1L Swirl Pot Fuel Surge Set-Up Not Working

[SweetBadger 91]

We had a 1hr race at Silverstone on Sunday, and I knew we'd be pushing it with the amount of fuel we'd use so I fitted a 1l swirl pot and an external pump.

The swirl pot was a top-mounted version of this one: http://www.ebay.co.uk/itm/231565599943

And the fuel pump is this one here: http://www.ebay.co.uk/itm/160822629333?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Pic of the setup installed (have neatened up the pipe runs since):



Swirl pot is installed under the boot floor.

 

- Top pipe is return to tank

- 2nd pipe down is feed from tank

- 3rd pipe down is return from fuel rail

- bottom pipe is feed to external fuel pump

I got fuel surge on my last lap before the driver change over (30 mins into the race), so on approximately 1/2 a tank. Then my team mate really had a frustrating 30 mins of racing as it progressively got worse.

 

It's not much, if at all better than when we didn't have a swirl pot at all!

 

Would moving to a 1.5l pot help matters, or is there something wrong with my set-up ?

 

Silverstone does have a lot of fast sustained g corners back to back, but even so I would have thought it would take a lot of time with the tank pump sucking up air before a 1l pot would empty!?

Edited June 15, 2015 by SweetBadger

[Tom Fenton 1,525]

I don't like the pump being potentially above the level of the fuel. I know difficult with where the swirl pot is located but the pump needs to be below the bottom of the swirl pot for me.

[welshpug 1,622]

what are you feeding it with?

[SweetBadger 91]

I also think ideally the pump should be below the level of the swirl pot outlet, but I would hope the draw from the pump would pull the fuel through regardless.

 

It's being fed with a Walbro 255 in tank pump in the standard fuel pump position.

 

I'm really surprised it made so little difference, and quite relieved that 30 minutes of pretty bad fuel surge didn't damage the engine!

[Tom Fenton 1,525]

Roller vane pumps do not "draw". They need a head of fuel to the inlet. I would try moving the pump first of all anyway.

[SweetBadger 91]

Oh right - well that would render the swirl pot fairly useless then as the feed from the main tank is below the pump pick-up!

 

I think lowering the pump using a bit of threaded bar could be an easy fix in that case.

[camgti 56]

The standard pump should be fine to lift the fuel to the swirl pot. So you could also try that!

 

Cam

[SweetBadger 91]

The standard fuel pump was on its last legs hence the replacement, but I think the walbro should be fine for the job of lifting fuel from the main tank to the swirl pot.

[petert 550]

Same thoughts here, very few pumps can "suck". They need gravity to "push" the fuel into the gears/rotors. Without any "head" they'll starve.

[SweetBadger 91]

I guess one quick way to find out whether the pump is getting starved would be to unplug the main tank pump electrical feed so that the swirl pot has no fuel supply and then see how much fuel the inline pump is able to pump out of the swirl pot via the fuel rail?

 

i.e. remove the return pipe from the fuel rail to the swirl pot and leave the inline pump running until it stops moving fuel.

 

Looking at the set-up I also think the swirl pot should be rotated so the outlets face the front of the car - that way the fuel will move towards the front of the pot under heavy braking.

[allanallen 528 2 Cars]

The fuel should be swirling in the pot, the idea is that swirling fuel is unaffected by cornering/braking/acceleration forces, moving the inlets should have no effect.

 

Have you had a look what the return from the pot to the tank is actually doing when the cars running? Ie, put the return into a bucket and run the lift pump. You need to check the pots filling and returning properly so you can firstly rule that out.

[SweetBadger 91]

Hmm, ok that makes sense (and less work for me!), although one thing I'm not too sure about is the design of the pot and where the inlets are positioned - they're only about 1/2 an inch off centre; would this induce enough swirl in the fuel?

 

I'll check the supply to the pot first, I'd certainly hope that it's getting a good supply but I guess the Walbro pump might not like working at low pressure?

[welshpug 1,622]

the idea isnt to create swirl in the pot ! its to avoid the fuel swirling around and evading being sucked up by the pump, hence creating a smaller reservoir of fuel being constantly replenished by the lift pump.

[SweetBadger 91]

I thought in addition to creating a smaller reservoir so that the fuel has less chance of moving away from the pump pick-up, the idea is also to create a vortex which has the effect of de-aerating the fuel so there are no air bubbles in it, and I guess this would preventing it from sloshing around as much too?

