MrDirt

You just have to make sure that your return line from the surge tank to the main tank is large enough so that you have a zero pressure system. If it builds up too much pressure, then the surge tank might put some resistence against the return line coming from the FPR. I dont know if that would be terrible, but you would certainly want to keep it to a minimum

RETed

Easily done - use a bigger hose from surge tank to main gas tank versus the return line from the FPR / fuel rails / fuel injectors.


-Ted

BoostedRex

Thanks for the info guys. If anyone else has any input please add it!!

Zach

sillbeer

Not sure what the pressure of the walbro is but wouldn't it be to high of pressure for the supply to the surge tank?

-Destin

Aaron Cake

iTrader: (1)

I just ran into this link on how to build a surge tank:

http://www.sdsefi.com/techsurge.htm

BLUE TII

iTrader: (9)

A pump does not put out any pressure unless a restriction (such as the fuel pressure regulator) is put on its output.

In a properly routed surge tank system there is no pressure (restriction to flow) on the in tank pump.

NZConvertible

There will always be a small amount of pressure because of the restriction caused by the lines themselves.

The best way to do this is to not have the return from the FPR go to the surge tank. Ideally it should go back to the fuel tank. Fuel returning from the engine will be hot, and if that fuel goes back to the tank some of it will again be pumped to the engine. The end result is higher fuel temps at the engine, which is bad for power and lowers resistance to detonation. The downside is having to fit another return fitting at the tank.

sillbeer

The reason for having it plumbed back into the surge tank is to keep it full. Also you can put a fuel cooler between the surge tank and the rail under the car somewhere to keep the temps down. Or just buy the moroso cool can and mount it in the engine bay.

-Destin

BoostedRex

So what is the "correct" way to route the return line? Is it back into the surge tank or into the main fuel tank?

Zach

NZConvertible

No, the pump in the tank does that. If it doesn't, it's not big enough.

That seems like a lot more time, money and hassle than adding another return connection at the tank.

BoostedRex

NZ vert, are you talking about running a return line to the surge tank as well as the main tank or just one return line that goes to the main tank?

Zach

sillbeer

Yea. There is suppose to be a return from the engine to the collector tank and a return from the collector tank to the fuel tank. I bet the amount that the fuel was heated would be very minimal. Also it would be cooled by the fuel in the collector. There is going to be alot more fuel in the collector than what is being dumped back in there.

-Destin

BoostedRex

That makes sense. I really do think that this will end up being cheaper than my first choice. Plus it's a better system than a dual in tank setup. So what's the "official" word on how much capacity the surge tank should have?

Zach

sillbeer

Just by doing a google search the largest I came across is a 3 liter unit.

-Destin

BoostedRex

So anywhere from 1.75 liter to a 3 liter would be just fine then? I'm trying to figure out a good "middle of the road" size and then I can have it fabricated. Gotta love having free in house fabrication.

Zach

RETed

You need to figure out how much fuel you're be using "worse case", and then back out the capacity of the surge tank from the differential flow between the two fuel pumps.

It's sounds harder than it really is - it's just tedious math.

This is just a rough calculation and example...

Popular 550 + 1600 fuel injector combo...
Datalog the pulsewidth at WOT, and this will give you "worse case" fuel consumption.
Just as an example, we'll go 70%...
Approximate fuel flow - 1100 + 3200 = 4300 cc / min x 70% = ~3000 cc / min or about 3 liters per minute.

Walbro 255lph in stock gas tank + Aeromotive A1000:
Walbro ~250lph @ 10psi (should flow slightly more)
A1000 ~300lph @ 45psi (slightly underrated)
So we have a differential of about 50lph or ~ one liter per minute.
Thus, if the A1000 is flowing all of it's fuel into the engine, worse case, the surge tank should drop at a rate of 1 liter per minute.
The Walbro is flowing about 4 liters per minute.

