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MG MGB GT V8 Factory Originals Technical - Swirl pots and fuel tanks

I'm in the process of converting to fuel injection. Now I am the point, where I need to work on the fuel supply system.
What's the best option for a swirl pot? Buy a new tank with one built-in,(possibly with the pump in the tank), modify at stock tank, or some sort of remote mounted swirl pot?
bill jacobson

First the problems you need to deal with, the reasons why and what. Then the solutions to these problems. Even if you skip to the solutions first, you should read though the reasons why later.
Fuel injection on rovers (and most efi) works by pumping petrol to the engine fuel rail and bleeding off the excess back to the tank. You need a fuel line from and a fuel line to, the engine. Two fuel lines.

-Petrol has very high vapour pressure and low surface tension (exactly opposite to that of water). Petrol-Vapour pressure around 70 odd Kpa at 38 degrees.This causes a few problems.
Petrol doesn't siphon at all well as a result. This means that the pump needs to be level with the bottom of the Tank. Problem is that there is no room anywhere around the MGB perol tank to put a pump. Also High pressure fuel injection pumps are good at delivering pressure, but really bad at suction. It's intrinsic to the roller vane design. This means you can't really rely on suctioning up and over the axle or spring to another location, there is no real siphoning to rely on. The pump will start to cavitate and make a very loud noise and even if it manages to deliver fuel to the injectors under these conditions, will not last too long. Particularly noticible in the summer.
Also high pressure fuel pumps will be destroyed by any debris and therefore any fuel must be filtered. Which makes the poor suction problem much much worse. I tried running without a filter and lasted about three quaters of an hour!
The other main problem is that when the fuel warms up a bit, after passing through the engine compartment for example, the lighter fractions will come out of solution and form bubbles. These vapour bubbles need to be delt with somehow otherwide you have the cavitation problem again. The way this is dealt with is to pass the returning fuel back into the main bulk of the fuel and rely on the petrol tank vapour venting system (charcol canister, petrol cap vent etc)
to deal with whatever doesn't disolve back into solution.

You can get a tank modified to accept an intank pump. This means a bolt on flange needs to be welded into he top of the tank and a hole cut in the bottom of the boot. The disadvantage of this is that it is expensive and if you damage your tank you have to wait while a new one gets alterations made. You can buy a new tank and alter it your self of course. Don't try to weld a used tank Kaboom!
The advantage is that you do not have problems with vapour pressure.
The approach I've adopted is to use a standard tank and a feeder pump as well as the main pump. Peirberge make a small rollervane feeder pump (part number 12001) that can keep up with the high pressure bosh pump. This 12001 pump doesn't deliver enough pressure to run the injectors, but it does suction well enough to pull through a large filter and keep the main pump supplied. The particular advantage of this is that the large filter acts as a swirl pot or anti surge buffer, as well as filtering the fuel without any cavitation problems. I've had less than 7 litres in the tank from time to tme and never had fuel starvation. You can set this up by running a fuel line from the fuel tank to a filter, then from the filter to the peirburge feeder/suction pump and then a line from the feeder pump to the main pump. You can throw all this in the boot if you like. All very quick and easy to set up using off the shelf, readly replacable parts. If you also buy a very late model (1980 for example) fuel guage sender, this has a fuel uptake line incorperated into it. Thats your second fuel line into or out of the tank.
You can also save some money by removing the existing sender to a safe distance from the main tank and putting in your own additional fuel line. solder, off the shelf brass fittings/epoxi seal, welding whatever works.

Another approach is to set up a small external tank , other people can exlain that one.

Here's all you need to know.
Tony Bates

I use a fuel pump from a turbo Volvo mounted slightly above the bottom of the tank. It pulls very well and pushes to 90 lbs. I also use the factory filter, all mounted on the (Volvo) factory plate. Take a trip to the recyclers. I paid $25.00 for the whole rig, am using the recycled pump, and have a new backup pump just in case.

