/3rd Gen RX-7 Fuel Reservoir/

Many road racers have complained about the stock fuel tank for the 3rd Gen RX-7. The poor design of the fuel tank is prone to fuel starvation upon hard cornering on the race track. Getting a racing fuel tank to have the pick up line directly at the bottom of the tank seems to be the only option but making such a modification is not an option due to the cost of the modification. Now I am making a fuel reservoir that runs between the stock location fuel pump and the fuel rail. With an assistance of an external fuel pump, the fuel starvation problem can be prevented. 

This idea is not original.  It has been practiced in Japan by numerous Japanese RX-7 tuners such as RE Amemiya, FEED, Top Fuel, R-Magic, RE Wing, Revolution Motorsports, C-West, Knight Sports, etc, on race tracks.  Getting one from Japan is just not economical and technical support is not going to be there.  No shops or RX-7 tuners I know of carry this kind of product so I am going to manufacture a few of these units to help out the RX-7 road racers to solve the fuel starvation problem.  The photos below show our custom fuel reservoir with -AN6 fittings for stock fuel pick up assembly.

How it works:

You need to keep the stock fuel pump for fuel  pick up.  The outlet of the fuel pump will be feeding fuel to the reservoir from the top.  The external fuel pump will deliver the fuel from the reservoir to the original steel line that goes to the fuel rail.  There is absolutely no cutting to the stock system.  You do not even have to open the fuel pick up assembly to install this fuel reservoir.  If you do not understand how a basic fuel system works, read on...

1. Stock System: A basic fuel system has a few components: fuel tank, fuel pump, fuel pressure regulator (FRP), fuel rail, injectors, fuel return line.  There is a high pressure zone and low pressure zone on the fuel system.  On a stock system, the fuel pick up point of the fuel pump is the low pressure zone. The other end of the fuel pump is the high pressure zone.  The fuel pressure is controlled by a FRP.  After the FRP is the fuel rail where the fuel injectors are mounted.  After the fuel rail is the fuel return line which returns the unused fuel back to the fuel tank.  

2. Reservoir System:  The reservoir is added between the fuel pressure regulator and the high pressure side of the stock fuel pump.  A external fuel pump is added to deliver the fuel to the fuel rail.  (Please refer to diagram 2 and 3) The design of the fuel reservoir is the one shown on the diagrams with 3 fittings on the top and at least 1 fittings at the bottom.  The number of fittings on the bottom varies with how many external fuel pumps you are using.  The stock fuel pump is acting as a fuel pick up pump which delivers fuel to the fuel reservoir.  One thing very important to understand is that since the fuel return line that is mounted from the reservoir to the fuel tank, the high pressure side of the stock fuel pump is not at high pressure anymore because the pressure is relieved through the fuel return line.  What's the effect of this?

• The stock pump will flow more than it used to.  Since the fuel pressure at that section is close to 0-10 psi due to the pressure relief through the fuel return line between the reservoir and the fuel tank, the fuel pump will flow a lot more than it used to at  the pressure of 40 psi + boost pressure.  Fuel pumps flow less at high pressure.  For Example, the Walbro High Pressure 255 L/H pump flows 80 GPH at 0 psi, 60 GPH at 40 psi, and 50 GPH at 55 psi (boost @ 15 psi).  People who worry that the stock pump cannot keep up with the external fuel pump and cause the fuel reservoir to run dry  do not understand this concept of fuel  pressure vs. fuel flow and also the pressure zone changing before and after the installation of the fuel reservoir.

To figure out which external fuel pump will out flow your stock pump, you have to compare the flow rate of the stock pump at 0-10 psi to the flow rate of the external fuel pump at 40 psi.  The higher your boost pressure the better because your stock fuel pump will always flows at 0-10 psi no matter how much your boost is.  But the higher the boost, the lower the flow rate of your external fuel pump.  If your still not convinced, or still feel unsafe, just use the same pump with the same flow rate for both the external and stock location.  The stock location one will always flow more than the external one.    

Another way to look at it is to determine the stock fuel pump flow rate at 0-10 psi and see if your fuel requirement will exceed that amount.  Even if the external pump flows more than the stock pump, the excess unused fuel will be returned back to the reservoir.  See diagram 2 and 3.  You will never run out of fuel as long as your stock fuel pump can flow enough to keep up with your fuel requirement. 

