BLOWN85

Got a few questions that hopefully someone can answer. I am looking to upgrade my fuel lines to 1/2. I had a Mallory comp 140 pump installed late last year and I am have some fuel issues. 1st question is do you run the pump before or after the fuel/water seperator? It is currently run after the seperator. I would think that being the pump pushes rather than sucks, that it should be mounted after? Next question, is there enough meat on the filter to drill and tap the 3/8" NPT threads to 1/2"NPT?

niceguy

I'll jump in here first.

I ran mine before the F/W seperator, but only because that is how it was setup from the factory (with the mechanical pump).

1/2" line is not the same size as 1/2" NPT. If you actually look at the 3/8" npt inside diameter, it is not far off from a true 1/2" line size.

But ultimatley if you want the 1/2" NPT holes in the filter mount, I'd just buy a billet mount that already has them. They arent too expensive... like 85-90 bucks/ea.

BLOWN85

I am going to check the syphon tube in the tank tomorrow. I had it apart last season and I think the tube was 1/2" I.D. As far as the rest of the lines. I will change them out accomidate the rest of the system. Now with the f/w seperator, should I move it to where the elec. fuel pump is pushing or pulling through it? Right now, it is after the seperator.

DMOORE

Electric pumps do a better job of pushing, rather than pulling. I wouls install the F/W separator after the pump. I would still have a fuel filter in front of the pump to protect it. Also, mount the pump low along a stringer.


Darrell.

niceguy

x2

Young Performance

I never push fuel through a fuel filter for several reasons. First, the filter acts as a reservior for the pump to pull from. Secondly, I do not want pressurized fuel going through the filter. If it should develop a leak then it will fill the bilge with fuel. I am doing installs for customers and I do not want the liability. A faulty oring or water causing the filter to rust could very easily cause a leak. Remember, it is a water seperator and it will trap some water. An electric pump can make quite a bit of pressure before the regulator. A stock mechanical pump will only make about 5-6 psi of unregulated pressure.
Third, the filter will keep trash out of the pump. Yes, you can use a prefilter, but putting the seperator first eliminates the need for it. Hope this helps, Eddie.

BLOWN85

Thanks for the info Eddie. Do you think that the fuel system is adequte enough to support 700hp? Can you pull enough fuel to 2 carbs thru a 3/8" Line? From the reg. to the distribution block is a -8 line. Once it hits the dist. bock, I have pre-bent aluminum line to the carbs..( I believe it would be comperable to -6 to the carbs.) Thanks to all that posted on this. I have some good info so far!!

ACrooks69

iTrader: (1)

Be careful putting the filter befor the electric pump. It would be nice to find the micron filtration capability of the Merc filter. What we don't want to to is put to restrictive of a filter before the pump. Read this excert from Aeromotive's website, makes sense:

The filtration media to be used on the inlet side of an Aeromotive fuel pump may be no smaller than 100-micron and must have an element surface area of 60 square inches or more. Any filter element not meeting these criteria may fail to flow the full volume of the pump being used, resulting in cavitation at the pump inlet. Aeromotive fuel pumps are extremely efficient by design, allowing them to create high pressure on the outlet and high vacuum on the inlet side, if restricted. Cavitation can be to a pump like detonation is to an engine and occurs when the liquid being pumped reaches a temperature where it boils and becomes vapor. The temperature at which any liquid boils varies with pressure. Recall that water in a radiator is purposely pressurized to raise the boiling point. When was the last time your high pressure EFI system vapor locked? Keep in mind, as a pump pushes it has to pull. When a pump has to pull too hard acquiring fuel, a vacuum or low-pressure area develops at the inlet. The better and more efficient the pump is, the lower inlet pressure will fall. The boiling point of any liquid fuel in this low-pressure zone falls as well. With a highly efficient pump, inlet pressure can get so low that fuel will boil and the pump will cavitate at normal operating temperatures. Today’s ultra-high output engines require equally high efficiency fuel pumps. Failure to install them properly can be costly in two ways: First, during cavitation the engine may experience a momentary lean condition (losses of liquid fuel pressure and volume). Second, excess heat and friction will build in the pump, causing damage and eventual failure. If you feed your Aeromotive pump properly it will feed your beast for years to come! Review your installation and make sure the pump is mounted where gravity will help push fuel to the inlet, use the correct size AN line between the tank and the pump and install filters that flow the necessary volume freely.

I wonder if the way Merc has the return line going to the fuel filter assembly aids in reducing this?

niceguy

On low HP deals, it will probably be ok. But keep in mind most of the F/W seperators only flow a max of 100gph (at least the ones I found)... and most aftermarket electric pumps flow well over that.

The problem then becomes that the F/W sep becomes a restriction for high HP motors. But how high? In theory, you should have roughly 200+gph for 700hp.... but in the real world? I don't have that answer. Maybe some of the Engine builders will jump in here and give us some examples of what they have done in the past.

SDFever

I have an Aeromotive System (pump and regulator) and I did a simple test of the stock Mercury fuel filter manifold for a 496.

Verified 1/2 from tank with no anti-siphon valve and good load of fuel.

Everything staying the same EXCEPT the actual manifold for the spin on fuel filter. My stock one was 3/8 and my new one is the same style but with 1/2 feed and supply.

At solid 51LBS of fuel set by regulator, there was no difference. While using the stock manifold (3/8), i stopped the boat after a wot run and used a straight bypass butt type barb with zero restriction (1/2).

Then, installed the actual same style spin on manifold as the stock one but with 1/2 support. There was no difference what so ever going from 3/8 manifold to an actual filter by pass barb and then onto the final 1/2 spin on manifold.

Needless to say, my particular test was ONLY to verify the conditions of the fuel filter manifolds themselves and had nothing to do with rest of fuel delivery system test.

It's fairly interesting to me though because I would have assumed the two manifolds would be at least somewhat different.