Reply With QuoteGreat artical, I have been wondering about the correct way to do this, thanks
Swirl pots, how to and how not to
Since the carby thing went down well, I reckon I might write a a few more short articles on some things that I see people so often get wrong, and are so easy to get right in various parts of their car.
Swirl pots are a good one, as in some EFI cars we use them for the fuel system and other cars use them for the water system as well. I've seen some horrors out there that would do little except give some more fuel capacity and not function as a swirl pot properly, so here's how to do it.
Water and fuel swirl pots both are built to remove air from the system. The fuel swirl pot, however, also functions to keep the hot(ter) fuel returning from the engine from mixing with the cool(er) fuel that comes from the fuel tank. On the typical stock fuel system the mixing of fuel typically isn't a problem, and you really can't do much about it anyway.
This is how most people at home build their swirl pots, and also a lot (FAR too many!) shops make and sell them.
You've all seen them like that, and they often have a lot more pipes hanging out the side.
And they're all rubbish.
To get the air out of the system, the fluid in it must swirl, hence the name of the gadget. By simply putting the in & out pipes straight into the side, all you do is make a lot of useless turbulence. I guess most of you guys watch Mythbusters ... well a week or so ago they made that large water tank with the vortex in it? That's what you have to do to get the vortex action happening, and by doing that all the air in the system goes to the centre of the pot and can be bled off very effectively.
So here is a good lookin' water swirl pot ->
You can see clearly how the inlet & outlet pipes come in at a tangent to the large pot, thus inducing good swirl. And then at the top there's a bleed line to get rid of all the air. That line can be replaced by the radiator cap, if so required, and it works just the same way.
A fuel swirl pot is a tiny bit more complex, as they have an additional couple of lines going in & out.
Here's a pretty good one ->
It's not perfect though, as although the top two pipe are just right, the bottom two aren't - for the purposes of pumping the fuel from the low-pressure pump from the fuel tank, the tangential pipe into the swirl tank should be at the bottom. The return line from the engine (the tangential pipe at the top) should have a lot of distance from the low-pressure one so as to help avoid the mixing of hot & cold fuel as much as possible. Since the actual vortex of fuel in the pot is not all that chaotic, it works quite well.
The bottom of that swirl pot should also be somewhat dished or angled to a point so the high-pressure pump that feeds the injectors can suck every last bit out of the pot.
By using this system, you can really drain every last bit of fuel out of the main tank and pretty much every drop out of the swirl pot before the engine runs out of fuel. And it also must be mounted vertically.
Making a good swirl pot is harder than making a half-arsed one, but it's worth the effort. To make the dished/angled end caps you can cut a circle of alloy and bash them into shape on a bag of sand, for example. The tangential pipes are harder, but can be done with drills and a bit of massaging with round files.
Attached is an old diagram I drew up years ago that I drew-up for a guy, I just remembered it when typing this out.
#1 is the low-pressure pump feed from the fuel tank to the pot.
#2 is the feed to the high-pressure pump.
#3 is the return from the fuel rail.
#4 is the return to the fuel tank.
HTH!
Re: Swirl pots, how to and how not to
Great artical, I have been wondering about the correct way to do this, thanks
Re: Swirl pots, how to and how not to
there ya go ... there not just bling bling after all.
props to you Bill.
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Re: Swirl pots, how to and how not to
i wouldnt have though that hot fuel and cold fuel makes a difference??? not to certain extremes anyway, i mean the fuel doesnt spend that long in the engine bay anyway and will cool itself to some extent on the journey back to the tank.
Re: Swirl pots, how to and how not to
It gets pretty hot depending on the return percentage and wether cross flow engine, how close to the exhaust and if its going back to the surge tank or fuel tank etc, etc. If racing and you are chasing every last HP cuel coolers help.Originally Posted by millsi
On race engine, drysump tanks to do the job right need to swirl the oil in, to get rid of air and stop foaming.
In the water system it does the same thing along with head bleeds.
Re: Swirl pots, how to and how not to
good point but to most poeple running street can see it making precisly bugger all difference.
Re: Swirl pots, how to and how not to
thats exactly right and why i put the "If racing and you are chasing every last HP, sure coolers help."
Last edited by kingmick; 28-11-2006 at 08:12 AM.
Re: Swirl pots, how to and how not to
perhaps it would be prudent to install a fuel temperature sender in the fuel flow, and then add that to the enrichments for fuel pulsewidth.
the change in fuel temp, vs it's energy of vapourisation, would be relatively small, and so i am imagining that it is the change in fuel density that affects a racing engine more...
fuel cooling was used for F1? etc? in the refueling station, to get more fuel physically in the tank, as opposed to any power gains....
what fuel pressures do F1 cars run? do they run fuel coolers? anything more fancy than a simple oil-cooler type setup?
"I'm a Teaspoon, not a mechanic"
"There is hardly anything in the world that a man can not make a little worse and sell a little cheaper" - John Ruskin (1819 - 1900)
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Re: Swirl pots, how to and how not to
A small part of my point though not quite right.
My main point was how to build them properly, as it's not much harder to do and the fuel system will work better for it, in terms of helping keep the fuel cool and getting every last bit out of the tank.
Re: Swirl pots, how to and how not to
fair call ill shut up now.
Re: Swirl pots, how to and how not to
I thought the main reason for a swirl pot was to insure the fuel injection pump always received a supply of fuel as g forces force fuel away from the pick up in the main tank.If the fuel supply to the pot is interupted for a short time there is sufficient fuel in the pot to supply the injection pump until the low pressure pump can supply fuel again and fill the pot.
Re: Swirl pots, how to and how not to
that would be a surge tank your reffering too.
but at the same time i guess you could combine the 2 if designed properly...
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Re: Swirl pots, how to and how not to
Yeah, that's what it does. Plus some other good stuff if it's built right.
Re: Swirl pots, how to and how not to
Have you ever considered writing a book Bill?
I used to eat alot of natural foods. That was until I learned that most people died of natural causes.
Re: Swirl pots, how to and how not to
Have you ever considered writing a book Bill?
Yeah, though it'd be much along the lines of FMH magazine.
Boobies FTW!
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