[allanallen 528 2 Cars]

That's what I was taught, it's certainly not something I've made up. the inlets are positioned like they are to promote swirling and separate any air. If you didn't want the fuel to swirl the inlets would not go in like they do and you'd baffle them.

What your describing is a sump and not swirl pot.

[SweetBadger 91]

Which brings me back to the question about the design of the pot and where the inlets are positioned. Are they off centre enough to promote a good swirl/vortex?

[Tom Fenton 1,525]

Is all this not a bit academic though? Surely the first step is to move the pump then see what happens? I don't think you'll recreate the fault with the car at rest either, pumping fuel to an open end.

[allanallen 528 2 Cars]

Yep, no need to get hung up on the swirlyness, or whatever other rubbish I've apparently dreamt. That pot should be full pretty much all the time, you'd need a hell of a corner to consume a full litre.

Get the pump where it should be and check the pots filling and returning properly to the tank properly.

[camgti 56]

Try the standard pump first. Im sure it will solve your issues. That how I had mine which was very similar to yours. If its not that then move the pump like suggested above.

 

A proper swirl pot will swirl the fuel by the position if the inlet line. Ie, if you pour a beer into a glass on the side it will creat a swirl!

 

Once the car is on, the lift (standard position pump) pump fills the swirl pot, the larger higher flow pump then takes over.

 

It should be full all the time (or there abouts) as the exterior pump pumping the fuel to the rail will be pretty high flow. You would think it would empty the swirl pot as it pumps more fuel than the lift pump. But, whatever the engine does not need flows back into the pot in the return line from the rail and at the same direction to keep it swirling (and getting rid of air) and once the swirl pot is overfull it then flows back to the big tank. And happens all again.

 

It should be easy to throw the old pump back in.

[petert 550]

I can do a lap of Wakefield on 600mL, or lap of Eastern Creek North on 1L, feeding 250hp.

[SweetBadger 91]

Ha! Yes it'd take a pretty long corner to empty the whole pot!

 

In fact seeing as I'm running a wet sumped 1.9 MI, I'd imagine the engine would expire from oil surge way before the pot was empty!

 

Fitting the standard pump back in is not an option as it was not sounding very healthy (reason I replaced it), but the Walbro pump should be very similar in operation to the standard pump anyway as it's a high pressure EFI pump. Will soon find out if its not pumping fuel to the pot properly by removing the return pipe to the main tank to see the flow rate of the fuel returning.

[SweetBadger 91]

Right then, I've run the lift pump with the fuel return from the swirl pump off and there's plenty of fuel.

 

I emptied the swirl pot and it took approx 10 seconds for the lift pump to fill it, so no issues there - that's probably pumping 8-10 times more fuel than is used.

 

The only thing I'm concerned about is that when I pulled the feed to the external pump off to empty the swirl pot, the pot was very slow to empty. The fuel return line to the main tank didn't allow any air to flow back into the swirl pot as the fuel in the line effectively air locked it... The fuel return pipe runs up hill to the fuel tank so I guess the fuel in the return line creates a U-bend effect and prevents air getting into the swirl pot when it is being emptied. As soon as I pulled the return pipe off the pot, it allowed air in and it drained very quickly. Whether this causes any issues in practice I don't know as I'm sure the swirl pot won't be emptied that quickly.

 

Anyway here's swirl pot mk-ii

 

 

The pump is mounted on a couple of nylon rods (not candles) to lower it.

 

The next race is another 1 hr race at Snetterton, unfortunately the first time we're going to be able to test it is in qualifying - what do you reckon will it sort the fuel surge issues?

[camgti 56]

Sounds right. It will be lock by the line as the fuel in the line is air locked from the inlet side. Thats normal. When the pump is active it should be pushing all the fuel back no sweat.

 

Maybe test that the return line is not blocked from the rail by blowing air through it from the rail back to the tank for peace of mind.

 

Also make sure the tank vent is working.

 

The pot should always be full and the overflowing fuel from the pot should be being pumped back to the main tank via the swirl of course from the external pump.

 

http://img22.imageshack.us/img22/8876/swirlpotdiagram.jpg

Edited June 26, 2015 by camgti

[johniban 59 1 Cars]

Where do you get these underslung fuel swirl pots? id been looking for one for mine as i don't want one inside the car

[welshpug 1,622]

http://www.ebay.co.uk/itm/AN-6-6AN-AN-8-8AN-JIC-1-5-Litre-Aluminium-Top-Mounted-Fuel-Swirl-Pot-Tank-/360958408005