MR2 Center-Feed Fuel Rail Installation: Overview

Fuel Pump	Fuel Rail	Fuel Pressure Regulator	Parts List

The stock second generation 3S-GTE fuel system can support a maximum of 275 to 280rwhp. The modification described here should be capable of supporting 500rwhp with 850cc side feed fuel injectors and a Twin Turbo Supra fuel pump. There is no reason to perform this or any other fuel rail modification if the stock injectors are to be used, so this fuel rail modification should be considered only to support larger fuel injectors. An upgraded fuel system requires an appropriate EMS to properly control the fueling and ignition timing of the engine. Do not use an AFC with the stock ECU or a G-Force/Techtom  ECU to control a high-power fuel system without appropriate timing controls. The AFM signal alterations that these devices use to adjust fueling also advances timing to dangerous levels. A single blown engine will cost more to rebuild than a good EMS will set you back and some people have blown their engine more than once using poor fuel control.

Dual feed fuel rail modifications are fairly common on MR2s to handle the increased fuel flow that the rail must supply when four larger fuel injectors are used. There is a myth that the stock fuel rail needs to be bored even with stock injectors because it does not supply enough fuel to the injectors, but this is really a drawback in the design of the intake manifold which tend to supply more air to the middle cylinders than it does the end cylinders. The modified fuel system described here is similar except that a single feed is used. The stock fuel rail is fed from the #1 cylinder side of the fuel rail. In the middle of the fuel rail, there is a tap for the cold start injector. At the other end of the fuel rail, the stock fuel pressure regulator regulates the fuel pressure inside the rail and allows unused fuel to return to the gas tank. Most dual feed fuel rails use a tee to split the incoming fuel into two feeds for each end of the fuel rail and a smaller feed to the cold start injector if needed. The unused fuel escapes from the fuel rail via the center tap which normally feeds the cold start injector. The center-feed fuel rail described here eliminates the cold start injector system which not needed when using an EMS that can be programmed to feed the engine extra starting fuel through the main injectors. The unused fuel exits from both ends of the fuel rail and regulated by an Aeromotive adjustable fuel pressure regulator with dual input ports. Because the center- feed rail feeds only two injectors on either side of the middle tap, the stock fuel rail does not need to be bored to handle fuel injectors up to twice the size of the stock injectors.

An alternative to the center-feed or dual-feed stock fuel rail is to get a top-feed fuel rail that can be used with more common and less expensive top feed fuel injectors. If your fuel needs surpass the requirements of the 850cc side feed injectors that are available, then either a top-feed fuel rail or a second fuel rail with an extra set of staged fuel injectors must be used.

Essential to upgrading the fuel system to its greater capacity is replacing the stock fuel pump with the higher flowing pump from the 1993+ Twin Turbo Supra. This is true even if only upgrading to the 540cc Supra injectors. The stock fuel pump is not capable of supplying sufficient fuel to keep four 540cc injectors fed above 300rwhp if running 20psi boost pressure (although it will support a little bit more if you can make 300rwhp at or below 15psi), so just upgrading the fuel rail and the injectors without addressing the fuel pump is a waste of time and money. This higher flowing Supra fuel pump is the same size as the stock fuel pump and fits the stock bracket inside the gas tank. Also essential  is an adjustable fuel pressure regulator allowing higher than stock fuel pressure so that each injector can supply a greater amount of fuel.

The stock fuel injectors are rated at 440cc. Larger side feed injectors are available from various manufacturers at various sizes up to nearly 1000cc. A rule-of-thumb formula for determining how much power you can push a well tuned 3S-GTE on a set of fuel injectors is:

Max rwhp = 4 x (Injector size cc / 5.8)

This formula will put you right on the edge with a base fuel pressure of 43psi, so it would be a good idea to only go to no more than 85% of this before upgrading the injectors. 550cc injectors can safely support 330rwhp and are a logical first step when upgrading the fuel system.

Modifying your fuel system is not a street legal option in most states. If properly done and controlled, a larger fuel system will not affect the vehicles emissions. There are limits and at some point larger injectors may make it difficult to get the engine to idle without being overly rich. If very large injectors are used, you will most likely need to run an EMS in fully sequential mode to pass emissions.

It is always a good idea to disconnect your battery and to keep a fire extinguisher nearby when working on the fuel system. Teflon tape is available in any hardware store and makes leak-proof threaded connections when properly applied. After working on the fuel system, never start the engine until you have performed a fuel system pressure test by connecting the +B and FP holes in the "Diagnosis" box with a heavy gauge wire or paper clip and turning the ignition key to "ON." This will run the fuel pump and bring the fuel system up to pressure without the engine running. Take a couple minutes to check and recheck for fuel leaks before starting the engine.