Will a -6 fuel return be big enough if im using a -10 feed line? Or is -8 needed?

 

really just depends on how much power you plan to make and fuel you will be flowing.

 

weldon db2015a, 50 base, -12 to a -8 after filter, and using stock feed as return. logginf ruel pressure, no issues.

 

Return line size will depend on the fuel pump not the feed line size. Most pumps on the market are fine with a 6 return.

 

Why....

 

if the pump has a rather large output, it needs a larger return to tame it. putting a walbro on a -16 line wont make a difference if it were on a -6 line.

putting a pump that can flow over 200gph, cant get a low enough base because of the restriction in the return line.

remember that the fuel pressure regulator is a restriction in the return line. it regulates by how much fuel it lets back to the tank. if the pump is more than the -6 can handle, even with the reg all the way open, there will still be enough of a restriction to cause an increase in fuel pressure.

hope i didnt confuse you. i think i confused myself haha.

please correct me is i have given any misinformation.

 

it has dual bosch 044. the reason i ask is i have a aem fpr mounted on the rail which is -6. So i guess my question is...will this regulator work or do i need to purchase an inline bigger fpr. Im shooting for 700-800hp. Im at the end of the build and it would be nice to re use parts if possible but if i need to purchase a better regulator then so be it....

 

The AEM reg an -6 line should be fine for that.

 

6 AN hose will flow approx. 1100 lb/hr before it presents a significant restriction.

World of Outlaw 410 SBCs making 860 hp on methanol are plumbed entirely in 6 AN hose, feed & return.

As long as your bypass volume doesn't exceed ~1000 lb/hr, 6 AN hose is plenty adequate.

The other thing to think about is: how big is the return orifice in your P.R. valve? Most are between .190" and .250". The ID of -6 hose is .344".....

 

^ i like having scott posting around here, lol

 

Doesnt base pressure have an small effect on what your return size needs to be? If your running a base of 43psi on a dual 044 setup you have to return alot more fuel to the tank than if you were running 100psi base...

 

You're absolutely correct, the higher your base pressure is, the less volume your pump will flow.

In your example of twin 044's: at 50 psi combined they'd flow ~840 lb/hr and at 100 psi combined they'd flow ~700 lb/hr, so at either pressure a -6 return line is still plenty adequate.

 

What about returnless fuel setups Scott? What are the advantages of that and why would one do that vs. a return fuel setup?

 

"returnless" systems still have a return, they're just not in the typical location.

Pumps always have to flow more than the injectors are capable of, if they didn't, as soon as your injectors matched the flow of the pump, you'd have 0 fuel pressure. So since you're always pumping more volume than what's needed, there has to be a way to 'dump off' whatever volume the injectors don't need (pr valve). Fuel systems are just circulatory systems. Nothing more, nothing less.

So OEMs put the PR valve right on top of the pumps inside the tanks to eliminate the return line, but the pr valve is most definitely still returning fuel, it's just already in the tank.

The benefit of this is: the lack of running a return line (obviously) and since the fuel isn't circulating through the engine compartment, it doesn't heat up.

The drawback to plumbing it like this is: if an air bubble ever made it past the pr valve, it has to go out an injector, which will cause a lean condition of varying degree in that cylinder. In an OE application with the pump submerged in the tank, odds of sucking up a bubble are low unless you run it out of gas. Also, heat soak can form vapor bubbles in the fuel rails after you turn the car off, but OEM's still get away with this by purging those bubbles out during the initial crank (test) pulse.

In a more 'race oriented' application, where you may be using an in-line aftermarket pump, tank or cell, sump, various pick-up and return locations, higher g-forces, etc., odds of sucking up an air bubble are much greater and the impending lean condition even more critical to the engine.

We do a lot of show cars that mount the pr valve after the pump under the car to keep everything hidden, but that's the only example I can think of where we would endorse plumbing it like that.

I'd say stick to a return style system for anything performance oriented.

 

Plus the fact that in a turbo application, a 'returnless' system is usually not referenced to manifold pressure, which means your injector performance will suffer and you'll run out of fuel quickly as boost increases. I haven't seen any OEM turbocharged cars with returnless fuel systems, are there any?

 

If you're asking that, does that mean the GTR has a return style system?

What about the RDX?

 

The GTR has a regulator on the rail, like a normal car. lol Never seen the engine bay of an RDX.

 

rdx has a return line. passat 2.0t's are returnless iirc.

 

The SRT-4 has a returnless system as it comes from Dodge.

 

Oh man, this just cleared up about 3-4 questions i had burning in my brain!!

Good $hit!

 

turbo no, but the gt500 is returnless, but it uses fuel pump driver modules, where the ecm directly controls fuel pump output.

 

Now that I think about it, I sold some ID1000s to a guy with a supercharged cobalt ss and that's returnless. Interesting sidenote: he gutted the factory blower, turbo'd it, and to the best of my knowledge, runs pretty good at 20 or so psi. still returnless.

 

Leave it to the americans to put returnless systems on forced induction applications... lol

 

Interesting info. Thanks Scott.

Returnless would then have some benefits too besides not being heated via friction and pressure. I would imagine that with an advanced fuel system you could monitor fuel pressure and use a table to control pulse width to the pump for speed control. With that then you wouldn't have to worry about not being able to make up for what the regulator does. Basically controlling pressure via the pump instead of the regulator/boost pressure.

Does that make sense? lol

 

the ford system is actually pretty bad ***. 2 intank pumps, driver module for each, the stock pumps with a dual kb boost a pump (no im not getting into that) can support well over 800whp with proper injectors. we tickled 1000rwp (mustang dyno) twin 66's on a built gt500. the driver modules are directly controlled by the ecm for output, intill the boost a pump is installed. but even there i still think you can tweak them with the sct software. sad part is it is stock lined to the rail. hahaa. either 5/16th or maybe 3/8 never had a fuel filter off of one of them .

i say we, i built the damn car before i left evolution performance, im taking a little credit hahaa.