Fuel pressure issues

padam

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I'm getting involved in drag racing again after about 20 years on the sidelines.

My car is a 73 Charger that was originally a 318 auto car I bought in 1981. In the 80's I modified it quite a bit:
413 with 906 heads, MP 484 lift cam.
Holley 750 vac sec, Torker intake, Holley blue pump.
MP orange box and distributer. Timing is about 38 total, no vacuum advance.
4-speed, 8-3/4 sure grip 4.30 ratio.

This combo worked pretty good before,
Used to run 12.50 at ,105 mph.
8:20 1/8. With slicks and open headers.

I took it out a couple times this year, running through the mufflers and on dot Hoosier tires.
It ran pretty crappy, sounded just as bad.

So I'm trying to fix a misfire condition at wide open throttle / high speed.
So far I have replaced plugs, wires, cap, and rotor.
Compression test was decent most 160psi, lowest 150 hi 170.

I finally installed a fuel pressure gauge I've had on the shelf for 20 years, and the pressure is good at 6 psi until I floor it then drops to under 3.
I disconnected the fuel line to change the Mallory filter, and the fuel just trickled out of the line.
I have fuel cell and some bits of the foam were in the filter.
It also looks like the foam was jamming up the outlet. See pic.
I pulled the foam out and it didn't look horrible, but obviously starting to degrade.
So I'd say 25 years is pushing the limits on fuel cell safety foam.

IMG_20200813_160239389.jpg
 

dvw

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The foam can get everywhere. Take the pump, regulator and, carb apart. Clean them all. Then either replace the foam or leave it out.
Doug
 

Frank Mopar

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The foam in a fuel cell is there for a reason. It keeps the tank too rich to blow up. Replace it and your good to go.
 

padam

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I'll probably replace it, although I see they sell new cells with or without foam.
I hate to remove a safety feature, especially related to fire.
 

dvw

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The foam is for slosh and to disperse return fuel flow preventing aeration. Baffling could do the same job but foam is cheaper. If it related to volume/fire a stock tank would have foam.
Doug
 

Frank Mopar

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The foam is for slosh and to disperse return fuel flow preventing aeration. Baffling could do the same job but foam is cheaper. If it related to volume/fire a stock tank would have foam.
Doug

Incorrect. If you take the foam out of a fuel cell it becomes a gas tank. The slosh part is a benefit but not the reason its in there
 

dvw

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Definition & Description
Fuel Cell Foam is a special, sponge-like material that is installed inside a racing fuel cell.

Fuel_Cell_Foam.jpg


The foam is mostly air, so it doesn’t reduce the capacity of the cell. However, it provides a few key benefits:

  • It reduces sloshing.
    • This reduces fuel aeration and improves fuel delivery.
    • It also helps with weight distribution and vehicle handling.
  • It occupies the free space inside the cell.
    • This prevents fuel vapor and air from concentrating.
    • In the event of a fire, this reduces the risk of an explosion.
  • In cells with a bladder, the foam holds its shape.
There is always fuel vapor in a tank. So in theory the foam takes up space that could be holding vapor. But there's way more room for vapor in a normal 30 gallon tank than there will ever be in a 5 gallon cell. Does that stop you from driving your pick up?
Doug
 
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padam

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Doesn't matter much to me now, pretty sure I trashed the motor yesterday.
 

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