How Much Does Size Really matter?

[Ace]

...In fuel lines, that is? Reason I ask is, I'm pondering finally getting around to upgrading the stocker fuel lines. I've got good flow with the mods I've already done to the the filter and pickup, steady around 15psi, even at WOT. Just anticipating some new injectors someday. Maybe I'll need a bigger main feed line. I'll do a 3/8" line from the tank to the filter. But I was looking at the return line where it leaves the IP, and looks like a REALLy small line. Like maybe 1/4" at most. Yet occasionally I see talk about upgrading the size on that return line. What's the reasoning? Does the VE actually return more when it is fueling more? I'd a thought that was just pressure regulated somehow. Does it need more flow out the return at some point?

Any hints or tips appreciated....

[dpuckett]

If you're going to replace the line from the tank to the lift pump, go with 1/2"- less restritction, esp if you have a club or crew cab. I think BC847 did a write up about upgrading your pickup in the tank to 1/2" as well, on the DTR.

DP

[cummins king]

it depends on how far you want to go, 3/8s is more then enough on most of the truck around here, but if your going to a 14mm with all the goodys you might acualy need the fuel from 1/2 inch line

make sure when you do the up grade you double and triple check the conections so you dont have any air leak because you will have nothing but problems

the idea behind a bigger return is so you keep flowing cool fuel through the ve, its more for the 14mm head, i have stock return lines, but my return from my regulator is 1/2inch lines

and the rest of my system is also 1/2 inch

[nooblet]

Thats a very personal question you jerk.

[Ace]

I already did BC's tank pickup mod, which results in about a 3/8" or so effective bore on the pickup, depending on how much you open up the tube where the basket connects. Unless you mod the stock pickup or install a new pickup like a bulkhead fitting to draw out the bottom of the tank or something like that, bigger fuel lines will have zero affect on the max amount of fuel you can pull out of the tank at full boogie, regardless of pumps, filters or anything else.

What I want to know is how does the return work? It has to be pressure regulated somehow, to maintain case pressure in the VE. That being the case, then similarly it would make no sense to use a larger return line, because it would be flow-limited by that regulator, the same way the tank pickup is flow limited by the approx 9/32, maybe even as little as 1/4" bore in the stock pickup. Dunno didn't measure it, but it's pretty small.

Now if you could use different valves or regulators in the VE return to increase flow somehow, that would be another story.

[seeker1056]

I think the confusion here is that there are two return lines being discussed here - one for the ip and injectors aka - stock return line, and a new second return line for the bypass regulator which should be 3/8" if the feed lines are 1/2"

The line into the new lift (fuel) pump should be at least as big as the pump manufacturer calls for, and if that meanss installing a larger pickup in the tank, so be it.

To not do so leads to cavitation and pump burnout which could lead to ip burnout as well.

With increased ip inlet pressure and increased case pressure it is unlikely to be necessary to increase the size of the factory return orifice from the ip, or to increase the size of the factory ip return lines in order to increase return flow.

Pressure alone will look after that.

[Ace]

That's sorta what I was thinking. Once the fuel system reaches a state of unrestricted pressure equalization (kinda like diesel fuel nirvana ), increasing the line size does nothing. So the real question I'm trying to get at here is: Is that stock return line from the VE a restriction, under normal circumstances - a stock 12mm pump, turned up?

I avoided the bypass regulator concept, preferring rather to just remove restrictions in the system. Increasing the flow rate by simply removing the restrictions should return more benefit than trying to suck more fuel through the same sized hole, or push more fuel through the same filter with higher pressure.

It's less complicated, too.

[apwatson50]

The banjo bolt on the return from the IP has a calibrated hole in it to regulate the volume of fuel let out of the pump based on the case pressure. The hole that fuel must pass through in this bolt is very small, I haven't measured it but just guessing i'd say 1/16" diameter.

So with that being the case I don't think you would need to increase the size of the return line.

[KTA]

Stock return line is plenty.

[cummins king]

yes leave the stock return because if you open it up you will drop the case pressure and then you will lose timming

if you going piston pump you need or you should put 3/8s lines to it, and yes you should put in a new pickup

[Ace]

It's got a piston pump and actually runs really well now fuel pressure-wise on the stock 5/16" line. I have a larger filter and the BC pickup mod and it runs down the road with the piston pump at overrun on about 16psi. Drops all the way down to 15psi under load, which is I believe what the relief pressure is set to on that pump.

I don't think there's anything you could do with the return line to affect case pressure, unless it'a a restriction, which KTA says it isn't. I was just worried about what issues (if any) might be involved with that. Sounds like you could hang a garden hose off the return port and the same amount of fuel would be coming through it as before.

So I'm trying to 2nd guess the fueling stuff now, wondering what's coming into play if and when I decide to take the next step and get some bigger injectors and a new turbo(s) . There's no possible way to improve fueling with the stock injectors at this point. But maybe could use the bigger feed line with bigger injectors. I may just wait on that and put the injectors in 1st, to see what fuel delivery difference they make in terms of post-filter psi, just out of curiosity.

[MikeThomas]

Dang, only dropping to 15psi under load? Are you running the low pressure LP, or a second gen one? I only ask because I can suck mine down to 6-ish.

[Ace]

Mine was that way too, until I got rid of all the restrictions. Now the 3220 (15psi) piston pump seems to be pretty much running free. I explained the steps I took to get there in a little more detail here:

http://www.1stgen.org/viewtopic.php?t=2276&highlight=

The stock filter and pickup are major restrictions. You can run whatever pump/psi you want and it won't pull that much more fuel through those things. Eliminate the restrictions, and it'll flow plenty of fuel - even through the stock feed line.

[bgilbert]

Ace, what filter are you using, where is it mounted and how is it plumbed?

[Ace]

Bill, I honestly don't know exactly what this filter is. I found the head on eBay and then looked up the biggest sized/smallest micron filter that fit the mounting thread. I think maybe it's for some kind of IH combine, but not sure:

http://stuff.is-a-geek.net/PhotoAlbum/C ... TD_122.jpg

The plumbing looks really weird but is actually simple. Those "Y's" are just feeds for an elecrtic pump running in parallel to the piston pump, and another "Y" that goes off to the gauge, post filter.