Fuel line routing

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    How is the fuel line routed from the tank to the fuel pump on a 1930 Mod B Club Sedan? The old line was outside the frame but it wasn’t stock I’m sure.

    If the line is outside the frame where does it cross over to the inside?

    If the line runs inside the frame I assume it goes over the right rear shock. Jim


    Hi Jim, the original routing for the fuel line was inside the frame on the right side. However, the ‘C’ or channel shape of the frame acts like a heat collector or concentrator of the heat from the exhaust system. The result is vapor lock in the fuel line.

    Many people reroute the fuel line to the outside of the frame, so that the frame is between the exhaust system and the fuel line. An even more effective routing for keeping the fuel line and fuel cooler is to route the line down the outside of the driver’s side frame rail. This keeps the fuel line from crossing over or near the exhaust at the rear. I’ve routed the fuel line back inside the frame near the left rear motor mount then across the firewall, then back down to the fuel pump. I’ve put the woven ‘loom’ over the fuel line where it is visible in the engine compartment.

    Greg Long



    I was going to use the woven loom to help insulate the line but was thinking also of putting a heat shield between the exhaust and line. Running it up the Left side sounds like a lot of extra bends but I need to look at it again, on that side tomorrow. I get kinda tunnel vision sometimes. Jim


    Hi Jim, back ‘in the day’ the fuel was poorer quality, and could use some warmth to help it vaporize. This is why our engines have a well-heated intake manifold, But too much heat can transfer to the carburetor, causing fuel to boil in the float bowl.

    And, any heating of the air makes it expand, so the density of the air the engine pulls into each cylinder on the intake stroke is less dense, and makes less power. A cooler intake makes more horsepower. Pierce recognized this in ’31, or maybe it was ’32? when the carburetor got an airfilter that had a moveable intake flap/door that could be selected to draw in air heated by the radiator and engine, or cooler outside air.

    Anyway, the MAIN PROBLEM today is out Ethanol-tainted fuel. It boils at somewhere around 150*, depends on the percentage of ethanol and air pressure, or fuel system pressure.

    With a Pierce fuel pump drawing fuel from the fuel tank, the pressure in the fuel line is less than atmospheric pressure, so with too much heat, the fuel develops large bubbles of air, and that’s vapor lock.

    So any amount of keeping the fuel cool is to our advantage. Rerouting the fuel line as far away from the exhaust and on the outside of the frame is the best that can be done.

    On the highway, the ‘channel’ between the frame rails behind the engine and transmission is the passageway that the hot air from the radiator uses to exit the underside of the car. I’ve lifted a seat cushion in a car just off the freeway, and the wood floorboards are HOT, and the tools I had stored under the seat were TOO HOT to hold onto and use. So routing the fuel line on the outside of the frame would help a lot.

    I’ve had my ’33 out on a tour, running on pure-gasoliine, no ethanol.. was getting low, added 10-15 Gallons of ethanol-tainted gasoline, and leaving the filling station, developed surging and fuel line boiling just a mile down the road.. and had to run the electric pump which is at the fuel tank to PUSH the fuel forward to the engine fuel pump.. the slightly lower pressure from the engine pump caused the ethanol-fuel to vaporize and boil in the fuel lines..

    Sorry if you already knew all the above about ethanol fuel, I added it to help explain why what was good for the Pierce cars when built is not good for them now..

    Greg Long


    To add to this discussion, I would submit that it is a good idea to block the coolant flow to the intake manifold and carburetor heat exchangers for all earlier Pierce engines. This has another advantage of removing a large chunk of cast aluminum (intake manifold) from the cooling system corrosion “battery””.

    Miles Morstatter”



    Outside the Rt. frame rail sounds like the best answer. I guess I need to hold the fender on the frame to see if there is room between the body and the part of the fender that lays over the frame. I don’t want to run the line under the frame rail to the pump, unless I drill a hole in the frame to pass the line through and I didn’t want to do that. Jim



    I am going to add my radical thoughts to this discussion: the ONLY way to completely eliminate any vapor lock problem is to add a recirculating fuel line. If you want your car judged, this solution may not be for you, since there will be an additional line from the carburetor tee back to the gas tank. However, you can add a smaller diameter line and hide it in a woven insulating tubing around the lines. My ’33 would vapor lock even with an electric pump, but when I installed a return line (with a pressure regulator at the tank return), the problem was solved forever, since cool gas was always circulating by means of the electric rotary pump.




    On the early Pierce engines, some of the carburetors had hot water passageways. Since the ’20’s, the intake manifolds are exhaust-heated. The carbs are not water heated. I’ve not seen a coolant heated intake manifold on a Pierce Arrow.

    All the Series 80/81 and ’29 and later engines used exhaust gasses to heat the intake manifold. Sometimes the exhaust heating is integral to the design of the manifolds and cannot be blocked or reduced, such as the Series 80/81, and the 1929 original intake/exhaust system. on the ’30 and later 8cylinder engines a stainless steel plate can be put between the intake and exhaust manifold to greatly reduce the amount of heat transferred to the intake.

    Jim, I did not like the close relationship of the exhaust pipe as it went up and over the rear axle and the fuel line. So I diverted the line to the other side of the car. I believe I did pass the line through a piece of rubber fuel line to cushion it, and routed it over the frame and under the body. up near the front, ahead of the battery box there was an existing hole in the frame I used to bring the line inside the engine bay.

    Bob’s method is by far the best, but coes involve more work and materials. I do like the idea of using the return line to keep the fuel circulating.

    Greg Long


    Maybe a fuel filter from a 74-75 Mopar with the restricted return fitting in the side if it would be an answer. Jim

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