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MG MGB GT V8 Factory Originals Technical - Relocate fuel tank

Relocating the fuel tank.
I've often thought that twin fuel tanks located essentially where the batteries are whould do well. This would move a variable weight infront of the back wheels and help with over steer. It would also allow the spare to be dropped down into the boot floor six or seven inches into the space previously occupied by petrol tank. Only worth thinking about if you were buiding a custom tank of course, as some people do. Any thoughts?

How much petrol do you think they might hold, the standard MGB tank is just about adequate for touring....I can get just over 300 miles of motorway cruising on mine before my nerve cracks, a few extra gallons would be very acceptable.

The main problems would be filling,(the Triumph Spitfire had a filler on the rear scuttle, that would be the logical place I suppose), and battery re-positioning (perhaps in the boot somewhere ?).

M Barnfather

I believe that the plastic battery bin boxes hold about 2 imperial gallons (2.5 US gallons)so the total will be of the order of 4 UK or 5 US gallons.
Tony Bates

This is one area I have been thinking about.
My thoughs have taken me to the Miata gas tank which is in the midle. The trade off is with the battery which would have to be relocated in the trunk. I have not calculated the advantage of the gas and the battery weight swap.

Bill Guzman

Hey, guys, check this out!

Pretty neat, eh?
Dan Masters

Hi Dan,
Am i right, a center filler and I like the rear lighs, have you integrated the reversing lights into the tail lights where the reflecter normally is?
Tony Bates


Yes, it is a center fill cap. Here's a another look at it:

The tailights are just stock early MGB lights, and the "reverse" light is just a reflection of the camera's flash unit. At this point, the car has no wiring installed. I believe the owner (it's not my car) plans on not having back-up lights.

Don Marcott, of Wayland, MI, is doing the body work, and Ted Lathrop, of Fast cars, Inc, is doing the V8 installation conversion. This is going to be one fine car when it's finished. Don and Ted are both superb craftsmen.
Dan Masters


Any chance of a picture of the inside of the trunk? I'd like to see how the filler pipe attaches to the tank.

Simon Austin


No, sorry, no pictures of the inside. When I took that picture, the pipe wasn't fitted yet. When the car is finished, I plan to do an article on it for the Newsletter, and I will include a pic of the fuel pipe.
Dan Masters

An interesting thought there which I must admit I had not considered.

Twin tanks would mean relocating the battery as already mentioned...perhaps to the engine compartment which would also put it closer to the starter.

Some sort of flow channel to allow fuel to go from one to the other would side step the need for a central filler and allow the cap to be on the side of the car somewhere just ahead of the rear wheel arch which would alleviated the need to drag the fuel pump lies over the rear of the car and possibly damage the paint work.

Just my 2c,

Cheers , Pete.
Peter Thomas

yeh, pretty much thinking about putting the battery on top of the passenger foot well anyway, which got me thinging about all that space not being used.
Also while on a curving freeway on ramp the other day I hit a slippery patch which got me thinging about oversteer (420 degree spin!).
Tony, the way to go would be to pretty much remove the battery brackets (in my case one)and make up squareish sort of tanks to use all availiable space. Because of the greater depth I think you would probably end up with more than 40litres. It would not be too hard to estimate, I'll crawl underneath with a ruler. The one on the exhaust side would have to be a bit smaller but msybe thats a good place to put a fuel pump.
Not too sure about state regulations though.

If you had a central filler you would have to have some kind of 'T' junction to fill both tanks simultaneously, plus a balance pipe for the feed....seens very complicated.

M Barnfather


Keep in mind that moving the tank forward may just treat you to a few MORE spins. Lowering the polar movement (putting the heavy stuff towards the middle) will make the car react more quickly to any opportunity to oversteer.


Just crunching a few numbers on this intriguing thought...a container measuring 18 inches wide, 12 inches long and 12 inches deep will hold 2592 cubic inches or about 9.25 Imperial gallons and should fit where the battery box fits and allow some room for the shock absorbers , springs , drive shaft , exhaust pipe and fuel pumps and filters etc.

Two will hold about 18.5 gallons which is around 50 percent more than the standard Chrome Bumper MG tank according to Road and Track.

Replacing the standard fuel capacity with two smaller tanks fitted either side of the driveshaft will as mentioned above change the polar moment of inertia slightly and lowering the spare wheel into the space formerly occupied by the fuel tank will very slightly lower the centre of gravity.

If anyone is actually going to do this it would be worthwhile to fit a drop down door below the rear bumper and give the spare wheel a compartment by fitting a steel panel in the boot to add strength and give a totally flat floor.

Fitting an angled filler pipe would allow the fuel filler to be relocated to a point ahead of the rear wheel , above the chrome side strip and below the attachment point for the roadster convertible top.

