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Fuel line sizing question
It's time to run the fuel line in my FE equipped older Contemporary that I'm restoring from the frame rails up, and I'm not sure what size fuel line to run. I have the sending unit / pickup out of the tank and I'll have the pickup line changed out to match the size fuel line that I end up running. The engine is a 600+ HP 482" sideoiler, with a single 900 CFM Quickfuel carb. I'm running two Facet blue dot electric pumps, each has 3/8" fittings. It's easy to just go with 1/2" line and play it safe, but it's bulky and more difficult to work with, and in such a small car it gets tight in some places. Do I need the 1/2" line? Does it even make sense to deal with the 1/2" line with the pumps only having 3/8" in and out fittings? Also, is there any reason to run a mechanical pump as well? If so does anyone have a recommendation on a mechanical pump that will have the correct size fittings? Thanks.
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I had ERA run 1/2" line for me and it wasn't too bad. The flow through a 1/2" line is significantly more than is possible with 3/8". I figured I only want to do this once, so I went with 1/2". My line is aluminum, and I am putting some protective covering in any area subject to road debris.
I used the following mechanical pump on my 482- http://www.robbmcperformance.com/pro...ordfe1100.html |
Hey,
I am sure others will have more info for you but as a reference point I am running a steel 5/16" without issue. The fuel lines are #6 AN to and from the main steel line run along the frame rail. This is feeding a 540 inch Chebbie engine and not a Contemporary but 5/16 is at least enough for your 482 " engine and I think 1/4 would be fine. I prefer the advantages of an electric pump but admit a quality mechanical pump is pretty reliable. Have fun,enjoy your Toy. |
The biggest clue for me to use a larger fuel line was the mechanical fuel pump that came on the engine from Roush was 8AN. I'm not an expert on the topic, but I did switch my Superformance 3/8 inch line and Superformance supplied fuel filter(same as one from Auto Zone for a few bucks) to 1/2 inch or 8AN line from tank pick up to carb along with an Aeromotive 100 micron filter. I also went with a higher cfm carburetor from Pro-Systems, different air filter, headers and side pipes. It was about a 75 wheel HP change all together, so about 475 at the wheels. Without the changes the 3/8 seemed ok, but after I started increasing flow and adding power the top of 3rd and 4th gear would drop off at times even though air fuel ratio was good.
An electric fuel pump might push better through a smaller line, but not sure. |
I used stainless tubing in lieu of a flexible hose, it will bend a tighter radius and takes up a little less room. This is 3/8" secured with cushion clamps. I think 1/2" would even be overkill for your engine.
http://www.clubcobra.com/photopost/d...icture_344.jpg[/IMG] |
Here's a link to a article Holley has on fuel line sizes..
http://www.holley.com/data/Products/...ech%20Info.pdf Thanks, Jim |
3/8" (-6) will fed up to about 500'ish hp with a pusher electric pump. A puller mechanical pump will have some trouble feeding more than 500hp with those lines.
With 600+hp, I would definatly move up to 1/2" (-8). 3/8" fittings on the fuel pump will cause some restrictions. I would be concerned about that. You're running two pumps - does that mean you have two pick ups? If so, run -6 from each pick up to the pump. Then -6 out of the pump to a manifold that's -6x2 in, and -8 x 1 out. That should maintain full flow. If there's only one pick up, I can't see a reason to run two pumps in series. Replace those two with a single high flow pump with -10 fittings. Like Aeromotive A1000 with the proper pressure regulater. To make life easy, use braided hose from stem to stern. A little more expensive, but it sure is easy to run. You can have the whole thing done in a day. |
I'm running the same pair of pumps that Shelby supplies in the 4000 series cars. They have 3/8" input and output fittings. Honestly I'm not even far enough along in the assembly to check if they are plumbed and run in series or parallel. Does anyone know? I have only one fuel tank pickup, it'll be either 1/2" or 3/8" depending on the fuel line size I end up running. I've seen some pretty strong engines in these 4000 series cars, many exceeding my 600+ HP FE. Does anyone know what size fuel line Shelby puts into these cars? I guess the basic question becomes does it pay to put 1/2" line in the car when the inlet and outlets of the pumps are 3/8"?
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Doug
You should ask your engine builder. You can email Keith C or even Barry R. I would say 1/2" as stated in the previous post you only want to do this once. While your at it run a return line just in case you want to go EFI in the future. |
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I'm still stuck on the idea that with 3/8" fittings it's useless to go to half inch line as only enough fuel to pass through the restrictive fitting size will flow. Is this a correct assumption? I would just run 1/2" since it's no big deal, but that greatly restricts the choices on mechanical pumps used at the front end of this setup. The only one I know of with 1/2" fittings on it is the RobbMc unit, and it's a $300 piece, sort of steep. Long story why I want a mechanical unit as well, but I do want one in there. |
If a fitting is 3/8", a 1/2" line between them is useless, as no more fuel than what will flow through the 3/8" fitting will flow through the 1/2" line. Just look at the Nascar restrictor plate.
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True dat - the only gain you would get with 1/2" vs 3/8" after the
restriction is less friction loss in the line which is too short of a run to be significant. |
Your dealing with a pressure drop analysis of your fuel system. The total pressure drop with 3/8" will be higher than 1/2", but not much. I don't think you will notice any difference. If you are getting at least 7 psig fuel pressure to your carb at full throttle, your Gold! If anyone can calculate the max fuel flow required for 500 HP and 600 HP engines, I will do the tradestudy to see what the pressure drop difference is for each size line.
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Still great when your wife buys you a nice timing light! Love that woman! Just tell her it works great!
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Doug
The return line doesn't have to be as big as the feed line. If you are using 3/8" feed you would use a 5/16" return line. |
The fitting hole on the fuel pump is 3/8" NPT. (at least mine is) You can get a fitting that's 3/8"NPT to fit in the pump and the other end is -8AN. They are very close on inside diameter and both are bigger than 3/8" hose or tube on the inside. Buy a couple fitting and look.
Go 1/2" or -8AN all the way. Why take a chance? (Use aluminum tube for as much as you can as it is less restrictive) |
600 hp = 1/2"
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Although most people don't do it I'd run an equal size return line as it's the opposite condition of the feed, at idle almost all the fuel the pump is delivering is being sent back to the tank by the regulator. If the return is too restrictive your idle pressure can climb above the set point of the regulator.
As most others have stated -8 (1/2), no point making the pump fight the line restriction. Not to mention over time the pump's output will degrade from wear. |
A 3/8 pipe fitting with a -8 an line works fine--the 3/8 fitting can be drilled out ti the id of 1/2 line which I use Stainless hardline with .035 wall making the fitting id only .430 so the 7/16 (.443) fine. You will have more restrictions with turns than from line size.
There are high performance mech pumps by several companies with the 3/8 npt threads and they flow enough fuel. use the mechanical pump and forget the electric ones |
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