Modifications - Fuel Management
The VR4 fuel map is designed to be conservatively rich from the factory. Furthermore, during wide open throttle (WOT) conditions above 4000 RPM, the ECU literally dumps as much fuel in as the engine will take. This is less than ideal for all out performance. Fuel control is taking a step toward a more serious modification. With it you have the ability to take and otherwise reasonably well running engine and turn it into either a screamer or a useless pile off melted engine parts. It can definitely be worth the gains in terms of throttle response and power. Proceed with caution however and be sure you either have someone who can tune the fuel control device or you become well versed in the process. Fuel control is an absolute necessity once stock injectors have been replaced with larger ones. A lot of people in fact leave fuel control until this stage. However, the "right" thing to do is get what you've got working properly first. Fuel control definitely fits into this approach. You also learn to tune the car before you have a finicky 600 HP monster.
The AFC is a device which intercepts the frequency sent by the MAS to the ECU and allows adjusting it upwards or downwards across 5 RPM ranges. Adding to the air signal sent to the ECU causes the ECU to believe more air is flowing than actually is passing through the MAS. It responds by adding more fuel thus enrichening the mixture. The converse is true for reducing the airflow signal to the ECU. The AFC can work well for many situations. It has one large drawback, however. The adjustment is based on RPM. Airflow changes more closely with engine load than RPM. The AFC is really only useful for WOT tuning and even then it is a stop-gap measure at best as it is not sufficient for upgraded injectors.
Apex'i Super AFC
HKS Vein Pressure Controller (VPC)
The VPC eliminates the stock MAS vortex style airmeter and replaces air flow determination with a manifold absolute pressure (MAP) system. MAP systems read the pressure in the intake manifold and combined with engine RPM calculate an estimate of engine load. It is reasonably precise and many fine engine management systems are MAP based. The reason for the VPC in the first place had more to do with the lack of availability of replacement less restrictive airmeters than the superiority of MAP. The VPC can be used with stock or 550cc injectors with the change of a chip. Success has been realized with even larger injectors but a custom chip may be required. Chips are specific to California cars, 49-state cars, and injector size. Success with the VPC depends greatly on other modifications such as fuel pressure, fuel pump and injector bahavior.
This unit is similar to the AFC. It provides a adjustment of individual RPM ranges as well as overall gain. The GCC has an interface that connects directly to the VPC for an integrated solution.
An alternative to replacing the stock injectors with larger ones when more fuel is required is installing additional injectors. The stock ECU of course has no means of controlling such additional injectors. A piggy-back fuel computer such of the HKS AIC can control the secondary fuel map introduced by additional injectors.
The Rebic is an additional injector controller that supports up to 8 additional injectors.
Basically a logging device for the Rebic III providing additional control over the secondary fuel map.
The Mass Airflow Sensor Control/Conversion (MASC) from Team Rip Engineering is a two part solution to the fuel control issue. The heart of the system is a computer which allows adjustment of the airflow seen by the ECU. Airflow is adjustable +/50% in 10% increments across available airflow. Furthermore there is an overall main gain which adjusts the entire map +/-50%. Up to three maps may be stored and retrieved at any time. The MASC also provides monitoring of exhaust gas temperatures (EGT), boost, oxygen sensor voltage and injector duty cycle (IDC). The second optional part of the MASC is an 83mm hotwire airmeter. Airmeters are extremely accurate and furthermore they can deliver actual airflow to the ECU, not a derived or calculated quantity. The stock MAS becomes too restrictive as it approaches the 500 HP mark. Above certain airflow volumes it severely loses accuracy. A properly sized hotwire airmeter can be no more restrictive than a MAP based system yet yield the same accuracy of the vortex style MAS. The TRE MASC airmeter is huge and comes fitted with a large K & N reusable oiled foam air filter.
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