One aspect of the 96-98 head-intake combo that 'seemingly' limits its performance is that fuel is injected into only a first one of the dual runners (i.e., a primary runner) for delivering the air-fuel mixture to the corresponding cylinder. A second one of the dual runners (i.e., a secondary runner) delivers air, without the addition of fuel, to the same cylinder. Accordingly, it is necessary for raw air from the secondary runner to be mixed with the air-fuel mixture of the primary runner within the cylinder. This is a less than optimal approach to achieving a desired a/f mixture within the cylinders.
It should be noted that the port dividers in each bank of the 96-98 intakes are not aligned symmetrically with the runners of the heads or the runner passages of the IMRC plates. The port divider of the runner pair at the front of the intake is skewed at a different angle than the port divider of therunner pair at the rear of the intake. The port dividers of each bank of the intake are at slightly different angles to accommodate the air horn bosses of the intake being more closely spaced together than the ports in the heads. The intent of removing the port dividers is to provide more uniform air flow between cylinders and to eliminate the flow discontinuity associated with the port dividers. By modifying the IMRC plates to include the port divider lead-in, better uniformity is provided as the IMRC runner passages are symmetric with the runners in the heads.
When evaluated, the intake resulted in very poor driveability (e.g., poor throttle response and massive hesitation in low-rpm transient throttle conditions). It is believed that the orientation of the injector, rather than its absolute position, hindered proper fuel atomization/deliver into the cylinders. Due to space constraints, the injectors had to be orientated in a position wherein the fuel spray was directed across the air stream rather than essentially parallel with it (i.e., aimed toward the back of the valves). This resulted in fuel puddling and lean/rich conditions. At high engine and road speeds (i.e., full throttle in 3rd and 4th gear between 6000 -7400 rpm), the car 'felt;' very strong. However, driveability made the car difficult and dangerous to drive, so a more complete evaluation was not attempted.
Single pintle and disk type injectors were evaluated. Neither type of injector provided any appreciable difference in driveability over the other.
Thanks to assistance from Chris Mureen (aka Chris98Vobra), various modifications to some lesser known/used PCM parameters were made possible. Examples of the parameters modified includes parameters relating to injector delay relative to piston location and parameters relating to fuel puddling/atomization. Unfortunately, none of the PCM modifications resulted in any appreciable improvement in driveability.
Lastly, the port region of the intake adjacent to each relocated injector was modified with epoxy in an attempt to improve air flow characteristics in this region of each runner. The combined volume of the primary and secondary ports in the 96-98 heads/IMRC plates is considerably greater than the volume of the air horns. Accordingly, there is an area of less than optimum flow between the air horn and the IMRC plates, particularly once the port divider is removed. While the use of epoxy to enhance transition of airflow from the air horns into the primary/secondary runners enhanced driveability quite dramatically improved, driveability was still entirely unacceptable.
See the Dividerless Intake Prototype section below for details on the epoxy fillers formed for improving airflow transition from the air horn into each of the dual runners of the heads.
This prototype intake has provided exceptional driveability, without any unusual tuning required. This confirmed speculation that the injector location/orientation was hindering driveability. As for performance gains, there 'seems' to be an improvement in how hard the car pulls through 7K rpm and up to about 7400 rpm. Development of this prototype is on-going. Once a few more 'enhancements' are made, this intake will be dynoed back to back with a SSR Stage I intake.
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