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surge tank setup


loner

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The way I see it, there will be flow... but there could be additional pressure to the rails if there is pressure in the surge tank.

I\'m not convinced the pressure in the surge tank will be significant, or that the flow will be slow enough post regulator to cause

an increase in fuel temperature... but I take a look at least.

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 titian']

[quote name='gotasuby said:

How can you have no flow through return if you have a pressure pump which is pumping 300l per hour into the rail and injectors are only using 10 for example? It doesn\'t magically disappear.

/quote]

Back pressure from the tank pump in the surge tank. OK not all surge tanks will have pressure of any note.But if there is any pressure in this surge tank and it is directly joined to the rail return it will impede flow, Not all systems always. :)

Also your rail supply pump does not circulate/pump its full capacity all the time. There is an internal recirculation within the pump itself for cooling. The full flow rate will only be available if the supply is disconnected. Other than that it maintains a flow through the FPR at somewhere around 70% of its maximum output. Unless there is pressure in the return system which will slow the flow even more. (As I understand it that is)

Mine was not flowing well. I therefore researched and found nothing here. So I therefore corrected the flow characteristic of my setup and then also created this "discussion". As my vehicles are all Subaru. ;) ;)

Yes if there is pressure then it will restrict flow but as long as it fuel pressure is what it has set to it won\'t make any difference as it is obviously flowing well enough for system.

Pumps flow less as pressure goes up but are you forgetting that while the surge tank increases pressure then it makes the main pump not work as hard at it already has pressure on it? So you could have 30psi pressure in surge tank and it would be awesome as the main pump would only have to add 13.5psi so would flow more. Only issue from too uch return back pressure would be fpr not big enough to flow thus getting fuel pressure creep

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What I was saying was it doesn\'t matter if you have return back pressure as long as fpr can keep fuel pressure at set level.

For shits and gigs today I decided to test out theory on the rally car. I powered up both pumps. One being Walbro lift pump. Other being 044 Bosch. No motor in car so just joined in to each other return and feed with a fpr in between. Fuel pressure set at 3 bar with standard sti v8 reg. Return pressure was just under 5 psi after reg and surge tank was just over 1 psi. Then I turned off lift pump. Return pressure dropped to 3.5psi and surge nill. Fuel pressure stayed exactly same. Then I powered up again the lift and started to block off the return to tank and monitored both fuel pressure and surge tank pressure. I found that fuel feed pressure stayed exactly 3 bar up until surge tank crossed over 1.5 bar in it then it started to creep up. I think to do with Bosch pump over powering reg. So as long as surge tank stayed below 22psi the fuel feed pressure was perfect.

So there must be something different with your setup?

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Interesting to note that the Bosch 044 and Walbro 255 flow pretty much the same at low pressure ratio\'s. Which means that if you have a Walbro lift pump, flowing into the surge tank with an orifice restriction on the surge tank return maintaining ~10psi or so, the Bosch 044 cannot outflow it (apart from the situation that the surge tank is intended for which is when the lift pump can\'t pump any fuel as it has all sloshed onto the far side of the tank)...

FuelPumpcomparison_graph.jpg

I\'m still trying to find some actual research into what happens to the flow rate in the various situations described. As it is highly dependant on the type of pump used. I suspect that the output will be as Loner and Gotasuby have said where at a certain pressure, the pump will be flowing a set amount as thats the main characteristic that a fuel pump needs to have.

There also could be the scenario where downstream pressure after the regulator could be raising the upstream pressure?

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  • 2 weeks later...

Super interested topic !!

How are u guys checking pressure in surge tank?

Curious as to check mine now

I run my surge tank with the regulator return feeding into sure than surge into fuel tank return for the same reason that I want to make sure surge tank is constantly full

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Aww yea sweet I have a spare port for dual pumps ill just chuck a gauge on there

I\'m a little confused about this whole fuel hanging around etc -

Saying that fuel will linger in the fuel rail ? I don\'t understand how fuel can sit there when the injectors are taking heaps of gas and anything else is forced out the return cos it\'s all flowing - I\'ve never seen water in the middle of a flowing river just sit still and the rest flowing past it

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Lolol u get what I mean tho don\'t u

On wot I highly doubt there\'s any chance that fuel could sit in the fuel rail

On idle / cruise I\'m thinking yea maybe because the injectors aren\'t taking much at all- but the amount of fuel coming into the rail and the fact it has a return line - I don\'t see of understand how some fuel can sit in the fuel rail and some fresh (colder fuel) can go around the hotter fuel and go back to tank ? Lol

Wouldn\'t it just be constantly flowing and constantly having fresh fuel in the rail

Now if we talk about a ls1 or similar which has no fuel return what so ever - than fuck yea fuel would just sit in rail

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I spent a few nights reading around google on various peoples thoughts on surge tank set up\'s. Even Motec (page 21) suggest the usual method of regulator return going to the surge tank then returning to the main tank from there.

There is a lot of discussion around the correct way to plumb that method though as the fuel inside the surge tank should be set up too swirl to keep the cool incoming fuel "separate" from the hot returning fuel and ensures that the hot fuel is also the first to return to the main tank.

