In-Tank Swirl Pot -- Ready to Roll
 

I was driving my '84 a month ago and noticed a stumble when I cornered hard with less than 1/4 tank. My car's a turbo about to be tuned, and I know that fuel starvation is a bad thing while on the boost, so I decided to fix it. I was faced with a bunch of options, but after talking to a lot of people who had dealt with the same problem, I decided on a swirl pot (surge tank). The next problem was where to put it. I looked all around the car and eventually decided that the best place was in the fuel tank so I wouldn't have to cut or futher modify the car. I made a nut plate out of mild steel that I welded into the top of the tank, with a 3" X 6" opening. The swirl pot is 3" dia X 10.2" tall, so it holds about 1 liter. It's set up to induce clockwise swirl. The whole thing is 6061 T6, including the tubing, and it fits nicely inside the tank. The wire is 14 Gauge with Tefzel insulation, so it will resist fuel. I tested the lift pump, and it pulls less than 4 amps. See the pics and diagram below for more info. I'm waiting for the paint on the tank to dry so I can install it and live without stumbles.

BTW -- my old setup was a GSL-SE tank, with the reservoir cup in the bottom.

I must say... that is pretty badass.

Very nicely designed solution for your fuel starvation problem, quite creative. I've seen external surge tanks, but never an in tank one. Where did you come up with the idea?

It was a mixture of current solutions. I initially wanted to use an ATL-style in-cell surge tank with trap doors, but I was warned that those don't work as well as a true surge tank. I then tore apart an OEM fuel pump module and saw how it worked (an ingenious design that does basically the same thing as my setup using only one pump), then I figured I could get the best of both worlds with this design.

I like your solution, but I might be inclined to make the swirl tank larger in order to hold the main supply fuel pump, keeping the other intank pump to fill the swirl tank. Not sure if there's enough room to be accomodate both. Either way, kudos to your ingenuity and quality of the finished solution.

If I'd started from scratch, I might have gone that route, but the rest of the fuel system was already there, packaged, tried, and tested. Also, packaging a second pump would have been very tricky. Lastly, the external -044 is just loud enough that I can hear its health before I start the car, which is kind of reassuring.

very interesting and cool

Umm,i must say : "Holy shit Batman,nice fabrication work there!"

:)

Thanks for the nice comments. I think that under the following conditions, this is the best solution:
- fuel injected, especially turbo
- don't want to cut your car
- don't have room under hood for a swirl tank and pump
- drive around corners fast on a low tank (less than 1/3)

I post this kind of thing for two reasons. First is to "check my math" -- it's nice to hear about anything I might have screwed up. Second is to share ideas with others who might have the same issue.

Since nobody sees any big problems with the setup, it'll go in the car tonight. And, if you plan to do anything similar, feel free to contact me -- I've done a lot of research on this.

With the in tank pump flowing less than the external pump (silly question, brace yourself) wouldn't you run out of gas in the surge tank? I know you have to basically be floored the whole time (or not?).

EDIT: Hey guys, I am an idiot. Disregard this useless post. I am tired :(

No it's a good question -- note that the flow rates are at 5 Bar. The Lift Pump doesn't have to fight against any pressure, so it can flow more than the rating.
The flow is rated at 168 Liters / Hr at 5 Bar, but Bosch doesn’t specify the flow at zero pressure. To be sure, I tested the pump, transferring a 5 gallon bucket of gasoline into my car’s fuel tank. Test perameters were at 85 deg F, 12.0V, with a 3’ round trip run of 14Ga. Wire. The pump emptied the 5 gallons in almost exactly 5 min. = 227 LPH. This slightly exceeds my requirements, and the flow should increase a bit more with the 13.8V in-car voltage.

This exceeds the rating for my Pressure Pump at 5 Bar, but it really flows more than 200 LPH for two reasons: 1) Bosch tests their pumps with Heptane, which gives them a slightly pessimistic flow rating compared to gasoline 2) I'm running an MSD Pump Booster to the Pressure Pump.

To be safe, both pumps must flow fuel equal to the engine's consumption at max HP. The pressure pump must do it at base fuel pressure + max boost, while the lift pump must do it at free flow.

