Thoughts on Fuel Line Size

ok i have worked a few early hemi the chart showing the 392 at 720 lbs is very right. a 392 head with NOTHING in it is 45 lbs. thats all most 100 lbs in BARE heads. add a total of 70-80 lbs of valve train stantions, shafts ECT.

abodyjoe said:

i agree.... yea i know its really overkill but is it really much more going to 1/2"? you are replacing it all anyway, and this way if you ever decide to go nuts you have the fuel system to support it... gonna change the sending unit too? thats only 5/16 too.. can sump the tank too i guess.

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They sell a 1/2" stainless factory replacement dending unit for our cars. About 100$ as I rememeber when I bought one last.

You "go big or go home" guys are gonna slow the car down just with the weight of the excess fuel in the fuel supply!
LOL

For a drag car, yeah, 1/2" would be the smallest that I'd suggest. For a cruiser that big is not margin for small issues, it's excessive and it poses plumbing challenges for EFI. Sure it can be done, but does it NEED to be done? 3/8 (-6) work fine and not break the bank from fittings expense. Also, have you ever looked at the usual EFI pump? It's inlet and outlet fittings are M10. Just how big of a hole can you put thru a thread with a major diameter of .394"?

My EFI pump is 5/8" in and out. -10AN I believe is the corresponding size.

I had 1/2 on my slant six car. It needed a new tank, sender, line etc. I reduced it down to go into the factory pump.

1967 'cuda said:

I'd seen this chart before and I find it hard to believe it's accurate.

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It may not be, but, if you look at the two charts the differences in the early hemi were probably aluminum vs cast iron intakes and water pumps. Most of the other numbers are right in line.

I guess my point was if that Charger would hold a 440 it would probably hold the 392.

Hv vacuum pump to 2 gallon surge tank up front somewhere, walbro from bottom of surge to carb/efi, return to top of surge and then another return from near top of surge to tank. This minimizes high pressure line to only the surge to carb/efi. Low pressure stuff everywhere else and no fuel starvation, ever. And you can keep your 5/16 stock feed line

Bad Sport said:

It may not be, but, if you look at the two charts the differences in the early hemi were probably aluminum vs cast iron intakes and water pumps. Most of the other numbers are right in line.

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Ya, I noticed that a lot of the other numbers matched. It's hard to believe that the intake and water pump would make that much of a difference though.

Bad Sport said:

I guess my point was if that Charger would hold a 440 it would probably hold the 392.

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For that matter, the Charger could have held a 426 Hemi and look at the weight on it! I imagine it'd be tough to use any of those heavy motors in a road course car.

Here's my fuel system 1/2 @ -8 for my SB 360

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I'm becoming a firm believer in the need for the full length of the fuel line to be under pressure. Modern pump fuel is formulated for EFI and it seems to me like it boils ("Vapor locks") much more easily than the fuel of the past. Not that previous fuel was difficult to boil, just seems it's easier to do these days.

EFI supply systems hold the whole fuel supply line at injection pressure, which for most of them is 40-50 psi. That pretty much stops the boiling. It is a burden to do this. You can't use the cheap fuel hose and you need to either use fittings that don't require hose clamps ("Push-Locks" being my preference) or you need to use good hose clamps. This means using an electric fuel pump with the associated safety wiring (oil pressure kill switch usually). And it usually means that a by-passing type regulator and a return line are also needed. I used the existing 5/16" supply line for the return.

As an experiment I've been using the EFI "Barrier Hose" on Push-Lock fittings on the '65 Valiant (mostly a DD) for about a year. No issues, no concerns. The FC-332 & equivalent hose that these fittings are designed to be used with isn't significantly more expensive, it's just not as easily obtained. It is also not quite as flexible as the fuel hose.

The OP didn't ask for this, but while I'm thinking about it, I am using the GM EFI fuel filter. Might need two of them in parallel for a high demand drag car, but for anything else one should be more than enough. They're rated at 10 microns (4 to 10 times smaller than a typical carb filter) and are at least equal at the inlet and outlet to the ID of a -6 fitting. Pressure drop looks to not be a problem. They're cheap and everywhere, so replacements are easy. They're fairly large, so you aren't going to plug one up very fast. And there are -6AN adapter fittings made so you don't have to use hose clamps if you don't want to. The can is stainless, so I guess a guy could polish one so it'd be all pretty and stuff. there are some pics of all of this in the link in my sig.

Adding ethanol will decrease the boiling point of gasoline.

duster731 said:

I'd do 1/2 or -8 and be done with it

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X2. Why not go bigger? You are running all new line. You can flow less volume through it, but you can't flow more volume through a smaller line. I am planning (still) at some point to go to E85 fuel and I have to run 5/8 or -10 to the fuel pump for that.

yeah that's just crazy talk unless alcohol fuel is being considered in a cruiser. Your point is valid if talking low pressure to low pressure, but -8 is beyond excessive for the need. A 3/8 line, at low pressure, will flow more than enough fuel for some serious HP. Put a high pressure pump at the tank and now the HP that it will support get into the seriously impressive zone.

As an update to this thread, the guy I got the Charger from bought it back after having second thoughts. So the 392 never got installed and is still sitting on the engine stand waiting for a project to come along.