Just wondering about fuel line size for my RPU Tim McMaster built 309 warmed up Y block with 3 new Stromberg 97s. The Stromberg’s take 1/4” fuel line and I’m going to run a mechanical fuel pump with a fuel pressure regulator. My concern is the size of the fuel line I’ll run from the tank to the fuel pump. If the line from the fuel pump to the fuel block and then to the carbs is 1/4”, is there any advantage to running 5/16” fuel line from the tank to the fuel pump? Or, would the entire system run in 1/4” make more sense and supply enough fuel? We’re not talking high pressure or flow etc.
I always run a size larger before the pump, always done it that way. My current car is getting 3/8" from tank to pump (my pump has 3/8" NPT fittings) and 5/16 from pump to carb (my carb has 5/16" inlet). 1/4" should work OK for a small displacement engine, that's what most had from the factory. I'm just more comfortable with the next bigger line in front of the pump. SPark
Bigger is better also for keeping the larger volume of gas cooler.........................................
i have always wondered about that. if the line is big it would move through the line slower, sitting in one place longer. smaller it would move quicker and be replenished with cooler fuel from the tank. not arguing, i just always had that thought in the back of my mind. of course, a return line makes that mute.
Let's do this in an "if then" style question and answer If 1 carb requires 1/4 fuel line ,,, Then how big of a fuel line does 3 carbs require? If the Area of .25 line is .049 Then .049 x3 = the requirements of the main line feeding 3 branches. .049x3 = .147 3/8 line area is .111 1/2" line area is .196 You can look up some fluid flow charts too. 3/8 would "probably" be enough 1/2" if you plan on max effort WOT driving
I think you might want to consider that the ID of 1/4" fuel line is pretty small. I'd run 5/16" in this application. If it were a bigger engine with a decent size carb on it, then 3/8" might be called for, but most car makers got away with using 5/16" line on almost all small block engines for years.
I'd suggest 5/16 from tank to pump, and 5/16 again from the pump to the fuel distribution block. Then 1/4 to each carb. If you think you (or the next guy) might want 400ish hp, now would be a good chance to run 3/8 from the tank.
Regardless of the number of carburetors, the engine is going to use a certain amount of fuel. Pontiac found 3/8 inch line was sufficient to fuel a 455 H.O. for all street use. And as posted by others, many small blocks came with 5/16 inch. If you use 3/8 inch, would highly suggest the use of the return line, as the larger line will cause the fuel to run slower and absorb more engine heat. The return line will help cool the fuel. Jon.
3/8 line is what you want for a streeter. Your pump doesn't have to work as hard and the bigger line acts like a reservoir. You will always have fuel on tap. Here's is a little story. My old racin buddy started out with a big block dart that he street raced and sometimes grudge night at the local track. He was starving on the big end and what we did was up size the fuel line to 1/2 from 5/16 from the tank. No special pump, not trick anything just a bigger line and it solved his problem.
3/8th to and from the regulator, 3/8's to the filter, 3/8ths to the carb distribution block. Then I knock it down to the individual carbs. Everything SS other than the final Russell braided nylon line from firewall to fuel block on blower. Probably overkill but that never stopped me.
Stick with the bigger line,I assume you will be running a fuel pressure regulator and that will control the amount of gas getting to the carburetors. HRP
Larger size on the supply side to the pump is standard practice for pumps of all types. I'd go with 3/8" from tank to pump, 5/16" from pump to regulator/filter/fuel log, from there you could leave it at 5/16", or step it down to 1/4". Smaller diameter line is easier to bend if you're going to get fancy with it.
Sure A 5/16 line will feed a fuel block with 3 outlets at 1/4" sure it will, but not well. Look at the ID of the fittings being used because you'll get no more fuel that can pass thru that fitting- that will be the flow limiting orifice in the line. Don't matter if you have 4" line feeding that fittings ID
Only as good as your smallest fitting before the pump.......ah someone beat met to it. I would run 5/16" IF your smallest fitting ID is the same.
Speaking of fittings, it's worth comparing different ones from your big ol' box of fittings because some will have larger drilled holes than others, even if they are nominally the same fitting. You can drill the holes larger in some cases, but you have to use judgment in how far to go without getting the walls too thin.
All good info guys keep it going. After consultation with a rodding buddy today I’m leaning towards 3/8 from the tank to the pump and then 5/16 to the regulator and the log, then from the log it will be 1/4 to each carb. All ni cop lines.
This was a very useful thread for me - I'm busy with an almost identical 3x2 Y-Block set up. Did you eventually figure out the fuel line sizes and how did it turn out?
Yes, I did, I ended up ordering the necessary fittings and went with 3/8" from the fuel tank and then 5/16" for everything else. Plenty of pictures on my build thread. https://www.jalopyjournal.com/forum/threads/26-t-roadster-pick-up-build-thread.460009/page-59
3/8" supply, 1/4" return.. With todays moisture sucking gas, a return is almost mandatory.. Just tee off the port feeding the carburetor and run back to the tank in 1/4"..
It isn't the amount of carburetors, it is the HP of the engine. You could have a 300HP with a single 2 barrel or 6 - 2bbls and the fuel requirement will be the same. An important consideration is what fittings do you want to use? If you are going brass/steel and 'inverted flare' then I'd run 5/16ths. If you wanted make it easier I'd go with 3/8ths to use -AN fittings, you can transition from 3/8ths to 5/16ths and transition from Inverted Flare to -AN but those fittings are hard to come by and it'd take 2 or 3 different mfgrs inventories (ie, Aeroquip, Fragola & Red Horse) to complete the system. I am trying to get the stuff to make the 1/4 & 5/16ths woven hoses with crimped fittings like from the '50s but I'm not there yet.
Check out my build thread, I used all inverted flare and some 5/16 " compression fittings I ordered from Stromberg. I used the proper fittings and the 2 short pieces of rubber hose I used special fuel injection hose ( for ethanol ) and crimped sleeves so no hose clamps. Nice and clean and neat.
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