Glenn Towery added a swirl pot to a new tank for me, but I think I could get along with the Volvo filter as a swirl pot.

I have run this setup for over 2 years, about 12,000 miles.
Jim Stuart

word of warning,
I'm told some of the very early tanks have baffels fitted. In this case you can't use the later sender with the slightly larger uptake line(part # ADU3218). Easy to check, take off the existing sender and see if you can see the centre of the tank.
The feeder pump is made by Pierburg in Germany and is called an Auto-suction vane cell pump. Stock no. 12001. It can deliver 0.5 bar when used as a primary pump. It cost $95 Australian (apply exchange rate to get an idea what it might cost locally) The main high pressure pump is a Bosh one pt no 0580464070 and cost $140.
The volvo pump sounds like it might be a better option. New they are about $30 more expensive than the bosh pump.
You could try the set up without the pierburge pump to begin with and if its noisy and you get cavitation then go buy it.

afterthouht- I don't know if the peirburge feeder pump can keep up with the more powerful volvo pump.
you'd need to find some figures on volumes/minute for all the pumps.

Bill, the way I would attack it second time around would be thus:- Use the original pump to feed a filter/surge tank. Then feed the HP pump from the filter. Run a new fuel line (3/8") from the HP pump to the engine via an EFI fuel filter in the engine bay. Use the original fuel line for the return feed back to the pump filter. Run a new fuel line (5/16")from the pump filter into the fuel tank. To do this, I would route the line to the rear of the car & enter it into the boot/trunk then into the metal part of filler pipe . I've got a hunch that this is an MGA conversion, so I'm not conversant with the trunk set up ,but it should be easy to keep the pipe out of harms way.
An external HP pump needs a filter in the inlet side, so the filter I'm refering to serves both as a filter & surge tank.I would guess they hold about a pint of fuel They're used in turbo applications & look like the external oil filter set up only they have 4 ports . This simplifies the plumbing arrangement no end. Mount the HP pump so that it's inlet is below the level of the filter the outlet. This is also a good time to run the electrical lead for the HP pump. Barrie E
Barrie Egerton

Bill, I tried modifying the original tank in my midget to install the GM pump. Works fine except for some fuel starvation problems when the level gets below abou 1/2 and I make a hard right turn. Used the return already mounted on the GM flange and ran a return line alongside my supply line from the tank to the engine. Not a lot of room in a Midget for a swirl pot, so this solution was simplier for me.
As for working with a used tank, I had plenty of time to vent the tank while the car was under construction, but there are two easy ways to make it safe, one fill the tank with water to drive out any gas fumes, or two drop in a couple of pieces of dry ice and let it sit for a half hour before working. Either way, you can make it quite safe to weld on a used tank.
Bill Young

Please take a look at Tony's link. This filter housing is what I used, with a Holley as a priming pump and a high presseure pump after the filter and it works perfectly.

One warning - the fuel filter they supply with it may be to big for you to fit depending on where you hang the assembly. You can't tell from the picture, but that filter is the same size as a regular large oil filter.

If you buy one of the assemblies from the Bronco guys and need a shorter filter, let me know and I can save you the trouble of working out which one fits as I've already been through it.
Bill Spohn

Good info!
I originally was going to modify the tank to accept a GM pump. Similiar to what Bill Young has done.
However I would probably have to modify the trunk (boot) floor, for top fuel line clearance. Since the trunk is already painted body color, I would perfer to leave it as is, if possible.
Jim, do you have a pic of the modified tank with a swirl pot installed? I'm trying to get an idea what the swirl pot itself would look like.
Checking out Tony's link, it appears to be similiar to the systems mentioned above.
Bill Spohn, I assume you are running a similiar system. Where did you find room to mount the filter/acumulator? Looks like there might be enough room in the area where the stock fuel pump is now.
bill jacobson

Hi Bill

I am running FI in my car and used a Mk2 Golf GTI swirl pot. It has the pump mounted in it and site like it was made for the job in the battery well under the car!