Cheers , Pete.
Peter Thomas

Pete, and of course the tail shaft doesn't go anywhere near the bottom of the car. A shaped tank with a small pipe link across the heel board brace. It would probably be easiest to adapt a tank of the right general dimentions. Weld or glass in a tunnel for the tail shaft.
Mike, for the filler I was thinking of just extending the existing, or maybe do it like the old VW's (open the boot). Of course this is pretty hypothetical. Mind you if I was doing another conversion, and had easy access to under the car and needed to buy a new fuel tank (how's that V8 conversion comming DOM?) it would start to look pretty attractive. I like the idea of a big empty boot as well, I think every body tends to resent the space the spare takes up.

Yes Pete,

I ditched the spare ages ago...just carry a gas canister now....don't even bother with a jack.

Mind you, my tyres are in V good condition, and readily obtainable throughout Europe.

Most of our MG driving is continental touring and my better half needs the boot for her essentials.

The thought of 18.5 Imperial gallons is very tempting, we can barely get to Dover from here on a tank-full !

Michael barnfather

HAving a closer look a a few B roadsters at the weekend just passed it would seem possible to run the fuel filler pipe into the newly relocated tank assy from the rear mudguard / wing ahead of the rear wheel arch and into the space between the door lock post and the rear wheel arch thus adding slightly more room to the boot space.

Having the spare wheel where the fuel tank now is would go close to doubling the physical space in the boot and have an added bonus of leaving the remaining space a more useable shape.

Any thoughts on this ?

CHeers , Pete.
Peter Thomas

Pete-yes , should work. It woud tuck the pipe nicely out of the way. May be even put the cap much as per the old Jag's, which had a filler either side behind the rear quater windows on top of the car, ther's room there. The spare could be bolted up under the boot where the tank now is. I've seen many station wagons which do this. Of course if anyone was just after more boot space then they could put the spare through the back of the boot much as the MGA does. Perhaps a carpet cover for the wheel or maybe a false deck. A little reinforcing around the (fairly large) hole of course. Infact you could do this in such a way so that the rear cockpit trim was offset-hinged. In other words when you need the space push the spare through the back of the boot, otherwise the trim folds/locks down and no one is the wiser. That space behind the seats is pretty useless as you only need about six inches of it for roof folding. There would also be a certain golf club/ski carrying advantage to be gained. Irrespective of the tank shift I might just really do this. Invisible, easy to do with lots of advantages.
May be Bill could calculate what moveing the spare forward (and up a little) would do?
I really don't want to abandon the spare as per Micheal. For example when I spun the car the other week I managed to knock the front tire off the rim as I passed (spinning rapidly) over the curb. (I didn't count the 360 degrees when I had my eyes shut by the way!)

Have a close look at the Jaguar XJ6 system. The key to their system is change over valves and a dash (fascia) mounted switch for taking fuel out of either tank as is needed. Good way to go if you are considering 2 separate tanks that are joined by a T in the fuel line FWIW Alyn

There is a Saab space saver spare on Ebay (UK)the 4 bolt wheel bolts right on a MGB and gives a little more
room in the boot (less junk in the trunk) sorry!

Got one of makes very little difference to boot space, they are not that thin in reality.

M Barnfather

To quantify a few numbers on the “removal of the spare wheel from the boot” question some details follow:

The full sized spare is about 24” in diameter and about 7” deep. Removing it leaves a boot space of about 37 “ between wheel arches and about 14” high (over the rear axle but this tapers and also steps down toward the rear) and about 30” deep giving a total volume of about 8.99 cubic feet. Some small additional volume will be found around the wheel arches but that is not counted here. The main flat floor area where the spare now sits is about 24” deep and about 37” between the arches and around 14” deep on average.
The general consensus is about 4 cu ft per person minimum for useful luggage space. This will allow the fitting of at least two hard suitcases measuring 14 x 24 x 18 (about 3.5 cu ft which is a generous size and much larger than any I happen to own) and there is still some space for soft bags.

Removing the full size spare to the redundant fuel tank location keeps the boot free and eliminates having to unpack the boot to change the spare. Also this allows sufficient space to store the full sized spare wheel which has just been removed.
Having a “space saver” spare is not a favoured option here in Australia due to the distances involved and the low speed limitations. Many new car makers here offer a full sized spare at extra cost where a space saver spare is offered elsewhere. In Europe and the USA the situation is different as the population is larger and the towns often closer together on average.

My suggestion is to use the two tank method and a common take off for the fuel supply and a balance tube , as Peter suggested , with one inlet situated on the opposite side to the exhaust pipe. In my opinion having switches and taps to transfer fuel and dual fillers is basically a damn nuisance speaking from experience and is just one more thing to deal with and have go wrong. Others may well feel differently of course and please feel free to go your own way.
If anyone does actually do this I would be most interested to see how it turns out.

Cheers , Pete.
Peter Thomas

This thread was discussed between 29/01/2005 and 14/02/2005

MG MGB GT V8 Factory Originals Technical index

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