Fuel swirl pots, twin 044 pumps and fuel heating

[Chris Wilson]

I have a higher than stock flow capacity, but stock style and mounted high pressure in tank fuel pump (In a Skyline R33 stock fuel tank) feeding a large swirl pot at low pressure via a filter and a short -6 line. The pot feeds twin Bosch 044 fuel pumps via -10 hoses. The pumps are T'd together via 2 filters, and feed the fuel rail through a -8 line. The return from the FPR is into the swirl pot, high up via -6. The return from the pot itself is into the main tank via -6 I have read about recirculating fuel absorbing heat from the pumps and the fuel rail / engine to the point vaporisation problems occur. I was toying with having the two 044 pumps on separate relays and just using one unless on track. Engine should make a genuine 700 BHP on decent fuel. Injectors a re Siemen 800 cc. I was considering setting base fuel pressure at 3.5 bar. None of this is running at the moment. Should I be addressing anything at this stage? The car is 90% track day car, but I may MOT it and drive it occasionally on the road to and from local circuits. ECU is M800. Is it easy to make the M800 control the second HP pump? On what criteria, RPM or MAP sensor output, or something else? Thanks.

[mhd]

I think you should have a radiator with fan to cool the fuel the 044 pump heat up the fuel a lot

[Chris Wilson]

Just to add, I see some modern engines run a fuel temp sensor in the fuel rail, what corrections is the ecu set to make based on fuel temp? How important is it in a competition engine environment where emissions are not so important? Thanks. Always something new to learn

[RossB]

If you have a spare output on your ECU you can run the second pump on a Load?RPM output so that it only comes on above a certain RPM and Load. This will reduce the amount of fuel circulation and heat. Running both pumps all the time could also cause excessive fuel pressure at idle speed if the regulator is un-able to flow sufficient fuel through the return.

[IJ.]

If you have a spare output on your ECU you can run the second pump on a Load?RPM output so that it only comes on above a certain RPM and Load. This will reduce the amount of fuel circulation and heat. Running both pumps all the time could also cause excessive fuel pressure at idle speed if the regulator is un-able to flow sufficient fuel through the return.

I PWM the pumps and have pump #2 come on boost controlled from the PDM to try and keep it from heating all 115 litres in the tank.

Running a pair of Aeromotive Tsunami's here (aka Coffee Grinders) and PWMing them makes them bearable noise wise.

Last summer I noticed it would run a little funky about 2 hours into a long drive then was doing something at the rear of the car during a stop and felt the fuel tank, since then I've added some ACL heat shielding over the rear Mufflers to isolate the tank further.

[Scott@FP]

A fuel's density changes with its temp, adding a fuel temp comp is a good idea for any vehicle that has a wide swing in fuel temps per drive cycle. For most fuels 0.75%-1.5% per 10c will be right.

This is why when you tune on a higher fuel temp, run the tank low, pull in and fuel up from an underground (cool) tank, the car runs much richer at part throttle; another variable was just introduced- fuel density changed.

[RossB]

The same thing can be seen after a re-fuelling stop during a race. The good thing is that you can use a normal Bosch temp sensor to measure your fuel temp so adding a fuel temp input is not too expensive.

[IJ.]

Where would you put the Temp Sensor Ross?

[RossB]

Where would you put the Temp Sensor Ross?

In the fuel rail.

[Alex B]

Hi Chris,

I run 2 044 pumps on my GTR33 through 2 stock (supply & return) lines feeding fuel on the sides and dumping fuel from center of the rail through regulator back to the swirl port through -8 line. I used larger return line in order to have correct pressure at idle and lower loads. On previous setup with -6 return line I was unable to have the pressure lower then 3.5 bar on vacuum. Both pumps are always on together though I am thinking of implementing individual control. Did not notice any heat related problems although the swirl does get hot after couple of hours of running. My current differential pressure is at 3 bars.

One thing to note when implementing individual pump control is to make sure the fuel will not be dumped back through the second pump when it is off. Not sure about this since did not test it myself. Perhaps somebody could comment on this more. We usually remove the valves that these pumps come installed with.

I think better way would be to use Motec DHBs to do PWM pump control like OEMs do in stock cars. That way you can reduce the pump current therefore reducing the volume, heat and noise! Looking at the DHB spec sheet it seems to be possible. Motec thech gurus please comment on this.

The control table logically will be RPM x MAP.

I think that your 800cc injectors would max out before you reach the 700bhp on pump gas. Just doing easy calculation you would need 919cc at 0.6 bsfc, 80% duty on 6 cylinders to get 700bhp. So I would go with 1000cc.
If you plan to run on high octane race fuels then 800cc would be just suffice.

700bhp GTR is a beast at the streets let alone circuits! I am not sure what skills it would take to fully utilize on the circuit I do take extreme care pedaling mine in and out of the corners cold sweating in the process!

Good luck with your project

Alex