Perfect, reliable, up to the job and cheap!

Good luck
Ed Braclik

Ed, any chance you could post a photo of that tank?

Jim Blackwood

If you use only one 12V battery the other side is a natural space for the external swirl pot/filter.

The low pressure feeder pump can be located where the stock SU pump was and the high pressure pump can be placed after the filter - I installed mine on brackets welded to the outside of the driver side frame rail, but anywhere out of danger and as low as you can get it would work.
Bill Spohn

Bill, to set up a swirl pot you will need a feeder pump anyway. The feeder has to run continiously. You will need a reliable pump that will do this. I have a few doubts about the recipricating SU running flat out all the time.
I would suggest you go get that peirburge pump. This is a roller vane pump, just line the main pump, however it has larger (and fewer) vanes so it suctions better.
The reason why the feeder has to run continously is that the petrol in the swirl pot will get quite warm, what with being continiously circulated around the engine. Causing cavitation problems etc as outline above.

To set up a remote swirlpot, you will need to buy
1-a four outlet swirlpot (or weld up in stainless)
2-High pressure pump
3-feeder pump

You might consider a staged approach, because it will not cost you anything to do so and may very well save you some time, effort and expense;
First -Try the volvo filter and pump by themslves, as per Jims suggestion, it obviously works for him.
Second -If that is unsatisfactory then go buy the peirburge feeder pump and a large filter. I use a soup can size ($20) one from K mart.
Third -If still not satisfied then go get a swirlpot, and fit it, using all of the above to run the rest of the system. No money wasted.
What ever you do, let us know how it turns out.
Best of luck.

Bill is "converting" to EFI, so if his original pump can keep a carburetted V8 running, it certainly can keep a swirlpot topped up. It may or may not be an SU. I don't like SU pumps myself, but they are quiet, not like the roller vane types. For what it's worth, I used the original SU for about 8 years to feed a Holley carbed V8. It was eventually replaced with a noisy Red Holley pump. Barrie E
Barrie Egerton

The pump I am using now is one of those "little square noisy" things! I rubber mounted it, and it helps quiet it down some. I was going to replace it with something quieter when it failed. But the damn thing has been on there 20+ years and it just wont die!!

Ed, what year VW Golf, is the pump/tank combo off of?
bill jacobson

Just in case Barries words are misinterpreted and Bill gets the wrong idea (most people have a talent for seizing on the wrong interpretation, I certainly do). I expect B ment that roller vane pumps can be noisy if set up wrong.
The Roller Vane pumps are much quieter than the reciprocating pump, if they are fitted right. My two make a faint hum that can just be heard about one foot away when the engine is running. On a couple of occasions this summer, when the tank was almost empty I could just hear a pump noise from the drivers seat, which reminded me to look at the petrol gauge, just in time
The feeder pump has to run petrol into the bottom of the swirlpot /auxiliary pump and out of the top of it back to the main tank. Pretty well continuously. it can’t just top up, because of the temperature issue, and the accumulation of gas (as in ‘solid-liquid-gas’, not petrol). The initial boiling point of petrol is around 25 degree C after all and they always put a little butane in the mix as well, refineries make more money that way.
As far as topping up goes; one of my early set ups involved a T piece just prior to a large filter and the bosh pump after the filter. The return line from the engine going into one branch of the T and a Japanese reciprocating pump topping up the circuit from the other branch. I foolishly assumed that any petrol in a gaseous state would just go through the motor. This ran for about 10 or 15 minutes until the engine warmed up, the petrol in the circuit warmed up, gas accumulated and stopped the motor. Once the whole thing cooled off it would start again, until it got warm again!. I also tried a variation of two circuits and two T pieces, one on top of the big filter and one on the bottom. A kind of cheap swirl pot. The result was loud buzzing and cavitation (much worst than the bosh pump by itself) as bubbles of gaseous petrol went through the main pump.
Petrol is tricky stuff!

You could try wrapping the square thing in noise insulating foam. The petrol should keep it cool.

