Question on return line size......

[Fuelie Fan]

Everyone's a skeptic.



I don't work for that company anymore, so I don't have the spreadsheets. Even if I did, would I go through hastle of hosting our results? Probably not. This site isn't that important. I'm just trying to help by telling you of my direct experience, and if you don't want to believe the one poster here who has ACTUALLY tested it, that's your thing.

But, to be a good sport, I'll try to summarize my results: We tested mainly TBI regulators, both aftermarket and integral GM throttle body regulators. Our setup had negligible restriction to begin with, and an inlet pressure setpoint of 11 psi. Introducing a 1-2 psi of restriction via an adjustable valve actually LOWERED the inlet pressure setpoint by "around" (I don't recall precisely) 1/2 to 3/4 psi. From there, additional return line restriction caused the pressure to gradually creep back to the original setpoint, reaching that point at approximately 9 psi of restriction. Beyond that, the inlet pressure increased linearly, such the inlet pressure = restriction pressure + ~2psi. For those of you who are unaware, 9 psi of restriction is a LOT. You'd only see it if your line was practically kinked.

Have you ever even seen a pump curve before? All a pump cares about is the pressure that it sees. How that pressure gets created is inconsequential.
On a related note, Pumps are most susceptible to damage from adverse INLET conditions. If there is one recommendation i could give, it's that you maintain your inlet like crazy. Keep the clamps tight to prevent air leaks, make sure you don't have any restrictions, and mount the pump as low as possible. Use a prefilter (not too restrictive, 40-100 micron) and service it often.

I'd have to think about the temperature issue, but my knee-jerk response is, if your return line is even remotely correct for size, the temperature input due to line friction is nowhere NEAR the heat input from the engine bay, exhaust, radiated from hot asphalt, etc. Now, if YOU have actual experience showing that you prematurely killed a pump or superheated the gas tank by running too small a return line, please share, otherwise I'm treating it as pure conjecture.