1974 Unibody Triumph Spit6 (with some detours inbetween)

In my GT6 I had a small (maybe 0.5l) swirl pot upstream of the pump with no lift pump. That was running PI mechanical injection and drank like a fish so I think you'll be all right.

Bear in mind that if your using fuel at a significant rate the pump will lower the pressure in your sump/pot and pull fuel down as well as relying on gravity. You need to ensure that there's enough volume for a long bend (1.4l seems like more than enough) and I'd look at how the TR6/2.5PI are plumbed as I remember there being a separate house to bleed air from the swirl pot back to the tank on my system.

Thanks guys, been doing some more thinking about the fuel tank. Might have identified a place for a low pressure pump to sit tucked out of the way, but I've also done a bit of measurement of the space I have for a tank. Rough calculations, but if I make good use of the space I reckon I could fit a good 45l tank in there which would be plenty enough to have an in-tank setup for at least a low pressure pump. Now I just have to decide if I think it's necessary for the weight it adds. Probably, but worth some thinking!

Oh, and scimjim I think the link to the 126 tank's not working...

Thanks man can see it now. Very interesting.

Doubly so because I've found out my current setup still won't fit, even with banjos feeding and exiting the walbro pump. So, I've been looking at designs for in-tank baffles and sumps as I think there's some unused space between the bottom of the fuel tank and the chassis for a bit of a triangular one. I'll likely keep the fuel pump and filter down under the car, but removing the sump should give me enough space for them both. Swapping to a sytec pump should also help with the feed situation as they've got 15mm inlets rather than the 10mm inlet of the walbro which I reckon is a cause of some of their issues with requiring lift pumps.

It may be worth having a look on ebay at "in tank fuel pump assembly" and choose one for your potential rated output - although most have a generic pump with more capacity than most engines require - many of these assemblies can be adjusted to suit different tank depths or buying one and having a look at OEM designs that have to work even when run on a few litres splashing about in the bottom of a tank.

Spitfire update
So, I've started making the fuel tank but not a great deal of progress. Bought an eBay bead roller which works a treat but bends to a worrying degree in use so will need some reinforcement. Will grab some pics when it looks like a bit more than a flat sheet of metal with some creases in it

X1/9 update
So, leakdown tester arrived. Tried it out but didn't read the instructions so managed to junk the bellows (dolt). Luckily, my aircraft mechanic mate came to the rescue and lent me a set they use to test piston engined aircraft (with firm direction to read the instructions!).

Put 80psi into the cylinders and got 76psi (cyl 1), 68psi (cyl 2), 66psi (cyl 3) and 78psi (cyl 4). So leakdown percentages of 95%, 89%, 83% and 98% respectively. Apparently while they wouldn't necessarily be happy with the spread between 98 and 83, the absolute figures would still be airworthy. No particularly loud hisses from the inlet or exhaust, and couldn't hear any bubbling from the coolant tank so don't think it's valves or headgasket to the water jacket. Did sound pretty hissy from the crankcase so best bet is rings. Also tried listening to the sparkplug hole in the adjacent cylinders but decided it wasn't really possible to distinguish between two sets of leaky rings and one dead headgasket.

Any other ideas for testing if the headgasket has gone between the two? If I can work out it's alright I'll probably run it on slightly worn rings for a while until I've saved up for rebuild stuff

Next job was to look at the overheating after a long run on the motorway. While it might still be a leaky headgasket, another idea I had was that the water pump end-clearance might be off with gasket+sealant+manufacturing tolerances. If that's the case that might explain why it can keep cool with the revs up but overheats when idling.

Pulled the pump off and found the clearance was probably a bit big. Difficult to measure as the surface is curved, but the Haynes states 0.8-1.3mm and it was between 1 and 1.5ish depending on which vane I was measuring.



So, did away with the gasket and went for just sealant, and ground the vanes until there was a 0.5mm clearance on all of them (there's a good 0.6mm difference between the biggest and smallest vanes).



