Club Cobra - Fuel Pump Sizing

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Fuel Pump Sizing

Not being one to leave well enough alone...I installed a fuel press (smiths in a period correct aux mount under the dash -removeable with no tell tale with two screws) on my SPF.

I noticed that at big throttle settings that the fuel press was dropping WAYYY off (kinda hard when trying to keep the rear wheels in back of you and look down at the gauge).

I have a 30 GPH Carter hot dog arrangement right now, with a regulator set to 5PSI.

SO if the floats are dropping and admitting fuel to the bowls when the boosters are at full song, the pressure SHOULD go down to some extent i would think? How much?

The inter-web cites a fuel pump calc that takes HP x BSPH/constant= necessary GPH of fuel flow:
Using BSPH=0.5 for a NA motor, and a constant of 6 i get about 45 GPH, a healthy 50% over what ive got...

Doing the algebra, my little 30 GPH will eventually starve the motor at anything above about 288 HP (at the crank using a driveline loss of !0.8)...

On my motor this occurs at ~3000 RPM according to the dyno curve.

Im thinking i'd better get a better pump?

don't forget a good sized fuel line, 1/2"

The idea of a pressure regulator is to maintain a set pressure at the needle and seats.

So set at 5psi at idle, should still be 5 psi at 6000rpm.

When this doesn't occur, we have inadequate supply.

Fuel line too small, restrictive filters, pump too small etc etc.

Gary

Quote:

Originally Posted by FWB (Post 1441932)

don't forget a good sized fuel line, 1/2"

The hard tap out of the tank is 3/8", seems like any thing bigger downstream wouldn't matter?

I run a 100GPH Carter and i works very well feeding my 750CFM Holley. If you are going to continue using the hard 3/8" line (which probably is sufficient), there would be no real benefit to piecing in a short section of 1/2" line to either end of the hard line.

Quote:

Originally Posted by tortuga (Post 1441951)

The hard tap out of the tank is 3/8", seems like any thing bigger downstream wouldn't matter?

A frequent mistaken "truth".
The total resistance through a pipe (similar to resistance in a wiring circuit) is calculated by the sum of resistance through each component. While a single restriction in a pipe might be a major part of the total resistance, it's not the only one.
https://www.pipeflowcalculations.com...w-in-pipes.php