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MG MGB GT V8 Factory Originals Technical - Swirl pots, who needs them?.

Swirl pots, who needs them?.

For my 3.9 EFI V8
I went to allot of trouble to set up an in tank swirl pot , external pump. An arrangement wasn't entirely satisfactory (a little noisy, expensive, time consuming etc.).
A while ago, while jacking up the car the Jack slipped off the diff' and totaled the tank (ended up a kind of very expensive banana shape).
Since I needed the car the next day, and didn't have time to mess about welding in tank pumps, swirl pots etc.. I simple went and bought a replacement tank with the fuel pickup included which is all you can get now days, I also bought a very late model sender, the type which also incorporates a fuel pick up. This gives you a pick up and a fuel return, which are very close to one another at the lowest point in the tank.
I put about seven litres of fuel into the tank from a jerry can and drove to the local station to fill up. Feeling a bit experimental, I thought I would see if I could get the motor to cut out by some sudden stopping and starting, cornering...didn't happen. Still hasn't happened, not once.
Either it's because the pickup and return are so close, or because there is about 1.5 meters of half inch hose and a filter prior to the pump which act like a swirl pot. Either way for all you new EFI converters who wish to save a little money, simply buy yourself a late model sender and save messing around with swirl pots for when you get bored.

Additionally despite the fact the pump is sucking through the late modle sender pick up pipe (about a foot of much less than 0.5 inch pipe) the pump isn't any noisier than before, a little less if anything.
Peter

Iam using a similar set-up. When I bought a new tank lastyear I got a deal on a early model tank that had the built in pick-up. That would be perfect for EFI guys. I have not yet had a stall out with that tank, even with some hard racing on 1/2 tank and spirited playing with even less..

I was thinking about making something to mount to the sendet unit, but think it would have been more trouble than worth..
Larry Embrey

That was how I ran my efi before I switched to a fuel cell in my trunk. Early style tank + late style sender = fuel pickup and return lines + the correct fuel sender for most aftermarket gauges. Amazing how these things work out sometimes.

Justin

What about capacity ? Are the earlier tanks smaller than the later ones ?

Mike
Michael barnfather

Mike,
The earlier ones hold more fuel, at least the US-spec tanks do.
Dave
David

I'll keep that in mind in case I have to ditch the battery boxes for the IRS. (A strong probability) Just the battery to worry with that way.

Jim
Jim Blackwood

Mike I belive there were 2 basic types of tanks (correct me if I'm wrong someone). There is the rubberbumper boltup type and the earlier held in place with metal straps variety. Of the rubber bumper type there is the earlier fuel pick up variety (1975-?) and the much later sender fuel pick up type. This much later (more expensive) type had a vapour collection chamber in it which reduced capacity.

Thinking further on this pick up idea, there's nothing stopping anyone from soldering (welding ?)a pick up and return into the old sender,no degassing & welding old tanks or having to buy new etc.
A simple continious loop of tubing (metal) with a hole (or series of small holes) drilled in the further most (deepest point in the tank) end (loop) to to allow ingress of fuel. In fact since the hole(s) is in the side of the tubing there would be a definite suction like venturi effect so there would be even less chance of starvation. Place the holes on the bottom of the tubing and even better. May be wrap a peice of fuel filter around.
Additionaly as the return flow is feeding directly into the intake line that would take much of the "suction" strain from the pump itself and should make it run totally silently.
I did do some experimenting with a small external swirl pot at one stage (I had problems with the feeder pump)and if these high pressure bosh pumps are fed they are completly silent.

The only draw back is that the fuel in the line would get warmer than usual, however it would be being cooled by ingress of fresh fuel and also the lenght of line submereged in the actual tank so it shouldn't get too much warmer. Infact if the submerged line were to be made longer than it need this arrangment would keep the fuel cooler than an external swirl pot arrangement.
This is an idea I'm liking alot.
Can anyone see a downside?
Peter

Note: If your F.I. system originally had 3/8ths steel fuel line terminated at your regulator then you should be informed that a sustained heavy load on your engine could cause a lean out condition when using the original 5/16ths fuel line that is available at the fuel tank. This can also be a real problem in high altitudes. Your return line should be 5/16ths. In normal applications there should be no place in your fuel feed system less than 3/8ths. I thought you would want to know. Dann BCC
Dann Wade

Thanks Dann,
Prior to engine installation I spent a remarkable amount of time (took all day)under the car putting in a new fuel line and return. Led both lines along the bottom of the car where orrigional was, & then up to top RHS of transmission tunnel (well away from exhaust)which dispite the proximity of the RH head had the most clearance. All three lines then tucked in neatly back up under heater Fan (tank vapour line as well).Used Bundy tubing same size as in the car it came from. You're quite right, distinctly larger than the orrigional MG fuel line.
It's just amazing how complicated a shape you get when you try to do it in one section. If I were doing it again I would probably just go along the top of the tunnel and not try to cluster the fuel line with the rest of the electricals etc...
Peter

Very good Peter. You have taken advantage of an open air installation. You may not notice the difference but the cool fuel might just result in a HP gain. Of all the installations I have done I always dreaded running all new fuel lines. It seems that it takes more time than any thing else that is installed. Good luck and good job! Dann BCC
Dann Wade

Just out of curiosity, considering American cars have for decades used 5/16" fuel lines providing fuel movement to the engine by *suction* with horsepower outputs exceeding 300, is it really at all likely that a pump pushing 45 psi to the fuel rail will lean out at any equivalent power output? Seems unlikely to me.

Jim
Jim Blackwood

The purpose of the 5/16" pipes & pump was to keep the float chamber of the carby full, which was in turn a resevoir. EFI systems do not have this resevoir to draw on. That's my way of thinking. Barrie E
Barrie Egerton

That may be. Still, one would think a Dodge 440 pushing a 32' motorhome up a long grade would produce a sustained output in excess of 300 hp for far longer than the float bowls could hold out. Plus considering the main tank is at the rear and is therefore lowered significantly by the grade and all that is moving the fuel forward and upward is vacuum.... Well, that's considerably different from a positive pressure of 45 psi. I have other examples, say a 1970 Olds Cutlass (310-320 hp) at 150 mph sustained for several miles for instance. Granted it could have leaned out a bit but I would suggest that the manufacturers provided for sustained power output. Or just about any vehicle with a towing package and 300+ hp will have to sustaim max output to climb grades in the mountain ranges towing a boat or trailer, but 5/16" was almost always the fuel line size.

Jim
Jim Blackwood

This thread was discussed between 11/07/2003 and 24/07/2003

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