Fuel Line and Fitting Discussion

[fabr]

Just for the fun of it. Consider the old 4500 Holley carbs and the largest needle/seat available for it. 2 of them on the old prostock drag cars would make shit loads of HP at 8000+ rpm. The largest orifice size was .150 and around 10psi would feed them ,no problem. Now for some math,each needle/seat would have an inlet area of .0176 sq.inch. 4 of them would be a total of .070 sq.inch. A 3/8 ID line with a fitting ID of 5/16 has an area of .0764-nearly equal to the combined total of the 4 needle/seats. Ignoring flow losses from excessive fittings and such ,that is just enough to do the job. A 1/2 inch line size will do the job quite well even with several fittings and their flow losses.
  My point is that ,IMO and from personal experience with 900+ HP I never,ever saw a fuel pressure loss running 1/2 inch lines with standard AN fittings and their reduced ID's. The prostock guys I used to rub elbows with didn't either even running substantially more HP than I was.
 Sooooo, running EFI with much higher fuel pressure,1/2 inch feed lines with 3/8 return is more than adequate. If a person is having fuel pressure loss at high rpm,they need to look for the flow restrictions that must be present to cause such loss. Many ,many people run way too small filters and fittings(cheapos) with undersize ID's. Add to that every time a 45 or 90 is introduced into the mix , flow loss will be had. Every fuel system needs to be thought out to minimize fittings to a bare minimum and fuel filters should be much larger than most inline that are available.   
  Bottom line is that if a person feels they need an irrigation size pump and massively large lines they are just plain wrong and are spending a LOT of extra money unnecessarily.Guaranteed the manufacturers are not going to tell anyone this since they make a LOT of money selling them.
  OK,time for the rebuttals.

[Punkur67]

The suction line on the pump line does not hurt being too big. Of course there is situations where the overkill would be ridiculous. Like running a -12 to a standard pump

[fabr]

Actually it does matter. Too large(more than one size larger) line will require more "work" to pull the fuel to the pump. That is why most pumps are in the tank today.It has nothing to do with keeping the pump cooler as many believe. It has everything to do with not making the pump work harder getting fuel to it without much ,if any, suction increase that can cause vapor lock.

[dsrace]

 well my walbro 450 pump showed.....inlet id is 3/8" however outlet od is 3/8". there site said 3/8 x 3/8" id inlet and outlet.  once i snap the screen in it then the inlet will match outlet. i def agree about fuel filters and anytime you can filter at 4 microns to 10 microns the better! now those inline aem and knock offs are ss screen and rated at 60 or 100 and not worth a crap really unless space is the deciding factor then i get it.  they don't have the flow rating the fst system has nor the filter rating.    http://www.speedwaymotors.com/FST-RF500M-Replacement-Fuel-Filter-for-Flo-Max-Systems,112433.html

i know what your saying about fuel line size and od vs id does make a diff esp when multiple connectors or connections jump up and down on id sizes creating restrictions or even length of the line and is 2' vs 22'.  psi vs flow of the pump are a huge part of supplying enough fuel as we all know and diff pumps have diff flow ratings. but all these variances are what dictate needing 1/2" or 3/8" feed line.

[fabr]

well my walbro 450 pump showed.....inlet id is 3/8" however outlet od is 3/8". there site said 3/8 x 3/8" id inlet and outlet.  once i snap the screen in it then the inlet will match outlet. i def agree about fuel filters and anytime you can filter at 4 microns to 10 microns the better! now those inline aem and knock offs are ss screen and rated at 60 or 100 and not worth a crap really unless space is the deciding factor then i get it.  they don't have the flow rating the fst system has nor the filter rating.    http://www.speedwaymotors.com/FST-RF500M-Replacement-Fuel-Filter-for-Flo-Max-Systems,112433.html

i know what your saying about fuel line size and od vs id does make a diff esp when multiple connectors or connections jump up and down on id sizes creating restrictions or even length of the line and is 2' vs 22'.  psi vs flow of the pump are a huge part of supplying enough fuel as we all know and diff pumps have diff flow ratings. but all these variances are what dictate needing 1/2" or 3/8" feed line.

Agree 100% depending on ultimate HP needs.Honestly,a well designed 3/8ID  inlet and supply to efi and regulator if after throttle body/injector rail setup will be quite adequate for 4-500 HP and 1/2 for 4-500+ HP. Just as a rough rule of thumb.

