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Old 08-22-2010, 12:11 PM   #1
Tugmaster
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Default Fuel filter: Before or after the fuel pump??

I ordered my new carbs from Tom Langdon for my 250 straight six last week. While I was talking to Tom on the phone the topic of fuel filters came up. I mention that I had mine mounted on the frame rail just before the fuel pump. He said having a filter mounted before the fuel pump was a very bad idea and that I was asking for trouble. He explained that the way a fuel pump works that it will cause vapor lock.
I've ran my car in some very hot weather and have not had any problems. If it aint broke it doesn't need fixin. But.... Could I at some point have problems.
Where are you guys running your filters? Before or after the fuel pump? Thanks, Todd
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Old 08-22-2010, 12:14 PM   #2
pitman
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Default Re: Fuel filter: Before or after the fuel pump??

Maybe run a screen before, and a filter after the pump?
Keep them cowl-tank born rust flakes at bay?
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Old 08-22-2010, 12:16 PM   #3
Gotgas
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Default Re: Fuel filter: Before or after the fuel pump??

I prefer to have at least a screen to keep large debris like tank rust out of the fuel pump. If you have a clogged filter before your pump, I suppose you could have issues with vapor lock or fuel starvation, but at least you didn't run a bunch of trash through your pump.
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Old 08-22-2010, 12:17 PM   #4
J.Fishbeck
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Default Re: Fuel filter: Before or after the fuel pump??

I have always used Fram G3 filters, before my pumps. I haven't ever had any problems with vapor lock. Kept away from any heat, I don't see how that could cause any problems.
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Old 08-22-2010, 12:22 PM   #5
sixinarowjoe
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Default Re: Fuel filter: Before or after the fuel pump??

no probs here -i run them before and after the fuel pump -keeps my holley webers nice and clean
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Old 08-22-2010, 12:23 PM   #6
1941ihkb5
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Default Re: Fuel filter: Before or after the fuel pump??

Most of mine have filters before the pump. No problems so far...
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Old 08-22-2010, 12:29 PM   #7
sixinarowjoe
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Default Re: Fuel filter: Before or after the fuel pump??

dont think your gonna have a prob with your 6 seeing as the fuel line is on the opposite side of the exhaust manifold
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Old 08-22-2010, 12:42 PM   #8
tommy
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Default Re: Fuel filter: Before or after the fuel pump??

Mechanical pump on the engine...no pre-filter.
Electric fuel pusher pump at the rear...a filter to protect the pump.
It's worked for me for all these years. That's the way the factories did it.
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Old 08-22-2010, 02:14 PM   #9
TexasHardcore
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Default Re: Fuel filter: Before or after the fuel pump??

I always use two filters, one before the pump, one after. I change them everytime I do an oil change. Cheap insurance I guess. Never had a problem mechanical or electrical. I always use the clear plastic Fram fuel filters.
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Old 08-22-2010, 02:50 PM   #10
shortbed65
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Default Re: Fuel filter: Before or after the fuel pump??

I've read more than once - suck with a screen - push with paper
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Old 08-22-2010, 02:58 PM   #11
fleetside66
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Default Re: Fuel filter: Before or after the fuel pump??

I have one before & one after...no problems (sbc with a standard mechanical fuel pump).
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Old 08-22-2010, 04:03 PM   #12
canman
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Default Re: Fuel filter: Before or after the fuel pump??

Pressure differential is pressure differential. As long as the system is insulated from heat where the filter is should not matter. In this case atmospheric pressure is pushing the fuel to the pump,the filter is just part of the trip.
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Old 08-22-2010, 04:13 PM   #13
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Wink Re: Fuel filter: Before or after the fuel pump??

Quote:
Before or after the fuel pump?
I'm looking at my Holley Electric Fuel pump instructions and it say's before the pump.

I think I will take Holley's advice...I think they may have some experience in the matter.
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Old 08-22-2010, 04:16 PM   #14
39 All Ford
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Default Re: Fuel filter: Before or after the fuel pump??

When pressurized, a liquids boiling point is raised, (like a pressure radiator cap).

It only stands to reason that when suction is placed on a liquid, the boiling point is reduced.

Toms point is that a flow restriction imposed by a clogged, overly restrictive, or undersized filter would cause reduced pressure between the pump and the filter and make the car more susceptible to vapor lock.

This may not ever play out in practice for some (or even most) cars, but in some instances I am sure it will ring true, especially with todays gas.

IMO common sense says screen before pump, filter after, another reason for this is that pumps make pressure more effectively than they draw fuel.

(Atmospheric pressure AND displacement apply to pump theory).
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Old 08-22-2010, 04:19 PM   #15
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Default Re: Fuel filter: Before or after the fuel pump??

Quote:
Originally Posted by superiorslots View Post
I'm looking at my Holley Electric Fuel pump instructions and it say's before the pump.

I think I will take Holley's advice...I think they may have some experience in the matter.
Holley is trying to avoid warranty issues created when a piece of debris takes out their vane pump, this is "their problem", vapor lock is YOUR problem... things ain't always as they seem.

Detroit uses a screen before the pump and a filter after, both a blown pump AND vapor lock issues are "their problem" under warranty.
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Old 08-22-2010, 04:28 PM   #16
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Default Re: Fuel filter: Before or after the fuel pump??

I have always run a filter before and after the pump , mechanical or electric , in addition to a manual electrical cut off for the electrical pump , Mainly for saftey in case of a mishap or accident and it also works secondly as an anti-theft device, thief can't go far on a carb bowl of fuel.
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Old 08-22-2010, 05:06 PM   #17
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Default Re: Fuel filter: Before or after the fuel pump??

Most cars have a sock filter in the tank to take care of the big stuff. If I'm building a project I always replace this "sock" filter. Then if I'm running an electic pump I install a high flow filter BEFORE the pump and a high flow inline after the mechanical pump/ before the carb/s. On a drag car use one of the large capacity Fram filters right out of the tank and before the electric pump.

Frank
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Old 08-22-2010, 05:08 PM   #18
dirty old man
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Default Re: Fuel filter: Before or after the fuel pump??

Carter also voids the warranty on their electric pumps without a filter before pump. I've set mine up with an AFCO stainless prefilter capable of handling race cars on methanol, 100 GPH @100 micron, then carter pump, then Fram HP-1 with replaceable paper pack filter, 90 GP @ 5 microns,then Holley pressure regulator, and then 2-500cfm Edelbrock 4bbls.
Holley
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Old 08-22-2010, 05:55 PM   #19
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Default Re: Fuel filter: Before or after the fuel pump??

I bought a small 12 Volt Carter replacement electric fuel pump from Car Quest a few years back. Sort of a universal fit type. 5 or 6 pounds of pressure. It had a small fuel filter built into the pump. It was on the side the fuel entered. They sold replacements for the filter also. I replaced the filter about every 4 or 5 thousand miles ... because I had a 60 year old fuel tank that to my knowledge had NEVER been out of the vehicle.

Never had a problem ...

I also had a small A/C brand fuel filter at the carb.

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Old 08-22-2010, 06:05 PM   #20
57JoeFoMoPar
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Default Re: Fuel filter: Before or after the fuel pump??

I've always run a filter before the pump, and generally one before the carb too. I have a Holley Blue mounted next to the tank, and a Fram canister style filter before it, then an in-line filter under the hood. Been thousands of thousands of miles with no fuel delivery issues with that configuration
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