Here's another option, build your own surge tank:
Steve Mc

Not my idea. My friend did a restoration on his 65 vette which it had a FI engine (Rochester)which it was brought to todays standards, it looks like the old FI but it's not. After having some problems with the fuel getting hot. He was advice to install a fuel cooler on the return line. The cooler he used is for a transmission. this system uses a low pressure regulator, and it's return to the fule box in the manifold VST

Same can be done by returning the cool fuel to a small tank that also feeds the injectors on the high pressure side.

My friend worked very hard on this project and it's a one of the kind. perhaps the only one. Here is a link to the article that was printed on Vette magazine.

Ken is the author of the article
Bill Guzman

Thats a useful link Steve, some nice photos, I've seen some stainless cooking/cookie tins that might make a good starting point for a swirl pot. You could use brass hose fittings with a nut on the back.
Although, the design would work slightly better if the feed from the main tank went in at the bottom of the swirl pot, rather than the top. That way cooler petrol would be, being fed near where the main pump takes and all the bubbles and vapour would go out the top end back to the main tank. Also the return back to the main tank should go into the bottom of the main petrol tank. Or at least fed into a line that runs down to the bottom, so that most of the light ends will redisolve back into the main (cooler) bulk of the fuel, otherwise there would be alot of vapour going out of the tank. Aside from a small loss of economy, I think your octane number would also change slightly as you used up the tank.

I had a look at a VW golf tank, but this needs to be submerged into a larger tank. I think it is the ideal unit to use if you are having an in tank pump because it comes with its own swirl pot. However, you still need to put in an easily accessed flange, because you've got to be able to replace your fuel pump by the side of the road, if necessary. I carry a spare in the boot as I sometimes can be very far from help.

I'm inclined to think that my two pumps and a filter are the easiest cheapest approach, and have clocked up over 30,000 km, however, the thing about people who cram V8's into MGB's is that they tend to have their own unique take on things which every now and again throws up something new and better. Evolution, I'm a big fan!

Steve, that link is worth looking at if only for people to be able to clearly see the routing of the fuel - easier than trying to understand it from a description.

The filter head version (Tony posted a link above) takes the place of the metal chamber and has the added advantage that you get added filtration and a handy head with mounting brackets - in other words you don't have to fabricate anything.

For a ready made return to the gas tank, see
Bill Spohn

Hi Bill (Spohn)
Your comment earlier about the size of the filter. I am mounting the filter/surge tank set up in the trunk on the bulkhead. I purchased mine from Bronco boys and you are correct about the size of the filter, it would be great if you know of a "shorter" one that could be used?
Tony Bates

I'm in the process of using a swirl pot/pump combo off of a 94 VW Jetta. It's an in tank unit, about 6.5 inches high and 4.5 inches in diameter. Fits into the forward half of the tank without a problem. No need to cut the trunk floor. Unfortunately, things are progressing very slowly because of work and family obligations so it will be a couple of weeks before it is ready to put into the car. I believe it's going to work very well. You can see a couple of pics at the links below. I can go into more detail if anyone is interested.

-- Scott
Scott Costanzo

Tony - the supplied filter with the Bronco unit was a Napa 3281, equivalent to a Wix 33281. It is 6.6" high.

I researched it and found one that had the same gasket size, diameter etc., but was only 5.18" high. It is a Wix 33343 that is used on a Nissan truck of some sort.

Mine is mounted in the driver side battery space and dragging on the ground was definitely a bad idea. The shorter filter tucks everything up nicely.

Hope that helps.
Bill Spohn

Hi Bill,
Perfect, thanks.
Tony Bates

Here is another option as well. Draw back is it looks like the trunk floor would have to be modified for fuel line clearence. They claim no welding required.
Not sure if the baffle/swirl pot would be deep enough for hard cornering. Looks like it would be easy to make it deeper though.
bill jacobson

This thread was discussed between 28/03/2007 and 07/04/2007

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