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MG MGB GT V8 Factory Originals Technical - EFI fuel set up design - too simple?

I am intending to convert my CB carb’d MGB Rover 3.5 V8 to the Rover 3.9 EFI . I know very little about EFI set up (most of it learnt from the archives!). Please can I ask the experts to comment/criticise on my proposed set up which seems a little too simple. I would like to keep the original petrol tank and not have to sort out welding etc.

Use early petrol tank feed with existing piping to feed a red top Facet pump; this feeds in to a large (half litre) fuel filter. Both items mounted in the RHS boot. Run pipe (not sure what diameter) to fuel rail in engine bay. Return pipe (original MGB fuel line?) back to late sender unit in to tank.

The idea (cannibalized from a design by Peter in OZ) is that the large fuel filter acts as a swirl pot, minimising on parts & pipe work and not touching the petrol tank. Please can you tell me if you think this will work or if there is anything I have missed out.

R Weston


having had great difficulty in sourcing a swirl pot tank when I did my Fi conversion, I was interested in the 'potless' solution.

I don't think the Facet pump will deliver sufficient pressure to the injectors, you will need a fuel injection pump.

The swirl pot is on the return line, I have to admit I don't know why it's necessary ( probably is'nt).

Small bore central heating pipe (obtainable in a roll from B&Q ) is the fuel pipe I used out and back.

You will have to watch the route you take, I originally ran my low pressure feed over the wheel arch
to the pump, and it had difficulty 'sucking'fuel to start up when the tank was low, it's now mounted just in front of the tank, on a level with the feed pipe.

Good luck with the conversion are you using flap valve or hotwire ? I have the former, but am considering changing to hotwire shortly, so may be selling the flapvalve system.

Michael barnfather

Frank is going EFI but is having probs fitting under Bonnet.

Frontline have a tank with swirlpot.


Only because he is determined to fit the bonnet designed for EFi, (the RV8)!

Michael barnfather


Thanks for your comments; in response please can I ask a couple more questions: If the Facet isn't up to the job can anyone recommend an aftermarket affordable pump/regulator that will work?

Re the swirl pot, I thought that this was to provide a constant fuel supply in cases of hard cornering etc. where the pump may pull up air. It it on the pressurised return what is its use, its too late by then? I thought that the large filter in the feed was a good idea.

Re: pipework. If I mount the pump in the boot above the tank will this be OK? It will have to suck a bit. As I have twin 6 volt batteries (new ones!) if this was unacceptable I would have to mount it in a similar place to the SU which isn't ideal.

From memory small bore CH pipe is 8 mm which I guess I can get some fittings to the tank. Is there any use for the original pipework that is in good nick?

It is the Hotwire version that I am planning to put in. When I have sorted the fuel I will move on to the electrics complete with its own wiring harness!
R Weston

You need 40 psi which you will get from the Bosch pump used for the RV8 and others. It needs to be mounted outside the car at the same level as the bottom of the fuel tank and must have at least a 15mm feed. The swirl pot needs to be big enough to supply the engine throughout a long bend in the road when you might otherwise lose suction. Depending on your driving style this might be as small as .75 litres. After the pump and the inline filter the diameter of the hose needs to be the same as the fuel rail connector (8mm if my memory serves me well). You need to allow for an inline fuel filter - the RV8 uses one of two - either a large push on or a smaller srew connector which was supplied by Landrover (and is still available as a conversion kit) for the 3.9 RR.

At 40 psi - all the connectors need to be A1 - you can use copper tubing but you might be better protected in a shunt if you follow the Volvo example and use double wire braided hose. The pump sits on the side of the battery box - the swirl pot/filter either behind the axle or in the space vacated by the second battery.

No you do not need a swirl pot but if the Bosch pump runs dry it will wear itself out very quickly. I suspect that may be true of others.

..and yes you have missed out the interesting part - the FI wiring.

Good luck

You REALLY need to mount the pump on a level with the bottom of the tank, with as short a run of 'low'pressure pipe as possible, as the Bosch pump is useless at sucking. All my EFi parts were from the Rover Vitesse (V8), I've put the punp on a bracket behind the back axle, snug up against the front of the tank, and the low pressure pipe is only a few inches long, around the corner from the tank outlet to theoffside front corner of the tank, then central heating pipe carries the fuel from the pump, over the centre of the axle, and through the transmission tunnelto the filter which is on the nearside where the pedal box would be on a LHD car.,then to the back of the fuel rail.

Roger is right about the connections, I'm running a high power pump with variable rate regulator, and have had quite a lot of problems over the years with fuel leaks, I still go round the Terry clips regularly checking them for tightness ( and invariably the one which leaks is the one underneath the back of the car on the pump !)

