V8 SU Fuel Pump - Winch Challenge

[tacr2man]

If you want a good fuel pump then these work well , I used them to overcome fuel vaporisation problems in petrol engined tow trucks that were vapour locking in the engine driven mech pump when sat still running with beacons on . I mounted them at the tank outlet , and it delivered enough fuel for a thirsty 4 ltr straight six.

http://www.ebay.co.uk/itm/Mitsuba-Type-12v-Fuel-Pump-/370840130690?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item5657cb5482

is it a holley carb on your engine by any chance ?

[smallfry]

I do think it will be vapour locking. It was a really BIG problem on the old Rover P5B (I have got one of these as well) leaving cars stranded in traffic and at the lights. They then had a mechanical engine driven pump with a constant flow return fitted, and it all but cured the problem for the most part, but NOW with the advent of modern more volatile ? evaporation prone ? (dont know the correct term) it is again a problem for many.

It seems to occur more when the car is standing in traffic for a long period, or is stopped and then re started fairly soon. I guess both of these scenarios allow the fuel flow to either slow right down on stop altogether allowing the fuel to absorb more heat and vapourise in places. These engine do seem to produce a LOT of heat.

In your case, revving the nuts, sorry, I mean working the engine hard with not much movement to get cooler air into the engine bay, will possibly cause this, so IMO for what its worth, if you can keep the fuel moving it will help a lot, and dont worry too much about the pressure unless it is too high.

Also, some sort of fuel cooler maybe, but could be vunerable, or insulate the fuel lines ?

[Team Idris]

No, not a holley. Just normal SU's.

The fuel lines run in a 1" bore plastic pipe, with plumber foam tube around that. It's a good fix all around and gives the pipes a little more protection. Its been that way a long time and I fully recommend it

Given above, the tank heat fix could be some thin ally to divert the rad air past the tank. You'd be on a hell of an odd road trip to heat the fuel tank normally, but winch challenge does some odd things to a vehicle, due to the length of time running

Very tempting to have a coil of pipe just under the bonnet fan, on the return pipe? I need to swing it more toward slow "mobile plant" than "car" I think.

I'd go for a proper regulator, but I'd need to set the return restrictor down to point where it always holds back pressure, no matter how low the flow got. But I won't know how low it will get until I'm 2 hours in? And I don't fancy my chances of a return-less system, given the reason it was fitted (and it seems a good way of reducing vapour).

I'm thinking of dropping into a research cycle with it. I'll fit a small pipe clamp to the return, where the rubber hose is inside the tank bund. (I left spare hose loose here for this purpose, which was how we cable tied it easily). Then I can adjust the flow adhoc as we race, so I can see if it is fuel level or temperature related. Then I can drop some time and cash as appropriate.

Thanks for the help,

Steve

p.s. At least it now climbs stupidly steep hills again, which is more than it did at the start of the thread

[Team Idris]

I'm learning a bit more after more work on it just now, and we think this is good logic;

Pressure is resistance to flow, flow is dependant on pump speed, pump speed depends on voltage, voltage depends on the alternator speed and the alternator relies on a dry belt. So blasting through a mud hole with all the fans running kills the fuel pressure. Simples!

This came about because I was beginning to think it was haunted. As I tested the pump with the engine off, the flow kept dropping. Turn off, wait and on again, and the pressure comes back up? Basically I'm flattening the battery

Maybe a volt meter to go with that new fuel gauge

[Team Idris]

Here's a thing that might do nicely on the return line?

http://www.ascoexpress.com/product-item/p/f20b-14-npt-brass-female-to-female-flow-control-valve-4907/

Team mate Terry knew about them. Bloke's like a walking encyclopaedia of mechanical parts

[elbekko]

Could you use a higher pressure pump with a pressure regulator?

[Team Idris]

In one sence I have room to move, as this pump does 7psi and plenty more flow than the durite. (or that I even need)

So lets say I get a regulator from merlin and it does a 4psi max. I still have to restrict the return if I want to reach that 4 psi. And ideally it is an adjustable restriction. (this really is like rubbing your head and patting your tummy). Otherwise a change in the little filter at the front will change the flow charectoristics? So I could have 4 psi, but no return flow. But if I hold it back at the end of the system I get it right at the carb and get return flow? I suppose the point that needs to be 3-4psi is the 'T' at the carb? And if the pre-carb filter dropped a mad 3psi, I'd still be well in, as the pump does 7psi

I might change my mind in a bit

It is coming clearer as I write though; So too much flow, too much potencial pressure, and regulating it after the carb ports feels right for this task..............I need a pressure relief valve rather than regulator, and it is a pressure relief that is blowing off all the time?

[tacr2man]

I think you are creating your own problem , a one inch diameter supply is totally excessive, what you need to do is have a decent flow , the large supply is acting as a heat sink, as it is being limited in flowing by the return restriction . .

A 3/8 pipe is more than sufficient , that would flow enough fuel to run a straight eight petrol engine that was doing 3.5mpg ! I know that from experience!

The landrover V8 standard set up just relies on a restrictor in the return line to ensure that the required psi is reached in the supply line to be bled off into the carb float chambers via the needle valves. I take it when you say that you have SU carbs that these are HIF

( in other words with integral float chambers) as the SU that were on earlier V8 rover cars were external float chamber and not suitable for acute angles , thats why landrover initially used the strombergs on the V8 in discovery and stage 1 V8 . HTSH

[Team Idris]

The inch pipe is a duct. Both fuel lines run down it. I wouldn't need anything as big as 3/8 OD.

Carbs; HIF, originally from an SD1, ran for many a year, before a re-con at Carburettor exchange.

The RRC looks to have had two restrictors, one at either end of the return pipe. One make sense, two is a bit odd?

The valve with stainless steel needle valve is £25. Unless I come up with some genius plan in-between, I think I'll grab one next month

[Team Idris]

It was there and then it wasn't, so I remembered Beaumanor; http://www.beaumanor.com/Products/0001000e002a/VNE02 which ought to be better than a tap.

[Team Idris]

Nothing worked

Needle valve wasnt a needle, just a taper plunger, and its flow control was rubbish. (Hardly better than a lever tap! )

1/4" stainless relief valve that I had lying around is excellent in itself, but 4psi wasn't enough to move the 3mm pin against it's seal

So I went into work today and made two 1/4" bsp ally tubes for choice. I picked the short one, popped a 1/4" fitting in the end, dropped in a ball bearing, followed it with a light spring and screwed a hose tail on to push the spring down. And now have 4-4.5psi, which should be resilient to flow changes, while maintaining good circulation of cool fuel past the carbs