Might be a little tight even with the sliver of sealant spacing it out, but it doesn't touch even when hot. Quick test run seems to show an improvement, but without a long motorway run I can't be sure if it's worked 100%. Still, one possible cause crossed off the list

Been chipping away at the convoluted fuel tank and got to the point where I've got the lower tub sorted.




Leaks like a sieve at this point, but will steadily patch up all the holes in the lower section.

Still to make: gated baffles, sump, hole for fuel sender, top panel, inlet, vent, and mounting brackets.

That's quite a construction. I'm impressed. I'll be way beyond impressed if you can get it leak-tight with MIG with that much weld-length...… And water-tight is definitely not the same as petrol-tight...….

Watching with interest - may the Force be with you!

Nick

Latest updates

Welded on some mild steel banjo fittings to the bottom of my tank. Had some packaging issues with the original plan of just having barbed fittings poking out of the side (exited directly into the spring), so I thought I could fit some banjos pointing sideways which will run into some bulkhead fittings and then off under the car. Should make it a little easier to remove the fuel tank in future. Thought about welding some threaded bungs in to bolt the banjos on, but figured one fewer place for leaks was worth it. Also welded up some mounts




Next step was to sort the fuel filler. I wasn't convinced the stock filler would pass IVA so I came across an IVA-friendly aero-style fuel filler. Clearance is pretty tight above the tank so it needed cutting down to about half the barbed length, and the cap will probably need to be removed to get the tank out. There's also probably not enough space to get a hand and a spanner in to hold the teeny tiny M3 nuts once the bulkhead is in place (and the thought of dropping them while trying to do them up gives me nightmares!).

If I hadn't already fillered the rear deck panel I'd just weld captive nuts in, but decided to go for a little captive nut ring which works quite neatly






Lastly, my mate's bought a car and I'm dead jealous (not least because it actually works at the moment!). Some pics from the eBay listing:






E36 coupe with an M62B44 swap, stripped (but trimmed) interior, nice coilovers, nice wheels and stone cold awesome arch flares on the back. Pictures don't do the arches justice, they're kickass. Oh, and an exhaust cutout valve sounds awesome

It's a bit drifty for our tastes, but all the bits are there for a proper track/backroads weapon. Work so far has been taking out what's left of the interior to have a look underneath and adjust the seating position. Found two of the studs were missing so I welded some more in for him.



In the process of removing the hydraulic handbrake (nothing against it really, but it's not the greatest install). Will also de-camber the front a little and raise it up, and soften the coilovers from max-hard. Beyond that and some tidying of the wiring, and replacing the welded diff with an LSD, it's all good.

Jealous.

Thanks man TIG and 1.2mm steel would have made it a lot easier. Mine's 0.9mm to cut down on weight and I've had to use the rest of the structure to pull bits back into shape after welding (you can easily see it on the middle of the trailing edge in the photos above). Worthwhile for me at least as it's about 2.5kg lighter than it would have been in 1.5mm. Still heavier than the old one (8.7kg vs 5.6kg), but that's to be expected as it's a lot more complicated.

TIG torch to gloss over and melt everything back together sounds like a dead useful thing. Wonder if that would work on MIG welds...

Yesterday's progress was in the bulkhead area. The IVA states that fuel tanks can't be in the passenger compartment, or any compartment that's open to the passenger compartment. The Spitfire had a trimmed MDF panel between the two which I'm not certain would fly. Could have rigged up something bolt-in, but it was much simpler to weld one in.

Did some testing with CAD to begin with, and make sure I can still get to various components.



Then made it up in some leftover 0.9mm steel from the fuel tank to keep the weight as low as possible as that area is stiff enough already.



I've still got to box in the area above the diff access panel, put plates above the wheelarches with holes for the wiring loom and an MX5 boot release cable, and make a little access panel to close in the top where the filler cap is, but after that it's done!