[dsrace]

yep but if in doubt go 1\2" where you can i suppose. i dont know which order bo went but i know the larger line change was before ditching the two inline filters for the fst system and i`m not saying the fst is the best. i like it cause it works well for myself and filters at the rating i pre fer plus flows more fuel than my inj`s flow so can`t go wrong for myself. the added bonus of a screw on filter like an oil filter is a very nic bonus too! now imo even though the 450 only has an 5\16" id on outlet once can still jump right out of the tank to 3\8" or 1\2" and be fine. i bought .....from gm dealer...the gm flex fuel sensor. i did this as enemy`s has proven very accurate and reliable both on manul tests and through gauage dececting content of ethy fuel. the microsquirt has a unique option of taking that info ( if you give it control of it) and adjusting timing and fuel map if a lower ethy content is registered. nice safety for saving your engine. now that line that pass`s through that sensor is also only 5\16" id. so i will try to keep that as close as possible to the pump outlet then jump in id size. it uses a quick resease fitting same as the ls 1 does and redily available at speedway. i haven`t looked yet to see if they offer one that jumps outlet size, but i will. and absolutely the reg needs to be after the fuel rail. wouldnt that be a bastard of a gremlin to find with the reg before the fuel rail lmao  but on the same note the higher hp also needs a fuel rail capable of flowing enough fuel as well. not all stock rails are large enough for that. the stock one on the t bird was too smalle guys have made them work to 400 + but for $100 i bought a larger one rated for 600 hp for future plans.

[fabr]

[BDKW1]

1/2 inch feed lines with 3/8 return is more than adequate.

You always want your return line larger than your feed line.

[fabr]

You always want your return line larger than your feed line.

Why? Especially if the feed line is oversized for the HP produced in the first place.At the most the return would be equal to feed.

[BDKW1]

At idle and low throttle situations it can mess with you pressure regulator if you have more restrictions down stream than up stream. WFO, does not matter.

[fabr]

[Outlaw]

I'm really new to all this, so forgive my confusion. I don't understand reference to "return" fuel lines. Anything I have ever worked on only has one line from the tank to the fuel pump and one line from the fuel pump to the carb.

[dsrace]

carbs don't have return lines. fuel injection (FI) do because of the higher psi and flow. for anyone that says my bike is FI and only has a feed line, you are wrong. it has "a" feed line and a return port that is built into the pump housing that you cannot see.     

now bdkw1  ........i have always ran 1 step smaller id return lines simply because the reg isn't returning the same amount of fuel the pump is delivering nor even at the same psi. what ( in your experiance) has/did/does it do to the regulator?

fabbr i have actually read those # on fuel line size on there site but saw no reference to fuel type. we all know the we need larger injectors as we consume more of the alky fuel types so it would stand to reason imo that we need a slightly larger feed line for the hp range. now that being said where you pasted up to 600 hp 3/8" is the spec from aem....where i will have to cap at 400 hp for my trans to even hope to live, even on e85 tech i should be fine at 3/8" but if poss i would feel better at 1/2". personal choice however the simplest route with the least amount of adaptors/couplers is of course how i will go.

[Outlaw]

Thanks ds, got it. Does that also apply to fuel tanks that have return lines?

[fabr]

carbs don't have return lines.My race carbs were set up with the regulator AFTER the carb inlets and use a return line.
 Just because it is a carb setup doesn't mean you can't plumb it with a return line. fuel injection (FI) do because of the higher psi and flow.It has nothing to do with injection. FI can be setup just fine as a returnless system. Any aftermarket FI can be setup both ways. It makes zero difference to the injectors. It DOES make a difference to the pump though since the continous flow through the pump keeps it cool. The FAST EFI I just installed has provision for a solid state relay that continuously cycles the pump to maintain consistent pressure without a regulator using just a pressure sensor if a person wished. I wouldn't but,it can be done that way.Much harder on the pump. for anyone that says my bike is FI and only has a feed line, you are wrong. it has "a" feed line and a return port that is built into the pump housing that you cannot see.     

now bdkw1  ........i have always ran 1 step smaller id return lines simply because the reg isn't returning the same amount of fuel the pump is delivering nor even at the same psi. what ( in your experiance) has/did/does it do to the regulator?

fabbr i have actually read those # on fuel line size on there site but saw no reference to fuel type. Those numbers were for gas. Using E85 would require a bit of adjustment as you know. Yes,I would go 1/2" feed though as it will not harm a thing.As for return,like you,I use 3/8" but Aeromotive says to stay same as feed. Makes sense as bdkw points out though even though I've never seen an issue with a next size smaller return.we all know the we need larger injectors as we consume more of the alky fuel types so it would stand to reason imo that we need a slightly larger feed line for the hp range. now that being said where you pasted up to 600 hp 3/8" is the spec from aem....where i will have to cap at 400 hp for my trans to even hope to live, even on e85 tech i should be fine at 3/8" but if poss i would feel better at 1/2". personal choice however the simplest route with the least amount of adaptors/couplers is of course how i will go.