Originally Posted by 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.