Parallel or Series Fuel Lines

[Lextreme II]

I took a trip to a local aerospace shop and they specialized in fittings. Anyway I was going to get fittings for my custom fuel rails. Garrett and I have talked about running inlet fuel into 10-AN split into two 8-AN. From the two 8-AN goes to the fuel rails. On the otherside the two fuel rails are joined with 2 8-AN and T off into a 10-AN. From the 10-AN goes to a fuel pressure regulator. From the FPR return fuel line would be 6-AN. I assume this would be like parrallel configuration.

The head tech guy was trying to convert the original design into a series configuration. He suggested that the incoming fuel lnline would go into the FPR and have lines going to the fuel rails and the end of the fuel rail would be plugged up. The question i have is which configuration would be most efficient? What do u think? The last picture is where i want my FPR to be mounted. I would like to mount squarely into the end of the fuel rail if that is possible.

 

[Red Supra]

I think you are overdoing the lines. Your proposed setup will flow to 1500 horsepower. For you i would do 2 6an feeds into each rail. Both rails should outlet into the fuel pressure regulator and will flow enough fuel for over 1000 horsepower.

 

[Lextreme II]

I think my fuel system is over killed. 6-AN sounds good. I would say 8-AN inlet and 6-AN. Here is a picture what i have in mind. I will run the inlet fuel line under the upper manifold and make it look clean.

 

[cribbj]

David, one thing you ought to consider with this fuel system is excessive circulation of fuel at idle and low load.

Some folks install twin Walbro's and run them all the time. This means at idle you've got 140 gals per hour being pumped when the engine is only needing 2-3 gph to run. All this circulation heats up the fuel, causes vaporisation, and you'll lose top end power. Ever shake a 2 gal container of gas and notice the pressure release when you crack the lid?

At Cat we used to dyno engines on a big water brake which had a fuel system that was setup for the largest engine we made. We noticed that after the engines had been on the dyno for several hours, they no longer made full power. Measuring the temperature of the fuel, we found that it had increased 20-30 degrees over ambient. Once we installed a heat exchanger in the fuel return line, all was well again.

Instead of a fuel heat exchanger, you ought to consider a method to adjust the pump output to match the engine's demand. Some people stage the pumps by running one at idle and low load, then bringing the other one on when the engine is under boost. This really isn't matching the demand, but I suppose it's better than nothing.

The OEM's use PWM circuitry to vary the voltage to the fuel pumps, which is probably the best way to vary their output.

John

 

[Lextreme II]

Which Fuel System Should I Use?

Here is a diagram below i drew up. It contained two fuel systems. Which one should i use? I will be running two 255 L/H Walbro fuel pumps and 8 1000 cc/min injectors. Most likely it will be control by an Autronic SM2.

 

[cribbj]

I think your -6AN system is enough to supply more than enough fuel for whatever you can coax out of that motor.

Besides being overkill, with the other system you may have some problems with those larger fittings in the tight spots.

Don't forget some pulsation dampners on the rails. Gasoline is a nearly non-compressible fluid, and without PD's, you're sending thousands of little hydraulic shockwaves throughout the fuel system with the injectors opening & closing.

John

 

[mycarhasposessedme]

This is my system,
-8 hose from the surge canister feeding to a Y piece with -6 outlets feeding to each rail, then -6 returns to the fpr.