Stressing fuel line size

[Pop N Wood]

I am about to plumb my fuel lines and paranoia is starting to take over. I need help deciding what size line to use, cause the time is now to make a decision.

 

What I have is a carb'd LS2 crate rated at 446 HP, but should easly get over 500 HP once I cam it. I have a Mallory Comp 140 fuel pump and return style regulator. I also have everything I need to plumb 3/8 inch fuel line.

 

But I keep reading things that says the 3/8 line is good for either 375 HP to 500 HP. also read post of people who claim to get some ungodly HP out of smaller line.

 

What do you guys think. Does the very real possiblity of 500+ HP warrant selling all the 3/8 line and AN6 fittings for 1/2 - AN8 stuff?

[grumpyvette]

the 1/2" INSIDE DIA. gives you some extra flow capacity but its surely not mandatory at the 500 hp level, have a decent return style 3/8" INSIDE DIA.system and youll be fine at that level, yes IM only too aware every chart shows 375 hp as max for a 3/8" and 1/2" for 500 hp, and yes youll be better off doing it correctly with 1/2 INSIDE DIA. lines

but Ive run several race cars at 500 hp levels running in the 10 second range with 3/8" INSIDE DIA.fuel lines

 

http://www.centuryperformance.com/fuel.asp

 

the confusion here may be that many guys look at the OUTSIDE DIA. and a 3/8"OUTSIDE DIA. has closer to a 5/16" INSIDE DIA and thats certainly not going to supply 500 hp

[Pop N Wood]

Well that is all the answer I need.

 

For what it is worth, the numbers in that century performance article are the exact same values Mallory and MrGasket list in a tech article on there site

 

http://go.mrgasket.com/pdf/TS_FuelSys.pdf

 

One thing else I have also noticed. The Russell AN6 braided hose has a significantly smaller inside diameter then the el cheapo rubber fuel line.

[cygnusx1]

Don't forget about the other variable in flow calcuation; Pressure. Even a small line can feed alot of fuel if a high pressure pump is used to produce a high flow velocity. Pressure losses will be high but it will feed the fuel.

[briann510]

For whats its worth I run 3/8 hard line into 3/8 braided in engine compartment that feeds a 525 rwhp carbed Pontiac. Have had no issues for 25 years with that line and using a 14 psi Holley pump deadheaded with no return line (just never got around to putting one on). I know other guys who's engines with similiar or less hp needed a 1/2 line.

[grumpyvette]

cygnusx1

brings up a good point I should go into, in more detail. carbs generally don,t work well unless the fuel pressure entering the carb falls roughtly in the 4psi-6psi range so you can,t stick a 14 psi pump on the fuel line WITHOUT a pressure regulator,(as close to the carb as is practical)

return style regulators tend to both work more precisely, plus in most cases they can flow more volume due to the basic design and allow the pump to run cooler than dead/head style regulators.

pumping the fuel from the tank to the regulator at higher pressures has advantages

[Pop N Wood]

the confusion here may be that many guys look at the OUTSIDE DIA. and a 3/8"OUTSIDE DIA. has closer to a 5/16" INSIDE DIA and thats certainly not going to supply 500 hp

 

Upon further review, I have 3/8 OD tubing with a 5/16 ID.

 

The Mallory pump also has a 14 PSI dead head pressure. I ended up getting the larger capacity 140 GPH pump since it had a better package price with the return style regulator.

 

So when brian510 says 3/8 hard line, that is almost certainly OD. 525 RWHP sure beats 500 crank HP. Plus the Z car should have a shorter run of fuel line than most cars.

 

Ehhh.

 

By the way, isn't all tubing specified as OD?

[DemonZ]

I do believe tubing is OD.

 

 

This is somewhat related. I have some concerns about safety in the event of a crash. SS lines are supposed to be a pain to work with, and I'd like to do this only once (yeah right). Would SS hardline be the toughest most practical tubing (would it tear and leak vs. a fexible SS braided would give)? And what kind of joints to use?

 

 

I have an inertia switch that will cut power to the fuel pump, and an FIA approved Fuel Safe cell.

 

 

Reason I would like to design some good safety into the fuel system is, I recall a vid of a fatal accident involving a Porsche that got t-boned on a track and burst into flames, and also Don Schroeder (of Car and Driver mag.) was burned to death when his test car crashed and flipped.

 

 

Normally I would like to design a little "head room" into everything, but realized that would just be more fuel to get spilt in the event of an accident. So don't want to go too big.