Fuel Tank Replacement

[thebrookster]

Well, I have succumbed to the usual problem of rusty particles blocking my fuel system.

I know I can have the tank cleaned and proofed, and I may well do a temporary job on the tank to keep the car running, however as I intend on going to EFI anyway I am looking at getting a new custom tank made with swirl pot etc built in, prob in either stainless or Alloy.

Has anyone got drawings (or tanks made) for the Mk1 saloon, or do I need to design my own? Or possibly got a drawing of any other tanks that can be adapted (ie like spitfire tank which is similar).

Cheers,

Phil

[Alec]

Hello Phil,

if you are going to have a tank made there's little point copying a Spitfire tank, copy the saloon tank is better surely?

I think that practically an aluminium tank is better than stainless steel being easier to form. My tank is out of my car at present so I could take some pictures and measurements if you like? Presumably if you have it foam filled you won't need the internal baffles?

By the way there's no difference between a Mk 1 and a Mk 2 tank unless it's a P.I. one possibly. (I don't know if some MK 1s didn't have the external swirl pot?) Certainly I have a MK 2 (p.I.) tank in my Mk 1.

Alec

[thebrookster]

Hi Alex,

My apologies, I have created a slight mis-understanding there!

I am not intending to copy per sae a Spitfire tank, merely use any available drawing as a guide for designing a saloon specific tank.

Basically I wish to make something that contains everything inside, so I don't need separate swirl pots etc, and can be an almost direct replacement. The reason I suggested spitfire tanks was due to knowing the rough shape is similar to the saloon tank I have.

I had mine out yesterday and roughly cleaned it which has improved matters for the time being. I like the idea of the foam inside to reduce baffles, I shall have to do some research before putting pencil to paper!

Cheers,

Phil

[Jonathan Lewis]

By the way there's no difference between a Mk 1 and a Mk 2 tank unless it's a P.I. one possibly. (I don't know if some MK 1s didn't have the external swirl pot?) Certainly I have a MK 2 (p.I.) tank in my Mk 1.

At least some (if not all) later Mk1 PI saloons had the Mk2-style tank with internal swirl pot and CAV diesel-type filter in the boot.

as I intend on going to EFI anyway I am looking at getting a new custom tank made with swirl pot etc built in.

If so, seriously consider having the outlet port made so as to be capable of accepting a larger fitting than that used by Triumph; the standard 5/16"ID outlet is not really big enough for the Lucas PI pump, and certainly a potential source of difficulties for the Bosch-type pumps with their greater flow requirement but lesser ability to suck...

[Alec]

Hello Jonathan,

while I wouldn't argue about a larger outlet, my P.I. is set up with quite a bit more fuel demand than standard and I haven't experienced any 'lack of flow'. I'm using a Lucas pump so Bosch pumps are not something I know about. However if their flow is considerably more than the Lucas they are just dumping more fuel down the by pass circuit as metering unit flow is determined by demand?

Alec

[Jonathan Lewis]

Hi Alec,

In terms of fuel supply to the engine itself, the original fitment Lucas pump should be able to support pretty well any reasonable state of tune on a 2.5. The issue, as you rightly note, is the degree of throughput - 16GPH for Lucas, 25GPH for Bosch. Whilst most of this is simply recirculated to the tank, problems arise when the demand from the pump approaches or begins to outstrip the natural flow from the tank outlet, leading to cavitation in the pre-filter (if fitted) and pump itself. There is an interesting article on the Revington TR website (http://www.revingtontr.com/shop/downloa ... 0PUMPS.pdf) dealing with fuel feed arrangements on TR5/6 cars fitted with Bosch fuel pump conversions, which gives some observed flow rates from the tank with various different outlet arrangements.

Having chosen to stick with a Lucas pump (albeit re-sited to the offside of the boot in order to get it away from the rear exhaust box and so minimise ambient temperatures), I've also kept the CAV filter as I believe that it provides filtration to a finer degree than many of the available alternatives, but experience tells me that fuel cavitation in the filter head itself remains a risk under high temperature conditions, especially with anything less than a full tank of fuel. Hence my use of a low-pressure high-volume booster pump between tank and CAV filter to maintain flow at all times and so ensure a light positive pressure at points where cavitation might otherwise occur. With a larger diameter feed pipe to begin with (3/8"ID or even 7/16"ID), I suspect that the need for such measures would be reduced or even eliminated.

IMHO, of course

Regards,

Jonathan

[Alec]

Hello Jonathan,

I hadn't realised the flow of the Bosch pump, slightly more than 50% than the Lucas, all of which extra flow will be going down the return line, to me, is not an ideal situation.

In this day of electronics I wonder what it would cost to have a pressure sensed variably speed control of the pump? Obviously more than a simple pressure relief valve, but seeing some of the complicated systems that people have used with Bosch pump set ups, some seem to take up half the boot?

Alec

[Jonathan Lewis]

I hadn't realised the flow of the Bosch pump, slightly more than 50% than the Lucas, all of which extra flow will be going down the return line, to me, is not an ideal situation.

On the last car I had with a Bosch in-line EFI pump fitted as original equipment, the pump was located in the boot and sent its entire output to a pressure regulator located on the inlet manifold injector rail, with surplus being returned from there to the fuel tank adjacent to the boot... Mind you, the injection system was Bosch L-Jetronic working at 36psi rather than the 106psi of the Lucas PI system

In this day of electronics I wonder what it would cost to have a pressure sensed variably speed control of the pump?

I think that some modern electric pumps for carburettor applications have something similar, but whether it could be done on a high-pressure high-volume injection pump at reasonable cost, I have no idea. I seem to remember reading that early jet engines were equipped with a fuel pump employing a similar principal but accomplished by entirely mechanical means, but would imagine that associated levels of complexity and cost must have been very high...

[Alec]

Hello Jonathan,

it would depend on whether there is a high volume unit being made for another application, that should be quite reasonable.

Incidentally from the Revington site the Bosch pump is three times the current draw of the Lucas but a mere 50% greater capacity, so would appear rather inefficient. What type of pump is it?

Alec

[Jonathan Lewis]

Hi Alec,

The Bosch pump is of roller cell design - conceptually not unlike the oil pumps fitted to 'our' engines, except for the fact that instead of having lobes, the eccentrically-mounted inner rotor has a series of rollers in spring-loaded pockets that effectively provide the pumping action as the rotor assembly rotates.

Actually, a pretty good piece of kit when installed as intended; many of the issues encountered when applied to Triumph PI conversions relate to shortcomings with the detail installation, such as inadequate fuel and current supply, or use of pump models intended for low-pressure EFI set-ups rather than the mechanical Bosch injection systems such as K-Jetronic.

Regards,

Jonathan