Timing questions and Max fuel PSI

[pokertramp]

When using a timing controller such as an MSD boost timing master, do I leave the distributor at TDC seeing as timing will be controlled from the BTM? It is the second thing that is bugging me. The other thing I want to be sure on is I know I need an electric fuel pump and regulator. Base PSI should be about 5psi. With a boost referenced regulator of 1:1 boost increase,correct? So I have figured I need a regulator that can handle say 25psi? And a pump that can handle about the same,,, such as Aeromotive's A 1000. Also, I think it would be better for me to run a return line, is that correct? Hopefully someone can tell me if I am on the right track. Also with the BTM I plan on running MSD 6al with the classic inline HEI,,,good setup? Thanks in advance for anyones input.

 

[addo]

A return style regulator is miles ahead of the others, and really a necessity for forced induction.

Fuel pump can be sized by looking at BSFC, or CFM under pressure, and making certain the pump can meet that demand.

For your hard lines - 3/8 is overkill, but the good thing about it is, if you accidentally crush some part of it there will likely be plenty of flow capacity left. Return line of 5/16" is nice because you can feed a wire through if it gets blocked, or you suspect it is.

I think you could run a regular DS-II curved for the off-boost revs, and save money there.

 

[Bort62]

For the fuel pump, you need to make sure that it's max output pressure is higher than your max anticipated pressure.

So, if you plan to run 5 psi base fuel pressure, and 20 PSI of boost (w/ a 1:1 reference) then you need a fuel pump that can handle at LEAST 25 psi.

A bypass style regulator will give you much more consistent fuel pressure.

 

[StrangeRanger]

Please clarify one thing: this is a blow-through setup isn't it? None of your concerns apply to draw through.

 

[kirkallen143]

AND, always have your return larger than your feed line. I run 3/8" feed with 1/2" return.

BSFC (brake specific fuel consumption) is the measure of an engine's efficiency. It is the the rate of fuel consumption divided by the rate of power production.
For a turbocharged engine, it run b/tw 0.55 - 0.6.
On a NA motor, it is around 0.45 - 0.55.
And a supercharged engine is, 0.6 - 0.65.

First need to find out how much pressure you need:

P = (base fuel pressure) + (boost pressure) + (line losses)

For my application, base is 7psi + 10psi + @5psi( can generally assume 5psi, if more bends are in the lines to the pump, then the losses will be more).

So: P = 22psi needed for my application

now how much fuel we need will be dictated by how much horsepower we plan on making. This is where BSFC somes in.

Fuel required = (target Hp) * (BSFC)

In my case I wanted 250Hp for my inline six, so:

Fuel required = 250 * 0.6
Fuel required = 150 lbs/hr
(many injection pumps measure in lbs/hr, if you want to know gal/hr simply divide by 6)

Fuel required = 150/6 = 25 gal/hr

So at this point I know for my application I need a pump that flows at least 25gal/hr @ 22psi. That's when you go to the pump charts and look at their performance curves and what they flow at specific pressures.

In this case I choose the Walbro GSL 392 inline electric: It will flow 68gal/hr @ 22psi, more than enough (and can use the same pump if I ever switched over to EFI).

And that's how I found it (well, with a little help from the guys over at turbomustangs), simple huh?

Good Luck,
Kirk

 

[XPC66]

Why the larger return than the supply?

 

[rust collector]

The way I think it is, is that the regulator should regulate, and not the return line, kinda...
I guess someone that has a better idea will come along soon...

 

[Anonymous]

I run 3/8" supply and return. The return works hardest at idle when the engine uses very little fuel.

At full boost I am returning very little, if any, fuel back to the tank!
I use about a gallon per 1/4 mile run.

 

[Bort62]

I also run 3/8" OD supply and return. -6 AN.

 

[Anonymous]

I usually run the return line the next size smaller than the feed line, same as all the Ford vehicles I can remember seeing in the yards, etc... 3/8 feed and 5/16 return or AN8 feed and AN6 return.

If 3/8" line is big enough to feed the engine, and the engine will always use some while it's on, then the volume returned to the tank will always be less.
Joe

 

[wallaka]

Well, the aftermarket pumps can push a lot more pressure and more importantly, volume, than the stock ones. The return MUST have little or no pressure on it. If it has any pressure, it will not work correctly and could be damaged. It's never a bad idea to have equal sizes on the return and feed.

 

[XPC66]

Honestly, I don't understand the thinking of equal or over sizing the return line. On a NA carby the reiturn line should have enough impedance to overcome the combined carby bowl pressure and needle impedance, otherwise it will tend to starve.

On a turbo motor application the supply line pressure requirement will rise significantly, due to the FPR squeezing flow bacjk to the tank. I doubt there would be any regulators with 3/8" orifices, let alone the pinhole in the bango fitting.

I did a quick calc based on 6 metres of 3/8" (10mm) pipe.:

Petrol viscosity 0.006 kg/m-s
Density 737 kg/m^3
500kW engine =0.064 l/s
Pump pressure = 14 psi (97 kPa)

result is ~ 0.815 m/s, 4.39 kPa pressure drop .... hardly any head at all on a pump.

Using 6mm (1/4") pipe it is still only 2.264 m/s and the drop about , 57kPa, which is still very respectable for a return line, seeing it's based on no fuel being used by the engine.