surge tank location s4 rx7
 

where a good spot to put a surge tank in a s4 rx7 im also going to run a 500hp external pump with it. anyone got any idea's or pics

thanx
madaz

Are you going to do sanctioned racing with it?
If you do, there are strict rules about running your fuel system inside the vehicle.


-Ted

its just going to be for the street and some 1/4 mile work just looking for the best place to put it and a way to get around that fuel smell ya get with it??

If you run on an NHRA track, their rules are sealed baffle with minimum 0.040" aluminum (or equivalent) for ANY fuel components running inside the "cockpit".

If done correctly, you're not supposed to smell ANY gasoline inside the vehicle.  Gas smell inside the vehicle means fuel leak!


-Ted

do you know any spots to mount it???

Okay, retarded question of the week:

How do you plumb a surge tank in the fuel system?

you have a big tank and a surge tank.... a smaller fuel pump feeds the surge tank from the big tank. The surge tank has an overflow tube that replaces the return line and goes back to the big tank... the bottom of the surge tank has a line going out to a much bigger fuel pump, which is capable of feeding high amounts of fuel to the rails. The return line goes back into the surge tank.

I believe that I've seen people mount them under the car as well. You don't have to mount the surge tank in the car if you don't want to. Someone correct me if I'm wrong here.

Zach

Convert to a single exhaust and install the surge tank in place of the 2nd muffler.

and if someone hits you in the rear???? BOOOOOM

Here's a pic of the surge tank on my car. It's roughly 3" round and 18" deep.

-Destin

Because the stock fuel tank isn't located in the rear, right?

Think about it a little... :) The stock tank is protected a little by the spare tire well, so if you feel uncomfortable with the surge tank (a relatively small tank compared to the large main tank) located right at the rear bumper, you can install a few inches of foam between it and the bumper. Just like the stock tank is set up. Clearly, if you are using this setup, you're not going to want to pick a surge tank that would fill all the available space. You need a few inches on each side (and probably 5-6" at the back) of buffer space. The stock main fuel tank is set up in the same way.

Also, it is amazingly difficult to ignite fuel during a collision. Not saying that it's impossible, but I would be quite a bit more worried about the 60 litres of fuel in the main tank then the few liters of fuel in the surge tank if the collision was severe enough to rupture a tank.

I am thinking I am going to put my surge tank where the stock fuel filter goes (under the brake booster) and mount my external pump and filter on the frame rail in front of it (and below it).

I won't have to find a place under or in the car and fuel line routing is EASY as you can use the stock lines for fuel in and out of the surge tank and short funs of the big AN stuff to the pump and from the regulator. Wiring the pump is easy here too as it is right near the + term and I might just use those unused stock EFI relays.

What problems do you guys see with this?

I think it is further from the hot exhaust than anywhere under the car I could fit it and less chance of fuel in the cabin than if it were in there.

Convert to a single exhaust and install the surge tank in place of the 2nd muffler.

:) That is where I had my alum battery box when I had a single exhaust system. Now it is in the dr. side storage bin- it is dry cell type anyways...

I don't think it will fit. There's hardly any space near the fuel filter. Well, it might fit, but it will be tight. Running hose and fittings could be a pain.

So if I wanted to build up a surge tank for my car then I could stay with my Walbro 255lph pump in the main tank and then run a stronger fuel pump in between the surge tank and my fuel rail. Am I on the right track here? It sounds like that would be cheaper in the long run than buying a custom dual Walbro 255lph in tank setup. Especially since I can do all of the metal work myself.

Zach

Generally you want a high volume low pressure pump to feed the surge tank. Since part of the purpose of the surge tank is to keep air bubbles out of the high pressure side, you don't want a high pressure pump churning it up.

Then what size pump are you talking about for the main tank? I just mentioned the Walbro since I already have it installed. Thanks for the advice/info Aaron, it is greatly appreciated.

Zach

The Walbro is a 255LPH pump as I recall, so you need one that will flow slightly more then that. It should be a low pressure type pump.

Any suggestions? I was thinking along the lines of using the Walbro 255 pump in the main tank and then something along the lines of an Aeromotive A1000 after the surge tank. I only know flow rates, I don't know anything about a low pressure pump so any info would help me out quite a bit.

Zach

I don't think it will fit. There's hardly any space near the fuel filter. Well, it might fit, but it will be tight. Running hose and fittings could be a pain.

From what I measured I can fit a 4" dia 10" long surge tank there with no problems.

Any suggestions? I was thinking along the lines of using the Walbro 255 pump in the main tank and then something along the lines of an Aeromotive A1000 after the surge tank. I only know flow rates, I don't know anything about a low pressure pump so any info would help me out quite a bit.

This is exactly the same parts I am working with. Walbro in tank, A1000 pump and its filter.

Once the fuel pressure is off the intank pump it can flow obscene amounts of fuel to supply the 2ndary pump that has to deal with the flow at fuel rail pressures.

According to my calculations... that surge tank would only be a little over a half gallon.... arent they supposed to be a little bigger?

I don't know why it would need to be bigger.

As far as I understand it the surge tank funtions as a reserve of fuel for the 2ndary pump when the primary in tank pump is starved for fuel at its pick up- such as during high G corner.

If you are getting 5 MPG at wide open throttle that would last for 2.5 miles of NO fuel being picked up at the tank wouldn't it? That is a long strange shaped corner to be able to keep the Gs up and still apex it.

Hmm, lapping a skidpad too many times consecutively has caused cars to lose oil at the pan pick up and fuel at the tank pick up so this might do it. There is no way you would be anywhere near wide open on a skidpad so maybe 16mpg or 8 miles of skidpad before there are problems?

I dunno, but I would be more worried about my oil pump pick up or passing out from dizziness and wrecking :P

The intank pump before the surge tank doesn't have to be as big as the inline pump after the surge tank. You plumb the return from the engine back into the surge tank and then an out from there back to the main tank. Also most surge tanks aern't more than 2 liters or so.

-Destin

So from what everyone is saying the my combo of a Walbro 255lph in tank pump with an Aeromotive A1000 after the surge tank would work just fine? I do think that this will be a better solution for me instead of running a custom dual pump in tank setup.

Zach

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

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

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

Zach

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

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

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

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.

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.

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

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

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.

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

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

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

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

-Destin

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. :D

Zach

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

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. :)

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?

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

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. :)

Same as sillbeer's design...

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


-Ted

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. :D

Zach

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

^ 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.

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