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---- Dave <david.staten@gmail.com> wrote: HOWEVER..... if there is not a method to bleed down the rail the risk of vapor lock exists, as the rail heats, the fuel boils, and the vapor gets trapped in the line.
<rant mode on>
Vapor lock. Vapor lock. Vapor lock!
If you don't eat your peas the vapor lock boogey-man will eat your feet!
</rant mode off>
Could we please put this vapor lock boogey-man myth to rest. Vapor lock is NOT "some vapor in the line". Vapor lock, as Al says, is vapor at the pump inlet which destroys the pumps ability to pump. Vapor lock is dangerous, because the only way to recover from the vapor is to add pressure, and the only thing that is able to add pressure is blocked from doing so by the vapor. If there is some vapor AFTER the pump, it will quickly disappear once 35 to 50 psi bears down on it and it gets pushed through the injectors. In the worst case, there would be an imperceptible hick-up as a lower density volume of fuel is spit out of the injector at some point. You are MUCH more likely to suffer from vapor lock due to bringing that hot fuel back to the vicinity of the pump, than from just leaving it forward of the firewall.
The amount of angst from inconsequential matters in this thread is starting to get comical. First, there is hand-wringing about restricting the fuel flow. Really? Through a -6 line? Is there anyone on this list that is able to flow more than 20gph for any length of time without melting their engine? Try this experiment. Put a -6 line as an exit out of a gallon jug. Fill it with water and time how long it takes to empty. Anything less than 3 minutes indicates that a -6 line would suffice for the maximum sustained flow that will be needed in real life with nothing more than gravity feed. Add as many angles and banjos if you think that'll make a difference. Now, seal the container and pressurize it to 35psi. Try not to hurt the neighbor's kids with your new SuperSoaker. You'll want to trade down to a smaller size exit line so that you can actually get in a little play time before the tank runs dry. Seriously, with a -6 line you can add every kind of twist and turn you could imagine and still have multiple overkill amounts of flow. If that doesn't convince you, measure the size of the injector's blow hole. Multiply that area by the number of injectors you're using. Calculate the total exit area, then calculate how many multiples of that go into the area of a -6 line. Now consider that the injector's blow hole has a pintle as an additional restriction. My six cylinder Dakota, rated for 210Hp, has a fuel rail that looks to be about 1/4". Would Dodge be dumb enough to kill the performance of the engine by cheaping out on sizing the fuel line properly? (Don't answer that. I'm afraid of the answer.)
At the same time, you're worried about the fuel getting hot. With that much fuel flowing, if heat is being transferred to it that quickly, you either have the lines routed through your exhaust stack ... or ... hell, exactly how WOULD you get the fuel to heat that quickly? And you would you heat it that quickly without melting the hose? BTW, raising the temp of the fuel is useful. Makes it vaporize better. Even with the extremely low flow rate I had, I still got condensation on the intake manifold when it was nearly 100* outside, and I know that the fuel was at least 85*.
As for pressurized lines. 50psi is not "high pressure" for an aluminum or quality hose fuel line. You carry that much pressure in your tires, and look at how everyone treats them. It's not until you get to some significant fraction of thousands of PSI that you start to need connections more exotic than hose clamps. Fuel systems in thousands of the cheapest cars rolling down the highway prove it every day. Of all the leaks I had in my fuel system, NONE of them were in the high pressure section.
My fuel comes out of the tank, through a large filter to the pumps. The regulator comes next, with an upset in the seal to allow pressure to bleed off after shutdown. The pressure wasn't a problem. Some mysterious vapor lock demon wasn't a problem. Having pressure hanging on for days, slowly pushing fuel past the injectors to pool in the closed intake manifold, was a serious safety concern. A single line from the regulator carries fuel through a small filter (in case a pump sheds parts) up to the firewall. A vertical section insures that any fuel that is boiled from engine heat after shutdown stays forward of the firewall. FWF, a hose carries the fuel to the primary injectors that are located in the stock location using the stock rail, where it passes through a banjo joint. Another stock banjo joint carries fuel to the secondaries using the stock rail and another banjo joint. I just 50psi, silicone fuel hose and hose clamps. With 460cc injectors, I got enough fuel through to repeatedly flood the engine.
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