In this case, if at 70% pulsewidth, the surge tank will never empty, cause the Walbro outflows the max fuel going into the engine - 4lpm versus 3lpm.

Now, say the engine requirements are bumped to 5 liters per minute...
We now have a differential of 1 liter per minute between the engine fuel requirements versus the Walbro capacity...
Thus, if the surge tank is approximately 2 liters, this will empty out in about 2 minutes.
Now, 2 minutes of WOT is a LONG time!
Unless you're doing Bonneville LSR runs, this much capcity is more than enough for most road race tracks, where WOT runs are typically 10 to 30 seconds max.


-Ted

NZConvertible

I'm saying it's better if the return line from the engine goes to the main tank instead of the surge tank. The surge tank still needs an overflow line to the main tank, so you need to add another return connection at the tank.

That's one way to do it.

You need to think about what's happening at low load. Because the engine is consuming very little fuel, most of the fuel pumped to it is returning to the tank. Stick your hand on the fuel rail of a hot engine and tell me that fuel isn't being heated up. It's difficult to say how much of that returned fuel is pumped back to the engine and how much overflows back to the main tank, but I'd guess it's about half. So if half of that heated fuel goes back to the engine, it will be heated up even further and most of that will return to the surge tank again. This process is continuous and the end result is elevated fuel temp at low load. This isn't me guessing what might happen, it's a known fact. The hotter the fuel is the less energy it contains and the lower it's resistance to detonation. I wouldn't ever put the surge tank in the engine bay either, as was suggested earlier. That would just turn it into a very effective fuel preheater...

It's just something to consider. I'm not saying the other way is wrong, I just think this way is better. It's how I'd do it anyway.

BoostedRex

I think there is some really great tech info in this thread now!! Could a mod possibly clean the thread up a bit and then add it to the archives??

NZ, what you're saying makes sense. I hadn't even thought of that. Plus, it wouldn't be very difficult to add one more return line onto the main tank. Here's the list of bungs that should be welded onto the surge tank if I'm right. Please correct me if I'm wrong though!
1. Bottom of the tank going to the fuel rail
2. Top of the tank for overflow
3. Top of the tank from the main tank

Then the main tank would have
1. from main tank pump to surge tank
2. return from fuel rail
3. return from surge tank overflow

Am I right here?

NZConvertible

Sounds good.

Here's a pic of a brass bulkhead fitting added to the top of a fuel pump mounting plate on a late-model car. I haven't looked that close but the same fitting should fit onto the FC's plate.

http://us1.webpublications.com.au/st...6/2637_5mg.jpg

If you're going to make a surge tank, fit the inlet connection(s) off-centre like in this pic. It causes the fuel to swirl in the tank with reduces aeration (air in the fuel).

http://us1.webpublications.com.au/st...5/1576_2mg.jpg

BoostedRex

So you the surge tank in that picture has two inlets from the main tank correct? Then the hole on the top of the tank is the return to the main tank and the hole down by the mounting brackets is going out to the fuel rail. Am I right with how I'm thinking of all of this? I just want to make sure I get everything right so I don't screw it up on my car.

RETed

Same as sillbeer's design...

http://fc3spro.com/TECH/MODS/FUEL/surge.htm


-Ted

BoostedRex

Thanks for that Ted!! I should've looked over your site for that first. I don't know how I missed it. I think I have most every other part of the site memorized.

Zach

Aaron Cake

iTrader: (1)

I'll archive the thread when it ends...

Falcoms

^ Thanks aaron and everyone who added info to this thread! Really did explain it to me and hopefully others learned alot as well. Unfortunatley, with the way that the stock fuel system is set up, the car under hard cornering to the left will drop fuel flow, which will make this a fairly viable option for more than just myself, I hope.

BoostedRex

Yeah, after pricing out everything needed for this system it just doesn't make sense to me not to run it. Thanks again to everyone that contributed to this thread. Especially RETed and NZConvertible!! Thanks for archiving this Aaron.

Zach