fuel return

phunk

In short, the purpose of a return fuel system is to regulate fuel pressure at the rails, rather than at the pump. This provides more stable and consistent fuel pressure as it remains under better control.

Explained; There is a fuel pressure drop that occurs across the fuel line. The longer the line, the smaller the line, or the greater the flow; the more pressure drop across a fuel line. At stock power levels, the flow through the stock fuel line is minimal as the fuel flow matches fuel consumption and low horsepower means low fuel consumption.

As power increases, fuel flow increases, and this causes pressure to drop. With a stock returnless system, you are regulating fuel pump pressure, but not rail pressure. Your rail pressure result will be pump pressure minus your feed line pressure drop, which increases as power/flow increases. Your pump is always capped off at 52psi by the stock regulator.

The reason for a return system is to regulate pressure at the engine, which is more consistent and reliable. Now your fuel rail pressure will be consistently controlled by the regulator (opposed to variable pressure drop), and the line pressure drop in the fuel feed line will be absorbed by the fuel pump. So if you want 52psi in the rails, the pump can operate at rail pressure plus line pressure drop for a total higher pressure to accommodate the end result of ideal rail pressure.

A return fuel system like the CJM system benefits you from a few things... For 1, most obvious, it is a return system, so you are regulating rail pressure rather than pump pressure. 2, you have increased fuel feed line size, which reduces the overall pressure drop to begin with, and helps utilize the peak capabilities of the fuel pump. 3, an inline fuel filter allows you to bypass the stock one, and for use with E85 this is beneficial as the stock cellulose fuel filter will swell with moisture introduced by E85 and more quickly become a larger source of pressure drop. 4, the provided adjustable regulator has a vacuum port for if you or your tuner wish to change from a static fuel rail pressure to a 1:1 pressure.. this means the rail pressure will be a constant differential from the intake manifold pressure, which makes better use of the fuel injectors.

For the surge canister stuff mentioned above... that is about protecting you from sharp and sudden pressure drops as a result of fuel pump starvation caused by fuel sloshing about in the tank. These products and this fuel slosh issue is, for the most part, entirely unrelated to return fuel systems. Surge tanks have been around forever, and you can use them with or without return fuel systems. Surge tanks allow a returnless or a return fuel system to continue to function properly when the fuel inside the tank sloshes around during extreme driving.


Questions answered:
fuel retrn is must for e85 : No.
does fuel return necessary for 93? : No.
does fuel return necessary for turbo 93? : No.
will the engine more reliable without it? : No.
does GTR come with fuel return? : Yes

A return system is never required, you can always work without it. As your fuel consumption/flow increase, you become better and better off to have one.

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chendaxian888

Got it! very good answer!

THE BULL

Wouldnt a 2 liter surge tank with a 6-8 AN hose that feeds the rails help with volume and pressure?

As the engine demands more volume, wouldn't then this volume be satisfied being that there is already 2 liter of pressurized fuel in the surge that can be refilled by the pump once WOT even has ended?

phunk

A surge tank with its own fuel pump(s) providing the rails with pressure reduces or eliminates fuel slosh starvation. If you were to also run a larger fuel line from the surge tank to the rails, you could reduce the pressure drop between the surge tank and the rails. You do need to regulate the new system though, and you do need to devise a technique to keep the original in-tank venturi system operational, since plumbing the stock fuel pump module to fill a surge canister would relieve the original sending unit from pressure thus eliminating the backpressure required to keep the venturis working. If you are adding a new fuel line from the surge tank to the rails anyway, seems like youd be best off to just put the new regulator in the engine bay as you will now have 2 fuel lines and thus can also have a return system, killing 2 birds with one stone. There are ways to make surge canisters work in vehicles with backpressure venturis, but it is a little overcomplicated and that can make it finicky and depend on installation conditions that can become a hassle in certain applications. This is why, for our product line, we eventually strayed away from this overly complex arrangement. We ended up solving all the fuel slosh starvation issues directly at the primary fuel sending unit in the fuel tank, with no secondary fuel system required. We do still call it a surge tank, but it actually just replaces the original fuel sending unit and the entire venturi system. We did the separate surge canister thing for like 10 years, and while it works for the majority of customers, it also painted some of them into a corner when they needed to make custom changes.

To answer your question in short: Yes, a surge tank with a big feed line to the rails can solve issues. But unfortunately the integration is more complex than it sounds and can be finicky with the backpressure side venturi system the Z uses. I wouldnt generally recommend this route to someone unless they have a strong understanding of fuel system dynamics so that they know what they are up against and how to sort out the less obvious issues when encountered. But sure, if you set it up right and dial it in, it could very possibly handle your needs.

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avioni

questions.

does the external regulator on a return system go before or after the fuel rail? if after then how is that installed with oem fuel rails? if before how does it work?

is the fuel dampener connected to the rubber hose that goes to the firewall needed? i have an issue where the dampener line hits the throttle cause of stillen plenum and i bent the line down and it kinked a bit. solution would be to install a plate with AN fitting replacing the dampener and a line to the firewall. but 2 reasons why i havent done it. dont know if the dampener is required and cant find anyone selling a line that would clip to the firewall line and have an AN fitting on the other end.