Ok. Ive read a ton of threads on fuel line size. And da general consensus is ⅜ is what everyone needs.... Then why is every flathead i see, in mostly stock form, have ¼ inch line to da mechanical pump inlet and from pump to carb? Why wouldnt ¼ inch line be sufficient all da way from da tank? Any insite is appreciated. Thanks
Well.....a flathead in stock form only makes about 100 ponies.... So, that doesnt take a whole lot of fuel/ minute to do. Also we need to consider that the stock single barrel carb can only atomize so much fuel/minute. If ya want to make more ponies, and still have a pump that sucks fuel from a tank, you need a bigger line so the atmospheric pressure can push that fuel to the pump. But if you have pump at the tank then you can get away with a smaller line because the pump is pushing the fuel to the carb. That is another discussion though.
Ford used the 1/4" fuel line for a long time, not sure when they finally gave in and went to 5/16", probably when the Y block came out would be my guess. My 47 Lincoln had a 1/4" line for the V12, I kept the pickup out of the tank and upped it to 5/16", through a filter and upped it again to 3/8" from there to the front of the car. I don't think there was a reason they used one size or the other, I've seen 6 cyl cars with 3/8" lines and I've seen V8 ones with 5/16".
Here's an applicable story. Back in the early '60's, I knew a guy that ran a 270 HP dual-quad '57 Chevrolet Bel Aire 2 door hardtop in SS/C (I think that was the class). He was very successful, winning his class at the NHRA Nationals in 1961. The next year, he decided to keep ahead of the competition and installed the power train from the Bel Aire into a 150 two door sedan that was originally a 6 cylinder car. The car ran strong, but for some reason, was never quite up to the performance standards he had seen in the Bel Aire. To make a long story short, the 6 cylinder Chevrolets of that era had a 5/16" fuel line, while the eights had a 3/8" line. Replacing the line from the tank forward with the proper 3/8" line improved the performance on the sedan to a bit better than the hardtop. So your answer is, yes, there is a difference, but you'll never notice it until you get down to chasing the final 1/100's of a second in the quarter. The main thing here, though, is that it will not make one bit of difference if you are running a flathead.
I ran three Rochester Model H carburetors ( Corvair Carburetors ) on my 250 inline six with 5/16" line from pump to each carb. It ran Ok but never felt quite right. I rerouted the fuel line and used 1/4" line from pump up to each carb. I notice right away the engine felt better all through the little power range it had. Not sure if the smaller line raised the pressure or the volume to each carb, but it made a difference. The engine only makes about 140 hp on a good day.
Factory dual quad and FI engines had 3/8” fuel lines. 6 and std V8’s had 5/16”. I use a Chevrolet flex line from the frame to my Y-Block 56 Ford which has a 5/16” line. Ethanol friendly from Danchuk down the street.
Smaller lines do not raise pressure. Smaller lines restrict flow. Requiring a higher pressure at the pump to get the same flow a larger line would have supplied at a lower pressure.
So the problem may have had to do with over-fuelling, especially considering only 140 HP. I bet it came into it's own when up around redline rpm..............
It's not the number of cylinders which determines the amount of fuel....its the horsepower that does. Many OT cars I've owned had half the cylinders (and 1/4 the displacement) my '59 has and made more horsepower....therefore requiring more fuel. But that fuel was delivered at 100psi through the same same size 5/16 line.
Pushing gasoline is different then pulling it.. I would think overall you would flow more fuel by pushing it then pulling it.. This guy I know who builds all kinds of induction systems told me its better to use two 3/8" steel tubing lines coming from a sump in the tank going to a 3/8" x 3/8" x 3/8" tee in the mechanical fuel pump. Then running one or two 1/2" hoses.. It has something to do with velocity and the fuels ability to pull itself through the tubing..
that's a pretty good quote, there.... Pressure difference is what makes fuel move through fuel lines. A pump can create a vacuum on it's inlet, so atmospheric pressure can push the fuel from the tank, to the pump. Then the pump creates pressure on the outlet side, which pushed the fuel to the carb. The rate that fuel needs to flow, depends on the rate that it's used by the engine. So, a low power engine can get by with a small fuel line. A high power engine needs fuel at a higher rate, so it needs a larger line (all else being equal). There were a few vehicles made with 1/2" fuel line from tank to pump.
In most cases I have seen from factory 5/16 used for 1&2 barrel 3/8-4barrel. Engine size or amount of cylinders did not matter.
I had the 1/2" line from the Tank to the Carb. on my Race car But I also had 2 Carter Electric Fuel Pumps mounted in the Gas Tank. 64 Chevelle SS L88/800 hp I will never forget running the Car for the First Time and getting Beat by the Record holder by 1/100 of a Second and He changed his Class , he said when I got the Bugs out of the Car I would Beat him. ( may he Rest in Peace Dick Moroso ) Just my 3.5 cents Live Learn & Die a Fool
an old article in Hot rod stated Ford gained 5 or 6 HP on the 427 engine by changing the fuel line from the pump to the carb from 5/16 to 3/8. Go figure.
Often the size of the fittings dictate the size of the line you have to use. You have to have the correct size exiting the fuel tank in order to change to a larger fuel line. It doesn't help much to use an adapter to increase size if the original fitting is still smaller. Then at the other end of the line, you may need a certain size to fit the pump you have or the pressure regulator. Its always better to have a larger size than you need than to be slightly too small. When planning a new system install, its probably best to use 3/8 and go even larger if you have a max-motor.
3/8ths won't do you wrong for most cruisers. Of course super hi perf stuff can use bigger. Early Fords used smaller so it is the trad way to do it. Why the confusion?
Maybe if its pretty much stock, but then Hot Rodders never being satified with the status quo are apt to want to upgrade as time goes by. I figure its better to use a common 3/8 and not have to re-do it later on.
I can buy all kinds of different size lines for da price of that book. At least on fleabay. Wow. But thanks for da response
I was thinking da same thing, hence this thread. Max motor not happening. Im kinda into good running vintage with minor tweaks. I cant understand da inlet or outlet size being what it is, then using a bigger line in between. Like you said, restriction. Thanks for your input also.
So. Would it be necessary or recommended to use a 5/16 line in place of THE 1/4 inch line from the tank to the mechanical pump at that point where it would down sized to a 1/4 inlet on the pump anyhow. And i already have 1/4 plumbed fron the pump to carb with the correct Ford fitting. Trying to make sense of this.?
How much power is the engine making? If it's not a lot more than stock, then 1/4 should be fine. If it's well over 100 hp, then 5/16 would be a good idea.
The Jalopy Journal