I set max HP at 500 (flywheel), which is approximately what I made on the dyno (430 RWHP).

HP X BSFC = Fuel Consumption
(500 HP) (.70 Lb/HP-Hr) = 350 Lb/Hr
Gasoline density = 1.621 L/Lb
Fuel consumption = 216 L/Hr

I know the pressure pump can keep up because the pressure held rock steady while on the dyno at max HP. I'm pretty confident the Lift Pump can keep up too, since I had an 11 LPH safety margin, even at the lower voltage.

The other factor not figured in your flow rate calcs is the unused fuel from the return line empties into the swirl pot, which adds to what the intank pump pumps. I see no problem in the differential between the 2 pumps output. The swirl pot should remain full at all times until the fuel tank get so low that the intank pump can't pick up ay fuel.

You're correct. I assumed a worst case situation where the engine used all the fuel the pressure pump could supply. In the real world, there will be some return fuel which will, as you say, help keep the swirl pot full.

Looks like a great solution.

Heres a question and great job testing your results.

Whats the fuel temp difference between in-tank and the return line?
is the return line fuel at a higher temperature than the fuel thats already in the tank?


Can't wait to see what this 1st gen looks like finished.
-Ben Martin

I'm sure the temp will be higher. Any time you stir a liquid it heats up, and with 200+ LPH running through the system at high pressure and light throttle, I'm sure I'll be doing a nice job of warming the gas. The highest temps would be seen in the swirl pot itself, since that's where the big boy pump dumps its excess load (and heat). The swirl pot is, however, aluminum, and it will use the rest of the fuel in the tank as a heat sink.

In an out-of-tank swirl pot, a trick some use is to put a 5 PSI bypass-style FPR on the overflow that returns to the fuel tank. This will maintain enough positive pressure in the swirl pot that it will prevent cavitation in the pressure pump, even when the fuel temps rise. I had a FPR go bad on me once, so I didn't do this, since I figured the heat sink effect would keep me in the safe zone. What I did do was make the orifice for the return line fairly small (3/16") so it will create some small positive pressure inside the swirl pot.

You raise a good point -- maybe I'll put the wife's baking thermometer in the tank to check temps. The best way to avoid temp rise is to use all the fuel so no hot stuff returns to the swirl pot -- WOT all the way!

Even though pressurizing and pumping the fuel will heat it up, some cooling takes place as it passes through the fuel lines, particularly the metal ones and once the pressure is reduced when the fuel dumps back into the swirl pot/fuel tank, further cooling takes place.

As much fuel as will be flowing through this setup, I see no problem simply due to the volume saturation and what it would take to raise fuel temps to unacceptable levels.

i'll take one shipped to 98116 please!

Man, if the demand was large enough, I think it would be a good gig for somebody -- but probably not me. Like most things, it's a lot easier to make 100 of something than it is to make one. Even if I made 100 of 'em, I think it would be a little pricey -- the fuel pump is worth around $150, the material is probably another $60 (including the fittings), and there's a lot of labor involved -- in cutting, bending, and welding.

It would be a kit with the module (including the pump and wiring, but without the external fuel lines) and the weld-in steel nutring for the fuel tank. It would be the buyer's responsibility to weld the nut ring in without blowing himself up, bend the fuel sender float arm forward in tank so it doesn't interfere, make up fuel lines, and bolt the thing in.

If you're seriously interested, I'd be happy to coach you through making your own.

I have installed one of my newer Internal Surge Tanks (Internal Surge Tank (IST)), so this original In-Tank Swirl Pot is now available. It includes a fuel tank and fuel level sender in excellent condition. PM me if interested.

i am running one of elwood's "experimental" setups.....it has been flawless with not a single hint of any pressure drop at any rpm levels. I will be freshening up my motor over the winter and then tuning for higher boost using c16. i have no fear of fuel starvation with the setup...and the best part is that the car looks completely stock from the outside!! i am running the intank pump with two external bosch units. i had them wired up to individual on/off toggle switches. for day to day street driving i run pump "a", at the track i run both external pumps just to be on the safe side.....honestly at 11psi it is severe overkill, but thats just me.

and elwood is a helluva guy to deal with!

I am interested. PM sent.

Sold.