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Mechanical vs electrical fuel pump

 
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Old 12-27-2012, 08:58 PM
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Mechanical vs electrical fuel pump

Well the truck rebuild continues on my 81 150 4x4 and now I hit another question that I need help in. Should I opt for an electrical fuel pump or a mechanical fuel pump. Its a got a new summit racing 600cfm carb in there.
 
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Old 12-27-2012, 09:09 PM
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I wouldn't use an electric on that application unless I had a compelling reason to (and I can't think of any such reason based on the information provided in the question).
 
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Old 12-28-2012, 09:04 AM
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I'd go mechanical as long as you have the timing cover with the spot for it and the eccentric on the camshaft.
 
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Old 12-28-2012, 10:54 AM
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Originally Posted by bashby View Post
I'd go mechanical as long as you have the timing cover with the spot for it and the eccentric on the camshaft.
Why is the timing cover important?
 
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Old 12-28-2012, 11:15 AM
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That's where the fuel pump mounts on V8's. What engine do you have?
 
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Old 12-28-2012, 11:27 AM
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One reason to use an electric pump is that a mechanical pump has to "pull" the fuel from the back of the truck (tank) to the front of engine (pump). An electric pump (mounted at/near the tank as it should be) pushes the fuel. It is always preferable to push fuel.
Another reason some prefer not use a mechanical pump is that if the pump diaphram leaks, the some of the fuel goes into the cranckcase diluting the oil. If the leak is small enough it can go unnoticed until the oil is sufficiently diluted to cause engine (bearings, piston scuffing, etc.) problems.
 
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Old 12-28-2012, 11:46 AM
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Originally Posted by CountryBumkin View Post
One reason to use an electric pump is that a mechanical pump has to "pull" the fuel from the back of the truck (tank) to the front of engine (pump). An electric pump (mounted at/near the tank as it should be) pushes the fuel. It is always preferable to push fuel.
I would have to disagree with this. There is a reason that our helicopters have engine driven fuel pumps as a primary. Yes they have in tanks at low psi to get it to the lines but the engine is based off a suction type to prevent fuel flow in an event where there is a line leak. The same would apply that it would be better to suck air and have the engine die than to spray fuel at high pressure. Also by the using a mechanical pump attached to the motor allows the pump to correspond to the needs of the engine. Higher rpm more pumps and vice versa instead of having more pressure in the line than is needed with a high pressure constant which is not needed in a engine or turbine for that matter.

Not trying to debate just giving my two pennies as everyone has there own opinions and vehicles went to electric in fuel injection for some reason even though they didnt need to so you may be correct.
 
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Old 12-28-2012, 12:01 PM
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I've found that an electric fuel pump doesn't work well with a carb that isn't in top notch condition. I've had problems with electric fuel pumps forcing the needle off the seat in a carb and pushing fuel right past it. If you're going to use an elcetric fuel pump on an older carbed motor, I would use a pressure regulator to try and avoid such problems..
 
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Old 12-28-2012, 12:22 PM
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Originally Posted by EL_JEFE32 View Post
I would have to disagree with this. There is a reason that our helicopters have engine driven fuel pumps as a primary. Yes they have in tanks at low psi to get it to the lines but the engine is based off a suction type to prevent fuel flow in an event where there is a line leak. The same would apply that it would be better to suck air and have the engine die than to spray fuel at high pressure. Also by the using a mechanical pump attached to the motor allows the pump to correspond to the needs of the engine. Higher rpm more pumps and vice versa instead of having more pressure in the line than is needed with a high pressure constant which is not needed in a engine or turbine for that matter.

Not trying to debate just giving my two pennies as everyone has there own opinions and vehicles went to electric in fuel injection for some reason even though they didnt need to so you may be correct.
A Helicopter is a different animal. But I don't think I would be a happy flyer if the engine suddenly shut off due to "sucking air" - nor would I want fuel spraying on a hot manifold. I suppose the engineers know which is better.
Carburated gasoline engines are prone to vapor lock. It usually occurs on the suction side where fuel pressure is low. The longer the suction side/line the more prone to vapor lock (especially in hotter climates). Pressurizing the fuel line reduces the chance of vapor lock.

Most "street application" electric fuel pumps, such as the Holley Red pumps, have a built in pressure regulator. If the pump you are using over-powers the needle/seat, you are using an electric pump that requires an external regulator, such as a Holley Black pump, (or you have something setup wrong, or a faulty component).
See Vapor lock - Wikipedia, the free encyclopedia
 
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Old 12-28-2012, 12:51 PM
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It can get complicated.

Manufacturers did go to electric fuel pumps, but most are in the tank submersed in the gasoline. The gas keeps the pump cool, and the pump is in almost the lowest location it can be, to pick the fuel up. Like was said, they have fuel pressure regulators VERY NEAR THE POINT OF USE AT THE ENGINE which works a lot better than a regulator built into a externally mounted pump that regulates the fuel pressure down way back at the tank.

The pushing fuel instead of sucking it all the way up front is a valid point and works to avoid vapor lock like was said. It was mentioned there is a safety problem doing this, and Ford recognized this when they started using this system. On some engines Ford used engine oil pressure and a pendulum type safety switch to kill the pump in case of a accident. Later on they still used the pendulum safety switch and also used the engine computer as a interlock. If the computer loses signals from the distributor, it assumes the engine has quit and turns off the relay that controls the pump.
 
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Old 12-28-2012, 01:45 PM
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Yeah I see how it would prevent vapor lock and with safety systems in place they remedied the problems. I was just trying to make a comparison between the two with some pros and cons. I on a personal note would rather have the mechanical pump with a carb. Good points though guys.
 
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Old 12-28-2012, 07:35 PM
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I wouldn't use an electric pump if I had the ability to use a mechanical one. I've seen way too many people on here having problems with electric pumps, and very few people having problems with mechanical ones. In fact, if I had an electric one and could change to mechanical I would do so post haste.
 
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Old 12-28-2012, 08:26 PM
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just had the third electric pump go bad on me in the last 5 years, and only 10000mi.
 
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Old 12-28-2012, 09:24 PM
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I too am a fan of the mechanical pump. some of the aftermarket pumps are rebuildable. I even bought amechanical "race pumps" pump for my capri that can handle the pressure for fuel injection with a change of springs in the regulator.

I would like to add that General Aviation planes (such as your typical cessna) have a mechanical pump, but also have an electric aux pump that you use on takeoff and landing and such. you know, since you mentioned a helicopter. however an engine loss isn't nearly as bad in a cessna as it is in a bell.
 
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Old 12-28-2012, 09:36 PM
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In my several million miles of driving over 53 years I've been stranded by one fuel pump - electric.
 
 
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