A better track fuel pump setup
 

The fuel pump setup I have been running with has not worked as well as I had hoped (see details below). I could not consistently pump the tank dry which meant I never knew exactly how much fuel was in the car, and it would still starve at around 2 -3 gallons (I think).

My goal is to cross the finish line just before I run out of fuel. This way I am carrying the least weight possible. I don't like to rely on fuel for ballast so the car meets minimum weight bone dry. Not being able to consistently empty the tank makes fuel calculations difficult. I was bumped from P2 to last recently due to a fueling error (was 4 pounds under weight).

This is a diagram of my original setup detailed in my build thread. I used a Series I pump on each side of the tank as lift pumps to my surge tank in the trunk, which has its own pump feeding the fuel rails. I ran return lines to both pump bowls so the pumps would not starve and overheat. Problems with this system were that there were a lot of aftermarket fittings which increase cost and points of failure, connecting the -6 AN fittings to the pump assemblies was problematic in that my initial method resulted in kinking of the feed hose when the assemblies were installed, and as above, I could never be sure the tank was empty. I tried various modifications of this setup with minimal improvement.

Attachment 286056


Below is what I've been happiest with. The tank has the stock Series II pump assembly and siphon, pumping returnless to the surge tank. The siphon relies on regulator blow-by to work so If I was to run a return line from the surge tank to the fuel tank the siphon would not work. The surge tank then pumps to the rails. This setup can result in air being trapped in the surge tank so I have a vent line running to the emissions vent fitting on the fuel filler neck (easy to do). I placed a flow restrictor in the line (0.0010" orifice) so that air can purge but very little fuel will leave (actually it's about 100 ml/min) and what does just flows into the left side of the tank via the filler neck. With this setup I can pump the tank dry and run down to 1/2 gallon before I get fuel starvation.

It would be nice to modify the OEM regulator to a lower pressure (maybe 30 PSI) but for now I'm sticking with this setup.

Attachment 286057

I've also discovered that Vibrant makes an adapter for OEM fuel fitting to -6AN fitting. Pump is 3/8", rails are 5/16". This makes running AN lines so much easier.

https://vibrantperformance.com/catal...1347_1429_1435

I would recommend changing to a rollover type vent. It will seal when the canister is full, allow venting when needed, and then not potentially leak and catch fire in a rollover scenario. I’m surprised it’s not actually required by your series.

A lot of classes don’t allow a surge tank. Not convinced myself that one is needed, but it is an easy solution though not without some risk as an external setup. IMO one issue with your dual pump setup was in using two S1 pumps. It’s not a good design.

Just pulled my tank the other night and am in the process of doing my own deal. We can’t use sumps and such; either internal or external. It seems to me many people overlooked some things whether single or dual pump, but maybe I’m the one missing the obvious. I’ll find out one way or the other.

Unless I'm not understanding the function of a roll-over valve, I don't think it will work. I need to vent air out of the surge tank so it will fill completely, not into it. All the roll-over valves I'm familiar with allow air in and out unless inverted. Since my surge tank in pressurized from the main fuel tank pump, fuel would exit the valve too.

The surge tank is a closed system other than the pin-hole vent.

Am I misunderstanding? I'd love to find a valve that flows air but not fuel.

Here’s one supplier, pretty sure there are others

You Tube

So wait a minute, I don’t see a line from the surge tank back to the fuel tank, just the line from the fuel tank pump feeding fuel to it. I’m going to assume you forgot to show that.

If you were to lower the tank pump pressure it would probably require redesigning the siphon setup. Because the OE setup might not have enough pull without it or draw too slowly. Which Radium sells a siphon setup for that purpose. Or you might try pulling the tank fuel pump speed control relay out. This forces the tank pump to always run in low speed mode, but again I’m not sure what the result is on the siphon draw.

Here’s the test I had run on the S2 pump in low speed mode (10Volts). It cuts flow about 1/3, but is still fine for your purpose.


https://cimg9.ibsrv.net/gimg/www.rx8...b489258b6.jpeg


An external regulator between the tank pump and the surge tank feeding back to the fuel tank Is another way to address it. While it allows the OE pump to duplicate the original operating conditions, it also adds complexity, cost, and so on. Ultimately when you’re using the OE fuel module though the design limitations of what it was originally intended to do are going to define the end result.

