FULL FLOW RETURN FUEL SYSTEM
The 2006-2015 Mazda MX5 was built with a simple return-less fuel supply system. This works wonderfully in the stock car and will provide years of trouble free service. However, superchargers, turbochargers, or even high flowing normal atmospheric engines require more flow than the stock system can deliver. Over the years of our work with this platform, we have seen an increase in the demand for power from customers. To this end we are developing new products to solve some of the "flaws" built into the stock systems to allow that increase. The Full Flow Fuel System is one of those solutions!
The factory fuel system is a "deadhead" set up with the pump pushing fuel into a closed fuel injector rail that feeds the 4 injectors. Fuel is delivered to the fuel rail on one end, and allowed to fill the rail. This rail then feeds the injectors.The best way to think of the rail, in stock form, is as a pressurized tank feeding the injectors. On a stock car this design works well, and has zero issues. The rail, and flow are designed by Mazda to provide more than enough fuel for even the most performance driven stock 2.0.
As you increase the output of the engine, it requires more fuel for each cylinder. Since the rail ( pressurized tank) is a fixed volume, this means that each injector is drawing more volume from that reserve. So the available volume drops to each subsequent injector. In short, as you proceed down the line of injectors, each one is seeing less and less available fuel volume for it to inject. In our testing, we found that even low level increases in output (100-120 WHP) will cause the #4 injector to begin to "starve" for fuel. When you get to the really big output engines (400-450 WHP), the rear two injectors are running flat out of fuel!
As we have progressed towards higher and higher output engines, we always knew that this was a problem, and that one day we would need to address this issue. To that end, we undertook an extensive test to figure out a good solution. Our testing provided some surprising results. We first modified a stock fuel rail with pressure sensors after each injector port, and tested it on the dyno on a stock car. As we suspected, this system worked fine for the stock output engine, however, after testing on a 2.0 with an installed FMSC ( Flyin Miata Supercharger), we were amazed to see that there was a 10-15 drop in pressure at the #4 injector. This is 5.6- 8.4 lbs of fuel pressure that the rear cylinder is not seeing. This results in a lower volume of fuel being injected for the IPW (Injector Pulse Width), or the time the ECU opens the injector.
When you get to the big boys of output (350-450 WHP) running something like a Fab9 EFR turbo on a 2500 cc engine, the drop is an ASTRONOMICAL 50-60%!!! This means as you progress down the row of cylinders from front to back, each cylinder is running with less and less fuel. This is a BAD situation! This can lead to your front cylinder running much richer than each progressive cylinder, with the rear most on the rail running dangerously lean.
The why, you ask, am I seeing a decent AFR reading from the front air fuel sensor (Front O2)? The answer is simple, the O2 sensor takes an average of all 4 cylinder ratio outputs. To further prove this, we installed 4 pyrometer couples in the headers of our test cars, and as shown in the fuel pressure testing, each cylinder front to back was reading leaner and leaner.
In the past, the solution to this issue was to simply install a higher output fuel pump in the tank. Higher volume= higher rail pressure under load, simple right? Problem is, you still have the drop of volume front to rear because the rail itself is a fixed volume! Lower volume= lower available fuel pressure at the injector again! And while this works, it has a serious drawback; if you are running a 12:1 shown AFR under load, you are actually getting the average across all 4 cylinders, So your #1 cylinder may be actually running at 10:1, while the #4 cylinder is showing 13.5:1. Again, bad situation!
So to solve this, we came up with a simple return system we call the FULL FLOW RETURN SYSTEM. Its not a new idea by any means, and in fact was common practice in early Fuel injection systems. But its beauty is in the simplicity of its design.
With our FULL FLOW system, fuel is supplied to the rail as it would be with the stock system, but a return is added to the system, with a post rail regulator, that allows full, and complete filling of the rail, and the correct volume to each injector. So pressure at any point in the rail is the same as any other point! This allows each injector to have the volume it requires to perform as required. This results in more even cylinder performance, and more even cylinder to cylinder exhaust temps.
Our kit is provided with all required stainless braided hoses, fittings, and hardware, as well as a very well written step by step instruction manual. The installation can take less than 4 hours using hand tools and a drill. We offer several options on fuel pumps, and hose sizes, however the standard option kit is well suited for the average low output turbo 2.0.
In order to make these kits, we have to modify the factory fuel system components. To make the process painless for the customer, we have the kits pre built on the shelf. However to insure that we always have enough factory parts to modify, we are charging a core deposit on the fuel pump assembly, and the factory fuel rail. To that end, once you order, the kit will be sent out with your specs(pump type, hose size), and a core deposit is charged with the initial order. Once you return the rail and pump housing, we will refund the core deposit to your card( or paypal if you prefer)