The fuel pumps are positive displacement so at any operating pressure, they are flowing the set amount as shown on their pressure vs flow graphs. The overheating of fuel issue arises from the hot fuel being recycled through the pressure pump and back to fuel lines while the cool incoming fuel gets returned back to the main tank due to the surge tanks design and pipe routing. So the design of the surge tank and the routing of the fuel lines has a lot to do with the effectiveness of the setup.

I saw quite a few mentions of putting a slight restriction in the surge tank return to keep it at ~5-10 psi, but this was also mentioned usually with mismatched setups where the intank pump feeding the main pressure pump may not be able to keep up with the main pressure pump under full load. As mentioned earlier, this could be dangerous as all your pressure will be set with say 10psi in the surge tank under normal operating conditions. But if the feed pump can\'t keep up, then right when the main pressure pump is under full load and using all available fuel, the pressure in the surge tank will drop and cause uneven pressure variations in the fuel rail. So in my opinion, it would be safer to have a zero pressure setup that just relies on the amount of fuel in the surge tank to supply the main pressure pump until the feed pump catches up later if your feed pump doesn\'t flow as much as the main pressure pump can.

If the two pumps are correctly sized, and the feed pump has plenty of overhead over the main pressure pump\'s flowrate at peak operating pressure, then the surge tank can be kept at an elevated pressure all the time and the return from the fuel rail can go from the regulator straight back to the main fuel tank and bypass the surge tank. Therefore allowing fresh, cool fuel too always be fed to the fuel lines.

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All this talk of the lift pump being able to keep up etc - on wot u see 60 psi fuel pressure of your running 1 bar and stock fuel pressure - lift pumps only doing 1-10 psi max - the flow is alot more at 1-10 than it is at 60 psi -

I run a stock sr20det lift pump in the tank and a external walbro pump off the surge tank - and I\'ve never had issues and the car lives on wot on te track

The stock pumps rated at like 180 or so lph at 3 bar so it would be over 255 at <1 bar - and the external wouldn\'t be flowing anywhere near 255 at full fuel pressure (can\'t see the graph ATM but it would be alot lower) - would be pretty dam hard to not supply enough flow at such a low pressure

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Generally speaking that\'s true. Considering that your average setup consists of a Walbro as a lift pump and a Bosch 044 as the main pump. And the Walbro has the exact same flowrate at low (0-20 psi-ish) pressure as the Bosch. So when the Bosch is pushing out min 30 psi and up to maximum pressure, and both pumps are running fine, then the Bosch cannot flow more than the Walbro and you could run a return direct to the main fuel tank and not have the fuel overheating worry.

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I don\'t know why people go for a walbro as a lift pump tho ? Because its doing such low fuel pressure u don\'t need that bigger of a pump-

I took my intank walbro out in favour of using the stock pump for that reason and also walbro pumps tend to not last very long picking up air

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Cause there\'s a huge amount of people who go through the natural process of upgrades that involves buying a Walbro as a first step cause everyone says you need one. Then deciding to go to the track and wanting a surge tank for extra protection. So then going for the other most common fuel pump upgrade in the world which is the external Bosch 044.

Perhaps?

From what I\'ve seen, there\'s very few people who set out on their modifying journey with the exact end build planned from the beginning. Most of the time it\'s a case of buy parts as you go and the above also appears to be the most common path that people follow. It\'s only been in the last few years that there has been some proper decent alternatives come readily available as it wasn\'t that long ago that those seemed to be the only fuel pumps on the market.

Plus the Walbro was cheaper than a factory pump which tend to die at the 150k km mark.

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  • 2 weeks later...

Im just going to interrupt and pop a question, Do I need to get a low pressure high flow fuel lift pump to surge tank because I dont seem to be able to find one anywhere. Or can i just buy two walbro pumps and use one as a lift pump and the others as main pump to injectors??

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Well one needs to be an inline pump and one needs to be a in tank pump -

And as per how pressure is created - any fuel pump will work as a low pressure lift pump because the fuel regulator is what makes the pressure - the lift pump simply fills the tank using stock / walbro intank pump works fine

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 loner']

You don\'t need something as capable as a walbro for the in tank pump though... if you can get something that fits, and is cheaper... get that.

correct but as Koom pointed out.. this is a very common path, and that walbros $ < oem $. walbro lifting certainly wont do any harm

[quote name='Koom said:

Cause there\'s a huge amount of people who go through the natural process of upgrades that involves buying a Walbro as a first step cause everyone says you need one. Then deciding to go to the track and wanting a surge tank for extra protection. So then going for the other most common fuel pump upgrade in the world which is the external Bosch 044.

Perhaps?

From what I\'ve seen, there\'s very few people who set out on their modifying journey with the exact end build planned from the beginning. Most of the time it\'s a case of buy parts as you go and the above also appears to be the most common path that people follow. It\'s only been in the last few years that there has been some proper decent alternatives come readily available as it wasn\'t that long ago that those seemed to be the only fuel pumps on the market.

Plus the Walbro was cheaper than a factory pump which tend to die at the 150k km mark.

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