While reversing the 12588500 OS was the core of the project, a lot of custom hardware work went into making the car itself functional. This section covers the physical problems I ran into during the build and the custom work I had to do to get everything working together. From sensor wiring to mechanical fitment, nothing went in without needing to be adapted, relocated, or reworked. This was not just about getting the PCM to log clean data. It was about making the entire system work as one.
The narrowband O2 sensor was not accurate enough for tuning. I installed a wideband O2 sensor and controller, which required clean power and a usable output signal for the PCM. I wired the controller’s power through a relay connected to a switched twelve volt source so it would only run when the engine was on. The analog signal was then routed into the EGR input pin on the PCM, which I confirmed could read analog voltages. This setup gave me consistent wideband AFR data during tuning.
I modified the exhaust by installing aftermarket headers, which changed the position of the O2 bung. The original bung location was too far downstream and caused turbulence, making the wideband readings inaccurate, and also ran into clearance issues with the firewall. I had to cut and relocate the bung to the other side of the collector, which solved both the clearance and signal quality problems. Early attempts to weld the stainless bung into place failed because my welder was not capable of handling stainless steel.
The Eaton Gen 5 M90 supercharger I installed did not support the factory EVAP layout. The original design placed the purge solenoid directly into the back of the supercharger case, but this location had no clearance with the new throttle body and adapter. To fix this, I reused the EVAP solenoid from the stock Gen 3 supercharger. I tapped a new hole into the back of the Gen 5 case and threaded in a brass hose barb. I then ran a vacuum line from the Gen 3 solenoid to the new fitting. During this process I filled the case with metal shavings and had to fully disassemble and hot tank the supercharger. I also stripped one of the bolts during reassembly and had to replace it before reinstalling the unit.
When I installed a cold air intake box and upgraded to an LQ4 MAF sensor, I ran into wiring issues. While there are adapter harnesses available that match the LQ4 plug to the factory harness, they were too large to fit through the small wiring hole in the airbox. To work around this, I bought a 3 pin throttle position sensor extension, cut it in half, and used it to bridge the connection. I wired one end to the original MAF sensor wiring on the car’s harness, and the other end to the adapter harness going to the LQ4 MAF. The extension cable was small enough to route cleanly through the airbox hole without needing to drill or modify the intake box.
The replacement engine I found came out of an H body car, but mine is a W body. While they are the same engine block, there are a lot of small differences between the two. I had to pull several components off the original engine and move them onto the new one to make everything fit and line up. Brackets, sensors, oil pan, and accessory mounts were all slightly different. Without the original engine as a reference and donor, the swap would not have worked.
This section documents the current state of the car beyond what was required for PCM reversing. These modifications support performance, reliability, and long-term tuning flexibility. The goal of this build was to dramatically improve airflow and reduce intake temps while staying in a power range that would not risk damaging the stock transmission.
ZZPerformance Cold Air Intake
Sealed airbox drawing cool air from the fender well.
GM LQ4 MAF and IAT Sensor
Higher resolution MAF for more accurate airflow tracking under boost.
Cadillac Northstar Throttle Body
Much larger than stock, improves throttle response and flow into the blower.
Eaton Gen 5 M90 Supercharger
Swapped in for better rotor design and lower outlet temps, Eaton reports up to 9% greater efficiency from the Gen 3 to the Gen 5. Pulley dropped from 3.8" to 3.3".
ZZPerformance 1.9:1 Modified Rockers
Increases valve lift while keeping stock camshaft.
SLP 3800 Headers
Equal length design to improve exhaust scavenging and reduce backpressure.
160 Degree Thermostat
Lowers coolant temps to help reduce knock and support higher boost levels, especially in a hotter climate like Florida.
ARP Head Studs
Provides improved head clamping force over factory bolts.
90 Pound Valve Springs
Prevent valve float with increased boost and higher lift rockers.
Autolite AR103 Spark Plugs
Colder range plugs gapped for boosted application.
Wideband O2 Sensor
Wired to the PCM through EGR input for accurate AFR data while tuning.
Intercooler
Install a core beneath the supercharger to reduce air temps and lower chances of detonation at higher boost.