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.
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 delivery 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...
Stock Fuel System (1)
and one external fuel pump (2)
With reservoir and
two external fuel pumps (3)
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 are 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. Tthe 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 has to be 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 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?
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 you 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 flows more than the external one.
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 fuel will be back to the fuel tank.
3. Will the reservoir over flow and the pressure built up and burst? Hmmm... I will be very pissed if you are asking this question. Don't you know by now 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 builds up is a too small of the fuel return line going from the reservoir to the fuel tank. I do not think it will happen on our car if you use the stock fuel pump for pick up or even a 255 l/h high pressure fuel pump. Think really hard and you will know why. If you still do not know why, I will tell you under one condition, when you place an order with me so you can use money to avoid the thinking process. =P
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 of 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? How loud is too loud. I do not know. You can use foarm 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. But if you need this setup, I will think you are man enough to take tight corners at high speed but you worry about the sound level of an ext. fuel pump? Things just do add up right together don't you think? 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. My 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? I am making this kit 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 fueln