Original poster:2gGSX [blockquote][blockquote][blockquote][blockquote] Controlling the extra fuel:[/blockquote][/blockquote][/blockquote][/blockquote]

Pumps: for a pump above a Walbro 190 (or equivalent pump, such as the stock RX7 pump), it is highly recommended that you use an aftermarket AFPR to control your fuel pressure. While some people will argue that they do not have FPR overrun, they most likely do but do not care since they do not have that many problems with it. If you want to do things the right way, get an AFPR with your new Walbro 255hp.

Injectors: there are a plethora of options available for controlling your injectors. They range from the lower end SAFC/logger (or MAFT) to a standalone system like an AEM EMS or a Haltech. Thus I’ll try to break them down to make a selection simple.

SAFC/logger: this is the simplest method of controlling injectors. It operates by tricking the ECU into seeing less air than there actually is, thus reducing the fuel the ECU puts in. The logger is used to view the effects of your changes. 1g’s can tune for zero knock while 2g vehicles can only tune by their timing curve (and to a lesser extent O2 values, which is relatively worthless). The maximum controllable injector size with a SAFC is generally agreed to be ~650 cc/min injectors. The problem with using a SAFC to do this is that you remove so much airflow signal that the ECU will add a lot of timing which in combination to high boost and actual airflow will result in knock and create a tuning hell. Thus, I would recommend (you and others may choose to do otherwise, this is simply a suggestion) that the highest injector size you control with a SAFC is 550 cc/min.



MAFT/logger: this system operates the same as the SAFC in that it hides visible airflow to the ECU. The benefits include some increased airflow, a minor decrease in spool time (mostly unnoticeable), and the ability to vent the BOV in blow through mode. Since the MAFT operates in the same way as the SAFC, the note I wrote above about excess timing with large injectors applies as well.


To run 650 cc/min or bigger injectors without the associated problems of a SAFC or MAFT you will need to use a chip of some sorts (or a standalone). Thus:



Chip: examples are the Keydiver chips or DSMLink. These support changes in the actual fuel maps that the ECU sees as well as changes in deadtime and global due to larger injectors. Thus, with a SAFC or MAFT I would recommend a Keydiver chip to run large injectors.



DSMLink: this is the medium between a piggyback like the SAFC and a standalone like an AEM EMS. This is a great system and choice of many people. More information can be found at www.dsmlink.com


Standalone: AEM EMS, Haltech, etc. If you are looking at these then you probably do not really need this guide. If you are looking at these and don’t understand most of this guide, you probably should look at something else. For anyone curious, these allow you to fully customize every aspect of your car (literally, everything). Most people will spend more time setting the car up to idle at 700 RPM than tuning for WOT performance.

[blockquote][blockquote][blockquote][blockquote][blockquote]Common problems:[/blockquote][/blockquote][/blockquote][/blockquote][/blockquote]


High IDC: the most obvious way to fix this is to upgrade to larger injectors. Sometimes however, this is annoying if you run a SAFC and need a little more fuel, but don’t want to upgrade to 650cc injectors and have the extra problems. In this situation, you can look at upping your base fuel pressure. Fuel flow of injectors can be calculated by the equation:

Flow = (Injector Size)(New Base Pressure/Old Base Pressure)^.5

For example, if you are a 2g (base pressure = 43 psi) with 450cc injectors and want to raise your base fuel pressure to 48 psi, then the new flow of your injectors will be (450)(48/43)^.5 = 475.44 cc/min. It is very important to note that you should not increase your fuel pressure too much as this will cause fuel to possibly shoot past the rings and cause you to throw a rod (engine oil and fuel don’t lubricate quite as well as just engine oil).
[blockquote][blockquote][blockquote][blockquote][blockquote][blockquote]Tuning[/blockquote][/blockquote][/blockquote][/blockquote][/blockquote][/blockquote]

This is not a definitive tuning guide, so the best chance you have is to read more from other sources.

[blockquote][blockquote][blockquote]Buying what you need versus for the future:[/blockquote][/blockquote][/blockquote]

The mantra today is “Do it right the first time”. This is not necessarily a bad view on things—on the contrary it’s great advice from seasoned people. When this saying drives people to become massively excessive is when I believe there is a problem. If you have a stock turbo but believe that someday, just maybe, you will run a GT42R and run 9’s, so you run out and buy 1600cc injectors. Can you do this? Sure, if you can control them go for it. Is this necessary? No. If you continuously upgrade turbos every couple of months and keep getting larger then sure, maybe you should get those 1600cc injectors. If you are a common person however who will never see more than a 50-trim sized turbo then you more than likely will not need such behemoth injectors. In closing, please be realistic people, and have some common sense.