After additional thought I think you don’t have this configured properly; the surge tank should be closed-loop plumbed back to the OE tank. All you should be doing is pumping fuel to the surge tank with the excess returning back to the fuel tank. The OE fuel tank is vented, has rollover valves, etc. The surge tank pump should be pumping to the fuel rail, but it needs a regulator with the bypass coming back to the tank or pump module basket. Since I can’t run a surge tank I didn’t put much thought into it.

I’m actually confused by your diagram. You either have it drawn incorrectly or it’s not plumbed properly if that is the true representation. The surge tank should not be pressurized. Your drawing seems to indicate it is and there’s no relief or bypass on the fuel rail supply line. I’m assuming you don’t have the surge tank pump setup on a fuel pressure vs fuel pump pulse width control scheme.

Here is dual pump kit , Some shop in Japan develop for Rx8, I think this is more for streetcar and semi bolt on solution

Side note there is no place in tank to try holly hydramat ?

I'm confused as well.. the surge tank has to be pressurized if it is plumbed that way. I assume both in tank pumps are using the built in regulators to deliver the correct fuel pressure?? There isn't much of an advantage doing it that way as you are still limited by the tank pump pressure and fuel delivery.... and if one is running dry it will likely back into the other because as far as I know there is no check valve on the pump. The reason you use low pressure pumps out of the tank is because the stock pumps can flow lots at low pressure.... and then you use the surge tank pump for pressure.

Where is the regulator for the high pressure pump? Return type fuel system to engine? Or returnless??

Dannobre and Team are correct. The way you have this plumbed will not work well, if it works at all.

I recommend using a Radium surge tank that has an adjustable internal bypass regulator and high pressure pump:

http://www.radiumauto.com/Assets/Pro...d_pic-4241.jpg

Combined with a stock S2 fuel pickup assembly modified to add a return port to dump excess fuel from the surge tank into the fuel basket in the tank, this should do what you want. The stock in-tank pump will function fine as a lift pump for the surge tank since it will be operating with very little head pressure, and the regulator on the surge tank can be set to the stock fuel pressure setpoint. This will allow you to use the stock fuel rails. Because there will be a constant flow of fuel through the stock in-tank pump, the siphon should work correctly.

Add a relay that switches on when the in-tank pump switches on, with its own dedicated fused line to the battery, to provide power to the pump inside the surge tank.

If you really want to get every last bit of fuel out of the tank, consider picking up the Hydramat that mates to a stock S2 pump and cutting the bottom out of the S2 fuel pump assembly so the Hydramat is flush with the bottom of the fuel tank.

First, sincere thanks to all of you for your thoughts and input on this. I am prepping this car for SCCA Runoffs this year and need it to be right.

John,

That is the Radium tank I am using. It is a returnless setup from Radium.

The diagram is correct. I am running the surge tank pressurized to the stock fuel pump pressure. I spoke with the Radium techs about this and they didn't exactly understand the logic but did not see a functional problem with it.

It was my understanding (from reading this forum) that the siphon venturi is fed by the regulator bypass flow, not the actual fuel flow to the rails (or surge tank in my case). If I use the OEM pump as a lift pump the siphon doesn't work if the above is correct. That is what I was doing in the first configuration.

Yes, the Radium pump has little head pressure but I couldn't find that being an issue anywhere.

So what are the risks or disadvantages of running this system as shown. Both pumps are running returnless as designed.

AC

I wasn’t aware of them having a returnless surge tank setup.

http://www.radiumauto.com/Blog/Post/...rts-in-one--83

The surge tank vent line should return back to the OE fuel tank regardless.

it seems to me that you’re compounding the 2nd pump with the first. Do you have an actual fuel line/rail pressure indicator? If it were me, I’d put a restrictor between the two to drop the pressure to the surge, but still have the OE tank pump operate as intended. Also probably would pull the speed control relay to slow it down.

