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MG MGB GT V8 Factory Originals Technical - EFI revisited
|3.9 Rover V8 EFI into mgb roadster - I have seen various threads advising the fitting of an EFI Sierra swirl-pot into the B tank, however, has anybody fitted the in-tank Sierra EFI fuel pump as well? - This would seem to be a neat solution or am I missing something? Any suggestions gratefully received ... Andy|
Why do it the hard way?
-From late model sender ($52.00) plumb a fuel line to a large filter ($20), from filter to small high volume low pressure roller vane pump ($100 Australian).From low pressure pump to high pressure pump ($150) thence to engine. The return line runs to the tank "pick up" (now a return) line.
Standard off the shelf parts. This has worked flawlessly, quietly, for at least 50,000 km so far. On occasion down to less than 7 liters in the tank and fuel system. No sign of fuel starvation to the injectors ever.
The big filter protects the pumps and injectors, and acts as a very effective antisurge tank.
Jaguars use a similar twin pump set up
The smaller low pressure pump is made by Pierburg
and is called a "universal autosuction rollervane pump which may be used universaly".
cost $95. It developes good suction and can keep up with the larger high pressure Bosh pump.
It developes only 0.5 barr at the outlet end, but is able to draw up to 0.5 meter comfortably (they claim). It does draw through a large EFI filter up into the boot OK.
Its the one bottom left of the photo. Bottom of the page, fuel supply.
Why the need for the feeder pump?
Fuel is the opposite of water. It has a low surface tension and a high surface vapour pressure. Some of its components start to boil at 20 degrees celcius. This means that fuel doesn't siphon at all well. Vapor bubbles can form under suction (vapor lock, noisy pump etc). Also the hot fuel from the engine rail must go back to the main fuel tank to either redisolve all those bubbles, or vent the vapor through the tank vent system.
|Here is a ready to go filter:|
A late model MGB fuel gauge sender (the one with the fuel pickup,part #ADU3218). There's nothing stopping you removing the old sender to a safe distance and putting in a return line. However, this makes this sender non standard and if you need to replace it you canít do so speedily. I have had to replace my fuel tank in a hurry once, by the way.
High pressure pump (usually a Bosh one, $150, #0580464070)
The low pressure pump is made by Pierburg
and is called a "universal autosuction rollervane pump
As far as I can tell itís Pg 75. Part # KP 7.21440.53.0 or KP 7.21440.51.0 there doesnít seem to be any difference. The guys I got mine off called it part #12001.
Many of the local GM cars run a small feeder pump attached to the fuel gauge sender. I don't think this is as good as having external, easy to get at and change, pumps protected by a filter. Prior to fitting the peirburg pump, I once tried to run without a filter at all and lasted less than an hour before damaging the bosh pump. Now I actually carry a spare bosh pump which I've never had to use, but I know what will happen if I leave it at home!
|Thanks for your suggestions - I was trying to assess the neatest solution and not necessarily the easiest. I have the equipment to modify a tank (new obviously!) and the combined swirl pot/pump would seem ideal. I intend to relocate the tank and also move the sender/pickup from the side to the rear of the tank to accomodate a twin pipe exhaust system. However, your suggestions would certainly be easier and in the event of a pump failure easier to fix! |
Cheers .. Andy
|There are quite a few combined EFI pump and swirl pot set ups in the Peirburg catalog. Just find one that is the best height. I was looking at a Golf one at one stage. As you can see, the pump comes already installed in it's own plastic pot and ancillaries, with a big lid. All you would need to do is make a flange to match (or cut one from a donor tank with some tin snips. Or you might look at using a polypropylene cutting board to make a flange out of and fix that to the edge of your hole.|
Be wary of second had ones from a wreck, if the car has undergone strong deceleration(i.e gone smack into a stationary object, not unlikely at a wrecker)the plastic pot may have broken free of its lid, as I found in the case of the golf.
You are unlikely to find an EFI tank that is the same dimensions as an MGB one. I did once see photos of a rangerover tank installed in an MGB. And I do mean in. The guy cut out the bottom of the boot and the top of the tank was level with the rails, ie up two or three inches. Quite a good solution as long as you are prepared to wear the smaller boot.
Absolutely no reason not to use an intank pump - in fact it is the neatest . Jetta pump is ideal and has been used in the States.
Ideally if you follow this route, weld a small dip in the bottom of the tank so that as much fuel is used as possible.
Another way of doing it is to get hold of a Frontline Costello aluminium tank which has the swirl pot already built in and of course bolts straight onto the B. It is made by Tim Fenna in Bristol, but last I heard he had run out of them. With this tank you will need an external pump - Sytec is best, fitted to the lower edge of the battery box. High pressure pumps do not lift very well.
Unless you have absolutely no option, I'd avoid the low pressure feeding the high pressure pump - you still need a swirl pot and its one more thing to wire in and one more thing to consider, although using a solid sate LP pump should not give any trouble, but once assembled, the set up works well. In theory, this is better than any other method as the HP pump will always be fed and have less work to do.
If you are considering a twin exhaust, then you might use the tank already made by MGOC for this purpose. You will need to do more than move the sender on a standard tank - a portion of the tank needs to be cut out.
With the twin pump set up you don't actually need an additional swirl pot, the big (cheap or otherwise)in line filter forfils this role. The Low pressure feeder pump needs to be a roller-vane pump just like the main HP pump, except that it has larger (fewer) vanes. It is designed to run continuously. It is not a diaphragm pump, which would wear out pretty quickly in that application.
However each to their own. People who go around putting big motors in MGB's usually have their own final outcome pretty firmly in mind.
The main downside to the in-tank pump is that it's a lot more work and you can't buy a replacement tank if you need to. Other than that it's mostly plusses.
I have had to replace my tank twice. Once the jack slipped and punched a hole in the tank. I had just had a swirl pot installed in it at great expense and trouble a few days earlier. It turned out that this accident was just as well. The Bayswater based "expert" who had installed it actually had the very small/shallow "pot" isolated from the return line, despite me giving him a photo of what I wanted! (Be warned people of Melbourne) The other time was that it was a faulty tank that leaked around the fuel uptake/return.
|I used the Jetta swirl pot/pump in my tank, fits very well. Really like the end result.|
|You could put your access hatch under the spare wheel.|
|I didn't want to cut my boot floor so took this approach.|
|Swirl pot and pumps|
(MGB K-series EL5)
This thread was discussed between 09/11/2007 and 24/11/2007
This thread is from the archive. The Live MG MGB GT V8 Factory Originals Technical BBS is active now.