Michael barnfather

I am getting confused? I thought the idea of the swirl tank was to prevent fuel pressure drops on long turns etc, when you may "suck air" from the main fuel tank. It does this by acting as a reservoir for the pump. Surely that means that the swirl pot (or big cannister type filter) should be between the main tank and the fuel pump. The swirl pot should be fed by a separate (low pressure?) pump directly from the fuel tank and then the high pressure pump will "suck the fuel out of the swirl pot. You can then put another filter in the high pressure feed to the EFI.
Am I way off on this?
Tony Bates


It is very easy to cut a hatch in a new tank, fix a swirl pot and re-weld the top of the tank; I used a swirl pot from a scrap Granada in an early type bolt on tank.

I use a Bosch pump, it has the same OD as the SU pump and fits perfectly in the original bracket, the bracket is on the side of the battery box with the pump as low as possible as Mike suggests (but mine is in front of the axle). I have an LP filter is the line from the tank to the pump and a HP filter above the pump. I used 8mm seamless stainless tubing throughout and I do not have a larger tube between the tank and the pump.

I haven’t had any leaks but I wouldn’t run any fuel lines, pumps or filters inside the car (or boot) in case there was one, better to leak fuel on the road than fill the car with petrol fumes. I have the wiring harness inside the car and ran the flow and return fuel lines in the saddles under the car following the same route as the original fuel pipe. You could certainly use the existing pipe for the return line, if it is sound.

The ECU is connected to the main wiring harness through a (9 pin) multiplug with 7 wires; Brown, white/slate, white/purple, black/yellow, yellow, orange/black and purple/yellow.

Brown (N) supply from a permanently live connection.
White/slate (WS) supply from the ignition switch circuit for the 'ignition on' signal.
White/purple (WP) output from the relay to the fuel pump - install an inertia switch in the supply to the pump.
Black/yellow (BY) output to a warning light (if required) to indicates system faults.
Yellow (Y) input from the road speed sensor. Sender in the speedo cable is probably easiest.
Orange/black (OB) to earth via a 510-ohm resistor for a manual box.
Purple/yellow (PY) is normally the input from an AC but it can be used for any another heavy load such as the radiator cooling fans.

There is a single white/black (WB) wire near the airflow meter. This is the engine speed input from the negative side of the coil connected to the ECU through a 6.8k ohm resistor within the wiring harness.

Attached to the wiring harness by a two-pin plug close to the ECU is a colour coded 'tune resistor'. Green 446 to 494 ohms for non-cat and 3700 to 4100 ohms for cat.

There is also a plug with four wires. Black/slate, white/light green, white/pink and white/yellow for a Rover diagnostic unit to be plugged in and any system faults read.

There are two standard relays, the main system and the fuel pump and plus another relay for the AC control (fan timer).

The Brown, White/slate, White/purple and White/black must be connected for the system to work. You must also have the correct tune resistor but it will work without the road speed sensor and the Black/yellow and Purple/yellow are not essential either.

Hope this helps.

Geoff King

Thanks gents four your comprehensive replies. On the assumption that the existing low pressure pump was adequate and in good condition for the 3.5 (and my style of driving), would it be acceptable to keep this pump and have it feed a remote swirl pot mounted in the engine bay? This would eliminate the need for the long runs of high-pressure piping and the risk of the high-pressure pump running dry. It would mean that the H-P pump could be mounted under the bonnet with a feed from the near-by swirl pot through a high pressure filter to the fuel rail
R Weston

Tony - you are not confused - there are many ways to skin this cat and debateably the intermediate reservoir between the tank and the pump is easier than fixing a trap inside the tank.

As michael says - the Bosch pump is useless at sucking and really needs a gravity feed - hence 15mm pipe to match its intake nozzle or 8mm like the HP line but accepting shorter pump life. (Been there - got the teeshirt).

For those confused about the pump position and the bracket mentioned by Geoff - early 1800 cars had SU low pressure pumps on the side of the battery box - because they regularly got wet, the factory moved them so that the electrical gubbins could be inside the car. This latter position is too high for a gravity feed so the pump needs to go back to the original position. Fortunately the HP pumps needed for FI tend to be watertight.

Have you put the engine into the car yet or are you still working out plans. I think you are being very optimistic about having the space in the engine bay for a swirlpot. Also I'm not sure how I feel about having a reservoir of petrol amongst all of that heat and vibration and in the "line of fire" so-to speak. My swirl-pot was taken from an old Sierra and welded into a new tank. It was easliy done and works very well. This was done on a suggestion from Roger Parker - although I do believe that most people have remote swirlpots - never in the engine bay though.

