Thor - MS3X Fuel Pressure

[garrycol]

The Thor RV8 engines have a complex fuel pump, which is 'In Tank' and ECU Controlled - as such there is no fuel return from the fuel rail.

I want to install a MS3X on my Thor using a different fuel tank (has a fuel return) and pump etc. From Megasquirt for V8s I have purchased a suitable 120psi fuel pump and fuel regulator that can reduce the pressure to the required 52psi that the fuel rail and injectors need. The issue I have, is where to place the fuel regulator in the fuel circuit as the fuel rail does not have a fuel return.

The MS documentation has this diagram which has the style of regulator I have with fuel return etc. But as there is no fuel return on the fuel rail it will not work as is.

Fuel Diagram 1 by Garry Collins, on Flickr

I have changed the above diagram so there is a T piece in the fuel line before the fuel rail connected to the regulator. I have removed the fuel return from the end of the fuel rail in the above diagram so the new circuit looks like this.

Fuel Diagram 2 by Garry Collins, on Flickr

With this arrangement I think the regulator should be able to maintain the required 52psi between the 120psi pump and the fuel rail while still allowing the excess fuel to go back to the tank.

Is there anything I have missed?

Thanks

Garry

[SuperV8]

4.7 Fuel Pressure Regulator
The vacuum referenced fuel pressure regulator is essential. It provides constant pressure differential between
fuel at injector nozzle and manifold air pressure [port EFI] or atmospheric pressure [TBI]. This makes the
injected fuel quantity solely a function of the injector open time. Without the vacuum/boost reference connection
you would need an excessively small pulsewidth under cruise/idle and an enlarged pulsewidth under wide open
throttle or boost. Make sure the regulator is connected to a full vacuum source, not ported-vacuum. Check it has
vacuum with the engine idling and the throttle shut.
If you have an adjustable fuel pressure regulator (FPR), set the pressure with the fuel pump running, but the
engine not running - that's your base fuel pressure (it is referenced to atmospheric pressure).
The regulator is typically at the far end of the fuel rail (after the injectors) which recirculates all of the fuel,
keeping it cool and free from air pockets. However, it can be installed anywhere after the fuel pump, but you
may experience fuel heating and air pockets.
If you are using an aftermarket fuel pressure regulator, it is a good idea to also install a pressure gauge, since
most of these are adjustable. For TBI, use a 0-30 psi gauge. For port injection use a 0-60 psi or 0-100 psi
gauge. Most of these gauges will mount directly on a fuel fitting using a 1/8" NPT thread.

Taken from the MS manuel:
Yes would work but may experience fuel heating or air pockets?
Does the GEMS fuel rail not fit the thor maifold?

Tom.

[DaveEFI]

Think the normal way with a single rail system is to control the pump speed via PWM and have a pressure sensor on it to tell MS what it is. But not all types of pump will be happy like this, as fuel flow through them on a return system keeps them from overheating.

[garrycol]

Thanks - I have no idea whether Gems stuff fits as i dont have any of that stuff.

Why would the air pockets develop if the system was bled correctly and why would the fuel get hot?

Cheers

Garry

[SuperV8]

That was just taken from the MS manual.
Thinking out loud:
If the return is before the injectors then the fuel up to the injectors will be in the rail much longer than if the return was after the injectors. Engines are hot places! No I idea if this would actually cause the fuel to heat up but it's a possibility? GEMS fuel rails have a boss for a fuel temp sensor! (I ground this off)
Pumps can introduce air into a fluid (think cavitation) this air would collect at the highest point and form an air pocket.

I think a Gems fuel rail may fit as I think the lower part of the manifold is the same/similar between GEMS and THOR (you need need to verify this) which would be a simple cheap fix.

Tom.

[garrycol]

Ok thanks - I have the standard Thor setup so if was going to get hot it would do so on the OEM vehicles as there is no return on them.

Everything is stock on the engine - it is only things away from the engine like the fuel pump and ECU that are different.

Cheers

garry

[DaveEFI]

Thor and Gems have very different inlet manifold castings, and I don't think the fuel rails can be swapped easily. (But not tried it)

The Thor fuel rails appear to be insulated.

[SuperV8]

Thor and Gems have very different inlet manifold castings, and I don't think the fuel rails can be swapped easily. (But not tried it)

Yes, the upper manifold are very different, but the lower part of the inlet manifolds look similar.

[stevieturbo]

The pump is not a 120psi pump....the system will only make the pressure the regulator is set to up to a possible maximum the pump may be able to create.

And there is absolutely nothing wrong with the second diagram you propose.

Dead end rails are fairly common. I would still try and keep the reg local to the rails though, although again most modern cars these days have the reg built into the tank with a dead end line to the rails.

[garrycol]

Hi all and thanks for your responses.

I have two complete sets of Thor induction bits and I have a Thor engine. I do not have any GEMS stuff and it is almost impossible to get here and if you get it you have to buy everything at considerable expense not just the bits you need.

Attached is a pic of the Thor fuel rail - it is not insulated - it is a large box section with the fuel pipe going in about an inch. So I take it that heating of the fuel is not an issue. Likewise the bleed screw is only on the left bank so air in the system is not an issue - I assume it is a bit like my TDV6 diesel the air just goes through the injectors and while there is a bleed screw on one back it is not needed.

20171110_105222 by Garry Collins, on Flickr
Is upside down.

So unless anyone has a major issue (other that fuel heating or air in the system) I will run with what I have sketched up above and see what happens.

Your comments have been really helpful and made me reconsider a number of aspects that I had rejected initially.

Thanks

Garry

[DaveEFI]

Ah - I assumed the square section was for insulation.

[stevieturbo]

I think the square section is just easier and cheaper to manufacture. Cossies were the same...although oddly their stuff was brazed together too which made it a ballix to weld fittings to !

And generally dead ends are intended to keep the fuel cooler, as in operation fuel is not continually passed through the hot rails then back to the tank.

Cool fuel from the tank simply gets pumped to the rails and into the engine

First key on and turn will usually see a large injector pulse to either wet the manifold walls and/or help purge any air that might be in the rails. So not any real concern either.
Most modern cars these days have their rail dead ended anyway. Seems it must be better/cheaper for emissions or whatever, but it is very very common.

I run 4 rails on mine, 2 inj per cylinder. To simplify plumbing I ran 2 as full flow as normal with an additional 2 rails that are dead ended. Never had any issues in the 10-12 years or so it's been like that.

Some aftermarket regs you could simply flow through then to the rails that are a dead end, or you could tee the reg off to the side and to the rails. Either or really, whatever is easier or neater for you.

[minorv8]

Garry, the bleed may not be a bleed but a port for checking the fuel pressure ?

[stevieturbo]

Correct it is not a bleed port.

[garrycol]

Yes it would not be a good bleed port as it only does one side and is a bit low down. Reading the workshop manual on this, other than indicating there is a Schroeder valve in the system there is nothing about bleeding or pressure testing.

Cheers

garry