The other issue I see is that by not flowing through the surge tank with the tank pump is during low flow situations, such as idle, the surge tank is in high bypass mode with only that small volume of fuel within itself. Which I’m assuming you don’t have a second speed control relay on it like the OE pump. That has potential to overheat if you leave the car idling for a long time. By backpressuring the OE tank pump to not pressurize the surge tank and keep it functioning as mentioned above, but then allowing the excess flow go back to the OE tank would help to minimize that potential issue.

Interesting. I have my in-tank pressure regulator bypassed with a plug and my siphon seems to work correctly. I do have a Radium Jet Pump I intend to install to increase the siphon flow.

Again I agree with Mark, the return from the surge tank should go to the factory fuel tank. I suppose discharging it into the fuel filler neck would work, but that just seems strange to me.

Well I misinterpreted that it was feeding back into the tank through the filler neck. That’s essentially the same as going back to the tank even if taking the long way there, but per my previous post imo the restrictor needs to be moved to the feed line and then flow freely from the surge tank.

Thanks guys.

The series 2 fuel pump top is waffled underneath, unlike the the series I which makes plumbing a return line a little more difficult. Not impossible, but more difficult to seal the buckhead fitting. It's easier routing to the filler neck. Otherwise the tank has to be dropped. The restrictor is in the return line because I do not want a lot of fuel flowing that route, only the air that might get trapped in the top of the surge tank.

The OEM pump is hard wired but I do have it powered through the OEM resistor for that reason.

Overheating in the surge tank is a good point. I'll watch for this.

Yes, I have a fuel pressure sensor at the rail, Adaptronic uses it for fuel management.

This is the thread regarding the siphon venturi. The info is for a Series I pump assembly. I do not know if it is the same for Series II. I have a spare one so I may have the information soon.

https://www.rx8club.com/series-i-maj...1/#post3074524

Regardless, first time out this worked better than anything else I've tried.

I'll think through all of this. Thanks.

If you check out my thread in this section I have some pictures of how I accomplished the fuel return to the S2 fuel basket. It was super easy to eliminate the reinforced plastic to add a bulkhead fitting. I've had no issues with leaks.

Sounds like what you have works, so that's great.

Except Capt. Pedantic notes that locating a regulator at the back near the pump makes a lot more sense than to pump it all the way to the engine and then back again. All those energy losses could instead be powering the siphon better with direct, shorter routing.

Sure, if you don't have a pressure reference line to run back there.

Plenty of people run it back there including Radium with that particular surge tank he used :dunno:

Certainly it can be done.

So I did some digging and it turns out that Radium makes a combination in-tank relief-valve/venturi-siphon assembly that they’re using on their in-tank pump conversion kits for certain cars


https://cimg5.ibsrv.net/gimg/www.rx8...08cf4755b.jpeg


Unfortunately after discussing it with them they don’t/won’t sell it separately though. It’s a simple and efficient way of doing it on a NA engine and I was hopeful to get my hands on one, but no go. :(

Why not just use their venturi jet pump? You can use it with the stock regulator I'd think.

On an S2 pump? Not worth it to me. If I could get that combination device I’d block off the OE one and rework the pump discharge to accommodate it as so


https://cimg2.ibsrv.net/gimg/www.rx8...e0e975f48.jpeg



but without it will pursue Plan B instead.

I need to correct my post. It appears that my siphon is not working, or not working very well, with the in-tank regulator bypassed.I tested it Sunday and it's got almost zero suction on the right side of the tank.

I'll be working through the Radium Jet Pump install this week and will take some pictures of what I end up with.

John

Well my apology too because when you mentioned blocking off the bypass valve I failed to recall that doing so blocks off the flow path for the siphon. So that’s why it doesn’t work. As I mentioned to you previously, I still don’t quite get how all the appendages on the small black lines tied into the siphon fully interact together. So those appendages aside, if you look at the diagram I posted in the previous reply, it functions along the same design principle and you can see how blocking the bypass also shuts down the siphon.

Edit: Here’s the S2 RX8 diagram, on the S2 pump module the siphon is before the pressure bypass rather than after. It’s possible that blocking the bypass on it may result in fuel pushing over to the other side.

https://cimg4.ibsrv.net/gimg/www.rx8...c63cefcb64.png

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