FAQ:

1. Will my stock pump keep up with the external fuel pump or will the reservoir run dry? 

See Above Explanation.

2. Where does the extra fuel go to? 

Study the diagram carefully.  Follow the direction of the fuel flow and you will see the extra fuel will return back to the fuel tank.

3. Will the reservoir over flow and / or will the pressure build up and burst? 

 The fuel reservoir is the low pressure zone of the fuel system?  Please read How It Works section again and study the diagrams really hard.  The only one condition that will make the pressure build up is a too small of the fuel return line going from the reservoir to the fuel tank.

4.  Do I have to install the fuel reservoir inside the trunk like shown in the photos?

 You do not have to.  You can also mount it inside the compartment behind the seat.  You can also mount it on the driver side of the fuel tank if you make your own custom bracket. You can even mount it inside the fuel tank but if you go that route, it's probably easier for you to go another approach by replacing the stock fuel tank with a race fuel cell,  have some baffles welded inside the tank or use the in-tank surge tank.  The fuel reservoir is universal.  You can put it on any car and anywhere.  It does not matter if it sits above the fuel tank or below the fuel tank as long as you do not mount the fuel reservoir upside down.  You should always mount it perpendicular to the ground with 3 fittings on top and at least one fittings at the bottom.  

5.  How loud is the external pump?

  You can use foam around the pump like photo #2 to dampen the sound.  You can  make a custom box with dynamat around the walls and put the ext. fuel pump inside the box to reduce the sound.  You can do a lot of things to reduce the sound of the external fuel pump.  Your exhaust is probably louder than your stereo by the time you need this thing. 

6. Why not use baffles inside the fuel tank, a in-tank surge tank or race fuel cell? 

   All those require you to take off the fuel tank.  All three require welding or at least some kind of modifications to the fuel tank.  Our approach with the fuel reservoir is the easiest one. Anyone can do it with simple tools.  There is no modification to any of the stock fuel component.  You can put everything back to stock if you want.  You can use this system just for track use and return everything back to stock after your track event.  

7.  Is it safe to put it inside the trunk and use it on the street?

  This kit is for track use, not for street use.  You do not need to make tight turns on the street and you are not supposed to.  If you decide to use it on the street, you can but it's your choice.  Is it safe?  It's a hard question to answer.  Is it safe to have a NOS bottle in the truck area?   It's a question similar to that.  It's all up to how you use it and how you install it.  Anything fuel related is not safe 100%.  Track racing is not safe.  Nothing is safe 100%. We cannot answer your question but we can only say that the components of the kit are top quality.  The thickness of the tank is closed to 1/4".  The fittings are Earl's fittings.  The lines are Earl's SS braided lines. You also have an option to mount it outside of the car on the drivers side of the fuel tank.  The fuel reservoir is universal and you can install it anywhere and on any car.  You do not want to mount it inside the trunk, you can mount it somewhere else with enough space.

8.  Can I run more than one ext. fuel pump? 

 Yes, you can run as many fuel pumps as you want by adding more fittings to the bottom of the fuel reservoir for fuel pick up for the external fuel pumps, assuming the pump you use in the fuel tank can provide enough fuel at 0-10 psi to match the total flow rate of your external pumps at 40 psi fuel pressure.

9.  How to install it?

  Refer to photo #1.  The picture is pretty self-explanatory.  Also study diagram 2 and 3.  

Capacity:

The fuel reservoir will have a volume of approx 1.5 liter.  Most aftermarket high flow fuel pump flows at 255 liter/hour.  You can convert the unit and the flow rate is  0.071 liter/sec.  If the fuel reservoir is 1.5 liter and the fuel pump is flowing at full capacity at 255 liter/hour or 0.051 liter/sec, the fuel reservoir can support 21 sec of fuel without the stock location pump supplying any additional fuel during the fuel starvation period.  This buffering period should be enough for any kinds of corners on any kinds of track.  If you want a larger reservoir, it can be custom made.  E-mail rotary_extreme@hotmail.com and get a quote on a custom size or custom style fuel reservoir. 

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