Fuel System Setup.. Line Size Recommendations

[Gareth87]

Hi All,

Been reading up on fuel line size in the forums here and it seems that 5/16ths size line which is about 8mm ID, (ie, standard skyline size) seems to be sufficient for 500 - 550hp plus. (This will be my target)

Just want to ask if anyone sees any issues with the following..

My feed to the fuel rail from a Walbro 460lph will be 5/16ths rubber hose from the pump to the hard line under the car and rubber hose again to the rail.

Rail to reg is also 5/16th and reg back to tank is 5/16th split into 2x 1/4" hard lines. (original carby setup)

All other overflow and feed lines are also 5/16th.

Only issue that I'm concerned with is that I believe the Walbro 460s have a 3/8th outlet and I didn't want to downsize from 3/8th to 5/16th after the filter... Will this be an issue??

Thanks for the feedback in advance..

G

[scotty nm35]

The 460's outlet can squeeze into the 5/16 hose with a little persuasion. My evo runs 6mm return with the same pump, you will have no issues.

Make sure you check the fuel pressure if keeping the stock reg to make sure it doesn't skyrocket. I have only ever fitted one using the Nismo reg, and I know the stock s15 one can't flow enough.

[Gareth87]

Hey Scotty, no worries and thank you for your help throughout the recent months during my research on this. As you can understand, I don't want to get to my dyno slot and have overlooked something.

Using a sard reg so should be good.

As long as 5/16th lines can see over 500hp.. ill be happy.

[scotty nm35]

As long as 5/16th lines can see over 500hp.. ill be happy.

I have made well over 400kw on factory lines, the only issue was the fuel filter in a few cases. Changing that to a 40 micron stainless mesh filter fixed any flow issues. Worst case just bypass the stock filter on the dyno.

[Blackkers]

Hey Scotty I've been meaning to buy one of those 40 micron stainless filters that seem to be the rage these days. Whereabouts do you get them? Thanks

[scotty nm35]

I use GJ drivelines for the earls. Motorsport Connection is another a good supplier for Speedflow etc. Even Scotty's Customs usually keep one or two in stock for customers.

[Gareth87]

I've just measured the inside diameter of the hardline running along my car and it's 6mm

Of course, 5/16th fuel line has an 8mm diameter and I am setup to run 5/16th from a walbro 460. I figured the hardline would be 8mm ID as well but now I am concerned I will have a flow issue.

Scotty, you've mentioned to me that 5/16th line will be fine but are the standard hardlines on a skyline 6mm ID as well?

[scotty nm35]

No, but the return line on the Evo is 6mm.

Try it out, should do the job I guess. Otherwise run a braided feed under the car.

[MJTru]

This is interesting. Im planing on max 800hp thats to the crank. Will number 6 feed work for this goal and number 8 for the return. I have removed the hard line from my r32 gtr. Im planning on running the braided stuff.

[scotty nm35]

I would be swapping the lines around, you want the larger one on the feed usually.

Power isn't the measurement, it depends only on your pump capacity. If you had a 2000hp pump you will need larger lines and reg.

[MJTru]

Thats interesting. I always thought return line has to be bigger. Looking at the hydraulic machines at my work. All the return line are bigger. If the fpr can't return the fuel fast enough because the lines become the resistance and if that becomes the issue why have a fpr if it cant regulate the fuel pressure.

Can anyone else contest to this fact Hmmm.

[scotty nm35]

Most regs only have a 2mm hole to return fuel, how could a 6mm line be a restriction if that's the case? Yes, the return is low pressure, but it won't be that much of a restriction. As long as the return can flow more than the reg needs to bypass (while the injectors are off) you are fine. Even better with the fuelab style reg which automatically slows the pump down.

More important than the return line size is to remove (or drill out) the vac generator from the fuel tank, as most cars have a restriction in there these days.

[negativecamber]

The guys at race car engineering recommend -6 fuel line to rail, -8 return to surge and even -10 surge overflow to tank.

All in the name of reducing pressure where you don't want it. Especially when using twin pumps that can handle some big flow.

[scotty nm35]

If upgrading the lines then by all means, but sometimes you need to work with what's there from the factory.

My 6an return is fine running twin 255 Walbro's. If you can run 35psi at idle then your return is large enough, any larger is wasting cash.

Large single pumps require massive lines on the feed side though, to stop cavitation.

[negativecamber]

In my case it is a full system from the ground up using E85.

[MJTru]

Im planing using 3 044 pumps. To supply my small 800cc injectors. I want to invest in a good fuel pump set up for future use. So ill spend some time looking at line sizes and the way it should set up. One trip at a high end car show should by itself lead to seeing other drag racing setups. I do feel that I should run a line that can flow my needs and more, but for some reason in my head I still feel my return should always be bigger than my feed line. But ill contact some drag racing shops and see whats going on when it comes to fuel setup.

Buying my cell and surge tank and using all the lines and fittings ill need I can see me running into 3k plus. I need to sit down and plan this out.

Does any one have the size and thread pitch for the feed and supply. Side of a bosch 044 pump. Thanks.

[negativecamber]

Do they even make a 3 into 1 block for the 3 pumps?

[scotty nm35]

All good, but a drag setup won't suit if you plan to drive the car on the road. Those of us with fuel heating issues will warn you will require a large adjustable speed pump to keep fuel temps under control.

3 Bosch pumps will look the part, but you can max 1000's with a single Walbro on factory lines.

[MJTru]

Hmm. I would disagree to a point. I feel a wolbro pump doent have enough volume, now dont get me wrong here but why would you see all these big 044 pump setup im most peoplea trunks if it isnt needed and the hp goals are around 1000hp.

I ant think no single wolbro pump can do that. I do believe that variable pump would be better but never really have had any experience with them. And for the heat issue a cooler can easily be installed.

[sky30]

I have made well over 400kw on factory lines, the only issue was the fuel filter in a few cases. Changing that to a 40 micron stainless mesh filter fixed any flow issues. Worst case just bypass the stock filter on the dyno.

where are these filters available? Got a link or pic of one?