Tony and others.I have experimented with high volume low pressure pumps that are located in line between the fuel tank and the high pressure pump. The low pressure pump feeds the high pressure pump. I use a non invasive fuel pick up that has a swinging tube that moves with thrust and braking and requires no intrusion into the tank sheet metal.I have had outstanding results for such a simple system. Holley sells a good high pressure and low pressure pump for these purposes. Dann
Dann Wade

1965-1969 style gas tank with the sending unit from the 1977-1980 car. This gives you an inline feed from the tank, and a return line from the fuel sender. I only really had fuel sloshing problems when I was VERY low on fuel. If you were really worried, race shops usually carry foam blocks that have very little mass, and keep fuel from sloshing around through a tank. You could probably squeeze those in the holes of the tank.


A little late to the party, but below is a link to a page with illustrations of a surge tank setup and detailed instructions on how to build one.

A really terrific site BTW, with lots of project pages. SDS offers a really inexpensive no-frills EFI & Ignition controller.


Brian C.
Brian Corrigan

R. western,
Beware of that idea of mine,
The theory was that the high-pressure pump ran in a circuit, and the low-pressure pump would top up the filter (AKA "swirl pot") that was in that circuit. Problem was that as the fuel circulated through the hot motor compartment, it (obviously)got hot and the vapor pressure of petrol at about 37 degrees is about 80 KPa, more than enough to switch off the low pressure pump (salvaged from my old SUBARU). Fuel filter empties after about 10 minutes, engine stops. Wait a while, vapor pressure drops, low-pressure pump activates and the cycle starts all over. At least that's what I think was going on.
The only way I could get that to work was to run the low-pressure pump in a continuous circuit, all the time. Two circuits with the large filter joining them This was noisy and just plain messy.
Eventually after having a swirl pot very expensively welded into the tank and almost emmediatly accidentally destroying that very expensive tank( jack slipped off diff') and other trials and tribulations I found (as Justin says) that you don't need a swirl pot. If you have the earlier tank with a fuel pick up separate from the gauge sender, then buy a very late sender, that has its own pick up i.e. two fuel pick ups thatlocate very close together. If you have the later style tank just remove the sender and add on a second pipe. It's important that the ends of both pipes be very close together. After I put in the new tank (with late sender) I was not able to get the engine to stall with only 7 litres in the tank.
You just don't need a swirl pot. See the thread "swirl pots, who needs them?"
If you must have a swirl pot then maybe use a water/fuel separator from an out board motor boat (see thread below), or possibly instal an "in tank" pump from a VW (golf, passat etc..). These come with their own swirl pots attached and are ideal. With the VW setups you will need to make up some sort access hatch about the size of a bread and butter plate, it'll be obvious when you see one.

ps. You really , really need a pre pump filter if you are going to run an external pump.


That is a very interesting site.......I notice that the system has been used on a Rover V8 engine....I would be most interested to find out how easy it is to fit and tune, as it dipenses with the airflow meter, and is programable it would result in improvements in both performance and fuel economy.
I wonder if anyone in the U.K. has tried it.

Michael barnfather

So... is the ultimate set up as follows.
Early fuel tank with fuel pick up.
Late model sender unit with fuel pickup.
Fuel goes from the tank pickup to a low pressure/high volume "sucker" pump, then to a marine canister style fuel filter/water separator like above.
The output of the filter then goes to the high pressure "pusher" pump and then to the engine.
The return from the EFI goes straight back to the sender pickup in the tank. The reason that the return doesn't go to the filter is that the fuel will be hot (per Peter's comments).
Have I got this right?
Tony Bates

No, you need to vent the filter back to the tank as well so that any vapor in it is purged. A small line with an orifice would work, I simply pinched the line with visegrips.

Jim Blackwood

Right, I now know what design I am going to follow and if I have problems I will adapt.

I have the early tank and will connect a low pressure filter in line to the externally mounted HP Bosch pump (can get one new for £79) will connect this to wire braded fuel hose to HP filter and then to the Hotwire set up that I am collecting this weekend.

The return feed will be via the sender (as per Peter & Justin). I will also investigate Justin’s idea of some small foam blocks inside the tank where the pipes enter to reduce fuel movement on sharp bends when low on fuel so as to avoid the need for a swirl pot. If this doesn’t work I will add a pot.

Many thanks to all contributors; I will let you know how I get on!


PS. Has anyone found a good website for RV8 spares/part numbers to buy on line?
R Weston

Richard - foam - essential for racing - but not good for road vehicles.

