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Join Date: Dec 1969
Location: Chicago, IL, USA
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High Pressure Fuel Lines

OK. I've just seen another reference to the fact that "high pressure" rated hose should be used for the lines on a 914 engine. My question is simple.... WHY?

According to the manuals, the fuel pump on the D-Jet system has a rated operating pressure of 34 p.s.i. This isn't high pressure. The standard rated fuel hose that I have used is rated @ 50 p.s.i. That's almost 50% higher than the pressure generated by the pump.

It would seem to me that "high" pressures are only generated within the injectors themselves, and are therefore not seen by the hoses at all.

So ... either my understanding of the fuel system is faulty (which is certainly a possibility) or all the references to "high pressure" fuel hoses are unnecessary.

Either way, I would sure like to know.

Thanks,
Howard Henneman


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Old 08-22-1999, 04:43 PM
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That's because any other line is rated less than 20 psi. Have you ever seen a gas fire in engine bay in the middle of nowhere with a hot date at your side asking what's happening, honey,,,,? Ask me how I know...

The over rated line is worth the $$$....Plus it will get you to her house in one piece...ya know what I mean???

Just my $0.2...

[This message has been edited by mikez (edited 08-23-1999).]
Old 08-22-1999, 05:30 PM
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The fuel injectors do not generate high pressure. They merely open and close to allow fuel to spray at a predetermined cone shape whenever the controler tells them to.

As for the fuel pump pressure, I don't have my spec book handy, but that seems awefully low. That sounds more like the pressure that the pressure regulator keeps the system at. Fuel injection fuel pumps can usually generate 100-125 psi. If for some reason your pressure regulator stuck, you could blow a low pressure line.

I would spend the extra money on the high pressure hose, it is well worth it.

Bobbitt
Old 08-23-1999, 03:52 PM
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here is plenty of reason to run high pressure fuel line.

yeah, it's my car... the day after i put license plates on it. http://members.tripod.com/~TFI/datyona2.jpg
Old 08-23-1999, 08:56 PM
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First, I really DO appreciate the responses that have been posted. And, there is certainly something to be said for peace of mind.

In spite of these things, however, I don't see why high pressure hose is NECESARY. I would never consider installing #2 AWG wiring throughout the car just because it might be cheap insurance against electrical fires. I think that most owners would agree that the wire sizes should be appropriate for the current carried. Except for the fact that the wiring is protected by fuses, I believe that the situations are analogous.

The fuel pump IS rated for a 34 p.s.i. operating pressure. The cheezy plastic housing of the fuel filter doesn't appear to be designed to withstand high pressures. So, I'm still sceptical as to the need for high pressure hose.

I'm going to do a little research as to the specifications and test results required to label standard fuel hose with an SAE #30R7 rating. When I get that information, I will post my findings on this website.

Thank you all again for taking the time to respond with your advice and past experiences.




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Old 08-25-1999, 05:07 PM
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First off, I do know that the fuel pump can pump the pressure up to at least 100 psi...been there. If the fuel lines are clogged a little the pressure will build up. The same concept is used with the fuel pressure regulator.

Second off, are you meaning that you are putting the fuel filter after the fuel pump? If so, you definitely have it in the wrong place. it was meant to filter the fuel before it gets to the fuel pump to save the fuel pump and injectors.

As to the question on having to use high pressure lines, I would use something that is rated at like 150 psi. That is what I am using now, and so far they seem to be just great. I don't see the point of going any higher than that.

I think the "high pressure" fuel lines are something meaning fuel injection rated...because a car with carburetors could have line that is rated at 15 psi and be perfectly happy...for that matter even lower than that...

Paul
Old 08-25-1999, 06:59 PM
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