows air out of tank when upright and seals passage if inverted)

 

Have I missed something? Is there anything that will not work as intended? I want to cover all bases now before the tank is made should i require any mods.

Let me know what you gurus think.

 

Thanks in advance, Hatch

[yel327]

Can you use an internally regulated MRA with a VN-VS fuel system?
I’m using a Holley Sniper Quadrajet system with a VY MRA in the HK, but it is designed to be able to be returnless like a VY. If the VS system will work with it you don’t use a return line from the engine, you use a VY filter in front of the tank with a return to the MRA. The original filter has 3 lines off it, one from the pump, one to your original fuel line to the engine and one back to the return port on the MRA.
I just recently bought all the original filter, the bracket that holds it, the zip tie thing that holds the filter and the original lines, I have all part numbers if you like. The 3rd port on the MRA is a breather.

[hatchssv8]

Cant see why not, in terms of pressue I am regulating twice. fixed from the tank and variable at the fuel rails.

I don't think there is any issue with that part.

I am more concerned if I have the tank/lines/breathers in a working configuration.

[yel327]

Going from memory the MRA regulates to 4bar and is designed to be operated dead head. I don’t think you regulate it again and use a return line? If you use the regulator on the engine and a return line you are better off with a high pressure (unregulated) MRA. That is how I understand it anyway, I’m no expert though, just looked into it enough to make it work on my HK.

[ls2lxhatch]

If you configure the VE fuel pump using the LX pickup as a return line then the fuel pump will empty its pot into the tank making fuel surge more likely. 

 

If you want to run a return line system, then it would be better if you configure the return line to return fuel to the VE fuel pump pot.

 

Another problem with return line systems is the build-up of heat in the fuel tank.

 

The beather setup sounds like it will work.

[hatchssv8]

ls2lxhatch,

great feedback

yep, plumb the returning fuel into swirl pot.

 

regarding heat build up- is it a trade off between having cooler fuel at the injector rails?

If I don't return the fuel and block the rail, how do I drop fuel pressure in high vacuum state? wouldn't it make the fueling difficult?

[yel327]

That is what I meant by the very first question I asked, ie will the VS ECU and EFI setup work with an MRA regulated fuel supply? I thought it needed a high pressure supply with vacuum modulated rail pressure. Someone here will know the answer hopefully.

[76lxhatch]

The original Holden EFI setup requires constant fuel pressure so the regulator is at the fuel rail with a return line. You'd need to change something to allow it to run return-less as the pressure at the rails varies with that config, not sure if its possible without hardware changes or not, wouldn't be straight-forward.

 

However if the regulator at the pump is 4 bar it should be fine to leave in place as suggested since the regulator at the fuel rail is only 3 bar for the original system.

 

edit: when I say constant fuel pressure I mean across the injectors regardless of engine vacuum, I suppose technically when the supply is regulated that's actually more constant

Edited by 76lxhatch, 06 May 2020 - 10:34 PM.

[hatchssv8]

yel327, will the VS ECU and EFI setup work with an MRA regulated fuel supply? yes 

 

76lxhatch, no need for software or hardware changes as I have now been advised.

 

Now I just need to package all of this back into the car with the add-ons and tick Fuel system off the ToDo list

[yel327]

Good to know. You’ll have to update how it all goes.

[76lxhatch]

yel327, will the VS ECU and EFI setup work with an MRA regulated fuel supply? yes 

 

76lxhatch, no need for software or hardware changes as I have now been advised.

Only if you use the return regulator in addition to the regulated supply as per your first post though?
 

[hatchssv8]

spot on