You need a lot of it to be effective - it breaks up during introduction and cloggs your filters - it turns to mush with certain types of fuel and it interferes with your fuel guage sender OTHERWISE it's great !

The large RV8 HP filter used as a pre-pump filter will get you started.

Good luck

Ahh, a change of plan - no foam. Roger just to confirm my understanding do you suggest the HP filter should go between the fuel tank and the pump (and nothing after the pump)?

I was going to have a LP filter before and an HP after the pump.


R Weston

So are you saying that you don't need the low pressure pump to "suck" the fuel out of the tank? From Richards's comment it looks like the plan is:
Early tank
LP filter
HP pump
HP filter to EI
Return back to sender in tank

Tony Bates

Yes the large RV8 filter before and after the pump. On the LP side it is as much a tank as a filter, on the HP side you have the option of using the later smaller filter used at the end of the RV8 run (and by the 3.9 RR) but you would need to get the screw connectors from LandRover (the £££Kit).

Any filter on the LP side provided it holds a pint or more and has a reasonable size connector bore. Just secure it well away from the axle.

Good luck - it's such a worthwhile conversion !

Hi Roger,
So if I put a "big" filter on the LP side, will I or will I not need a LP pump to fill the filter. Will the HP pump have enough "suck" on it's owm?
Tony Bates

Just a word of caution regarding using a late style sending unit in an early tank. I have an original tank on my '68 and the late style sending unit did not fit in it. This probably does not apply to replacement tanks as many people are using this unit. FWIW

Scott Costanzo

Tony - LP PUMP - the answer depends on the position of your HP pump - if it is level with the bottom of your tank, and the bore of the supply to the filter is 10 or more (ideally 15mm) you would not need a second pump - even if the bore was 8mm, the Bosch pump will cope but it's life depends on how hard it works.

I should be interested to hear if you do decide to instal a LP pump - the choice would be important - the OE SU pump was the always the weakest link on the MGB -

You definitely don't need a low pressure pump provided the Bosch pump has gravity feed,and doesn't need to suck fuel, my V8 has never had a problem since I fitted the pump next to the tank, (or the SD1 I took the system from,) but I did have difficulites when the pump was fixed to the battery box, as the fuel had to be sucked over the wheel arch, as it's just not up to the job.

I still feel mounting it on a bracket between the front of the tank and the axle is the ideal position, I've only got about 6" of low pressure pipe at tank bottom level on mine.

Michael barnfather

Give it a shot and see, nothing to lose since you have to buy at least one large fuel filter because you will need a fine filter somewhere before the injectors no matter what you do.I got my big 500ml filter at Kmart cheaply. If it works you're laughing, let us all know. However if it (filter) creates too much suction placed prior to the pump (very noisy, sounds like an angry wasp!)then you can use this large filter on the high pressure side some where before the fuel rail. Then go and buy a special fuel injector prepump filter (which is just a piece of fine plastic mesh in a cylinder about the size of a D size battery), they cost about $15. These have a large inlet and outlet and flow easily. If you are confident that the filter on the end of the fuel pick up is good enough you may feel that is enough, your option/risk.
From the new sender pick up, I have about 1.5 meters of half inch line up over the back axil, the fuel injector pre-pump filter in a loop of the fuel line (vertical orrientation to prevent vapour bubbles), then the pump at the front/bottom of the battery compartment, then thinner fuel line up to the engine compartment, the larger finer filter, the fuel rail/injectors, then back to the tank via the old pickup.
For the first few minutes the pump will be noisy while it sucks air out of the half inch line and establishes a siphon effect, then it should settle down. Mine is still audible with the roof up but not when down. If you are after dead quiet, then go to an intank type of pump maybe.
I would guess my long lenght of half inch fuel line acts as a kind of long thin swirl pot.

Just a PS Frank
Got to agree with Roger ,
The EFI MGB V8 is just amazing; I can't get over how right it is. Fabulous classic sports car looks, great reliability, huge acceleration, lots of fun and just great to burble about in at low speed.
Even the fuel economy is great.
And as an added extra People keep leaving notes on my windscreen offering to buy it, which doesn't hurt the ego at all!.
There's just no Bad

I wonder why Rover doesn't do another retro release like VW beetle or Mini?, It'd go gangbusters with the right advertising.
The RV8 was OK but it was too soon & they tried to update the appearance (non-retro, no chrome visible at all!) & did nothing about the rear suspension. Not that I'm crititizing the live axil, it's fun but dated.

This thread was discussed between 29/09/2003 and 08/10/2003

MG MGB GT V8 Factory Originals Technical index

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