Sequential Dual Fuel System - 1978 Malibu



Fully Automatic Switching Dual Fuel System

     This is the dual fuel system I made for my turbocharged 1978 Malibu. It's a system that does not allow mixing of fuels commonly found in dual fuel systems. It can be fabricated to work on ALL engine's regardless of the engine size. Here you will see how it all works together. This project was fabricated in 2005-2006 and is still in working order and works flawlessly even today! Jan 2012.


     What if you could have a turbocharged or supercharged car that you could cruise around on the street with lower priced 87 octane and at the same time you could also have 116 octane ONLY WHEN UNDER BOOST? Sounds almost to good to be true! Well, years ago I had an idea of having two separate fuel systems; one for 87 octane and one for 116 octane. I wanted something that switched immediately; such as "in a blink of an eye". The only way to achieve immediate switching is to have two sets of injectors located in the intake manifold. This would allow each set to be electrically switched by a relay. I didn't want a dual fuel system like pick-up trucks have that uses a mechanical switching valve on the fuel lines. The mechanical switching valve does not allow IMMEDIATE switching from 87 to 116. Mechanical switching also allowed the two fuels to mix together which would eventually dilute the 116 race gas and render it useless for high boosted engines.

      The Sequential Dual Fuel Injection (SDFI) will allow cruising around on 87 octane and still be able to run 20+ (or even 30+) pounds of boost at the same time! This will also eliminate having to drain the fuel tank and fill it up with high octane gas before going racing; then having to drain it again to put low octane back in for cruising around. This will also save money on fuel costs since the car doesn't have to use expensive race fuel for everyday commuting. In fact, it will save me 20 cents per gallon over 93 octane since I can use 87 octane to power the car under normal operating conditions. I figured I can save $3.40 for every 17 gallons of fuel used. That isn't much of a savings but it adds up every time I fill up!

      Another major bonus is it will conserve race fuel since it will be used only when needed. How many times have you put expensive race fuel in your car only to burn the majority of it out cruising to and from your favorite tuning spot or your local drag strip? If you timed how long you are actually running the car under high boost conditions it would probably add up to 10 to 15 seconds at a time. 5 gallons of 116 race fuel will last a lot longer when it's only being injected a few seconds at a time. This system operates just like I thought it should!! In my opinion, it doesn't get any better than this! Read on and let me explain how this system actually became a reality!


Key things to remember:

1. No fuel mixing
2. No delay in getting race fuel into the cylinder.
3. Lengthens the life of O2 sensors due to leaded fuel not being used as often.
4. Conserves race fuel because you only use it when you nail the throttle.


     So, I know by now you want to SEE how it operates on the car. I've provided a video for you to see it in action. In this video, I have the both injectors unplugged on cylinder #3 so the engine will be missing on that cylinder. The top noid light is for 87 octane and the bottom is for 116. I am switching them MANUALLY in this video. Listen at the tone of the engine while looking at the noid lights. Watch how the fuel system switches with the engine under load. See if you can hear when the injectors "switch" over from 87 octane to 116....listen closely!

Click here to download a video of it being tested on the car or take a look at it below.



     This system uses two injectors per cylinder and does not allow the fuels to mix when switching from low octane to high octane. Having a fuel line switching valve on the car will ALWAYS mix the fuel no matter how close you have the switching valve to the fuel rails. I've eliminated the mixing by using two completely separate fuel systems. There's NO OTHER WAY of doing a dual fuel system without the fuels mixing together!

Click on pictures to enlarge:




Now that you understand what's going on here, this is how I have the fuel injectors wired.


Fuel injector wiring:

     The "injector power feed wire" from the injector fuse is routed through a dual contact/5 terminal relay. This relay is does the "switching" when boost reaches a predetermined level set by the boost activated switch.. You can see in the wiring diagram that only one set of injectors are powered on when the engine is running. Once the boost activated switch reaches the desired boost level it grounds the relay and power is then routed to the other set of injectors (116) while it turns off the other set (87). Once the boost level is above the "set" point of the pressure switch, the race fuel is begins to be injected in the engine. After you let off the throttle, the boost drops below the "set" point of the boost pressure switch and then the power from the 116 injectors is returned to the 87 injectors. The engine will now be running on low octane fuel for cruising. If you don't want the system to operate in automatic switching mode all you have to do is to remove the boost pressure switch and install a manual toggle switch...BUT watch out when doing might forget to flip the switch and when the engine gets into high boost on 87's dead.  This system DOES NOT KNOW WHAT BOOST LEVEL YOU ARE RUNNING so I'd recommend always having it set up in automatic mode...just to be safe.

Dual Fuel System Wiring Diagram


Fuel pump wiring:

I have THREE fuel pumps in my car. One is located in the stock fuel tank and the other two are in the fuel cell. With this system, two fuel pumps run anytime the engine is running. One runs in the 87 octane fuel tank and one runs in the 116 octane tank. This way, both fuel rails are already primed up to pressure when the system switches over to race fuel. For lower performing cars that don't need "double pumpers", only one fuel pump is needed in each tank. On higher HP cars (like my Malibu), I have "double pumpers". The second pump turns on at low boost...3psi or less. This will ensure that once the boost reaches high enough for the fuel system to switch over, there will be enough pressure and enough volume there when the engine reaches high boost. It's really a very simple design when looking at it on paper but it's complicated and expensive when it comes to fabricating it. As the saying goes...."If you're gonna have to pay!".

Dual Fuel System Fuel Pump Wiring Diagram














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