Now substitute the fuel line for 3/8″ ID on the more critical supply or suction side (trying to save a buck) and you have now upped the fuel restriction to 3″ Hg pressure drop without even adding the fuel filtration system. Just wondering and the boat I bought just has the vehicle fuel line in it. Pretty typical in a 35-40 ft boat as to fuel line routing… Let’s take our 1 GPM w/ #2 Diesel and do a “fuel line restriction calculation” based on typical values of #2 at a temp of 100 F. I’ll use a specific gravity of .85 and a viscosity of 3.0 centipoises (these would be reasonable numbers). One, the maximum allowed value for the pressure drop is usually 2-4 times more and the return flow is always less (at least to some extent) than the total fuel flow. Summer is comming here, so I will be getting the boat out soon to start working on it. If I remember correctly back in the days when I worked at the Phoenix Sea Ray plant then the red stripe is the marine stuff. 3/8's, 5/8's? Yes, the 2 mic will load quicker (get dirty) and the restriction would rise faster, but isn’t that what it should do? Just about everybody seems to equate fuel restriction with the fuel filtration system and it’s design, and never thinks about the fuel line as being a major factor in this equation, even when all is new and clean. Boat is a high compression 454, with a 750 holley. Units of measurement can vary, but inches of Mercury (Hg) seems to be most accepted. Brand New. Has newer Mallory Unilite distributer, and Taylor 8mm wires. Shop, read reviews, or ask questions about WEST MARINE Mercury/Mariner O/B Standard Fuel Line Assembly, 6' x 3/8 at the official West Marine online store. We’ll get to that later as that is a slightly different subject. This is an EPA – CARB Compliant FUEL LINE ASSEMBLY & Made in the USA! He asked if I was doing it as a rev limiter. Just about everybody seems to equate fuel restriction with the fuel filtration system and it’s design, and never thinks about the fuel line as being a major factor in this equation, even when all is new and clean. The U.S. Coast Guard addresses fuel line requirements in the code of federal regulations (CFR) that applies to recreational boats: CFR Title 33. Marine hose must have the SAE J1527 Style R1 rating emblazoned on the hose to pass as seaworthy. Inside the ½” fuel line the fuel would be traveling at 2 ft/second and inside the 3/8″ fuel line just over 3 ft per second. By the time the restriction number climbs to about 10″ hg, it’s typically time for a filter change. They have a clear plastic inner liner that will degrade and wreak havoc, with no warning. Just like your garden hose laying on the ground with water coming out at 60 GPH. A couple of hours tuning could really help you. Joined Jul 27, 2006 Messages 2,634. (External pumps push fuel. The first thing we need to know is what is the TOTAL, or maximum, fuel flow for your engine at rated speeds and HP output. Although kind ugly and a touch complex, it was low on restriction because of ample sizing (mostly 3/4″ pipe size) of all the fittings & hose sizes Car engines have smaller valves, less compression, and even the most popular "RV" cam used by the car guys is much smaller than the stock jet boat grind. Jul 11, 2013 #3 Re: fuel line size. I now run -12 lines out of the tanks including 3/4" ID custom made pickup tubes then from the pump to the fuel rails -10. So a -10 would be 10 mm, -20 twenty mm, and so on? Yes, you can equate the two but not as most think. 429531 $39.87. The We just ended up w/ a .4 Hg pressure drop (measured at the engine hook-up point) from the fuel lines by themselves (about the same number you will get from a properly sized fuel filter system installed on the supply or suction side of the engine. 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