Return vs Returnless Fuel System

[NovaDude]

I'm planning a Sniper EFI install for my '69 Nova. I need to decide to go with either a return style fuel system (PN 19-165) which requires a new tank (costs more) or a returnless retrofit system (PN 12-300). With a return style system, fuel pressure will always be regulated to a consistent pressure at the fuel rail. With the returnless style, the fuel pressure is regulated at the pump in the tank, so when there is high fuel flow, pressure drop through the line will go up, reducing the pressure at the fuel rail, and thus the flow rate through the injectors, causing a lean condition. My understanding from emailing Holley tech and Chris at EFISystemPro.com is that with a returnless system the Sniper ECU relies on the WBO2 sensor to sense a lean condition and then increases the injector pulse width to compensate.

To make matters worse, at low load and fuel flow, such as at idle, the engine will be under vacuum. So if the fuel rail is at 60psig (74.5 psia) and the intake manifold is at 7.3 psia (15 in Hg), the delta pressure across the injector, which is what determines flowrate, is about 67.2 psi. When the engine goes WOT, fuel flow goes up, increasing pressure drop, the manifold pressure also increases. If we get 14.5 psia manifold pressure, and let's say 3 psi of pressure drop, we are at 71.5 psia at the fuel rail, for a delta pressure of 57 psi across the injectors.

My question is has anyone run the returnless style fuel system with the Sniper EFI? Any poor running or lean out at high load, such as flooring the throttle from idle? Anyone have experience running both of these fuel systems that can compare the performance? I know the OEMs use a returnless style, but in that case the pumps are usually pulse width modulated to increase pump speed as fuel demand goes up, which is not the case with the Holley retrofit system.

[81 TransAm]

I run a returnless fuel system. My regulator is in the fuel basket in the tank. Then a single line to the front. I'm in the 450 HP range and I don't experience any flow issues. At WOT, I lose about 2 to 3 lbs of fuel pressure. But that could be in the efficiency of the regulator. I've used both methods and didn't notice any difference between them. The reason I went this route was to reduce the heat in the fuel tank. The return line was picking up heat in the engine bay and after a couple hours of driving, my tank was getting real hot.

[NovaDude]

So after talking to Holley tech support, they explained that because the Sniper is TBI, the injectors are above the throttle, and don't see manifold pressure. The only deference between the two then is pressure drop in the line at high flow rate.

81 TransAm, what caused you to notice the tank getting hot, did it cause any issues? Having a hard time figuring out the right way to go, the Holley tech I talked to said he never recommends a returnless system for a street car because it is more prone to fuel boiling.

[81 TransAm]

I was using external pump & regulator and getting fuel boiling. Going internal & return less solved my problem. How well would it work with higher HP levels, I don't know.

[Gen2Van]

I was using external pump & regulator and getting fuel boiling. Going internal & return less solved my problem. How well would it work with higher HP levels, I don't know.

Now I know why you suspected pump cavitation in my thread on the Sniper forum. I'm running a HyperFuel G-Surge 40009 unit, which is basically a pump and regulator self contained in its own housing with 1 liter of fuel contained within. It's built very nice. I'm feeding it with an unregulated Holley blue pump and a return line from the HyperFuel to the tank. The pressure out is deadheaded to the EFI.

Recently I began having random engine stalling issues with no real reason. I suspected spark at first, but I rewired & replaced all my ignition components with new. Problem came back. Now I'm looking at the fuel system. I haven't had good luck running a returnless system from the EFI.