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Gen III Conversions
Phoenix Mechanical

Gen III 5.7ltr Commodore engines are becoming more available and affordable second hand, as well as new crate engines. These engines can be purchased in kit form, with all bolt-ons.

If you are going to buy the engine without a transmission, it will need to have a manual PCM and engine harness. If you don't, you WILL have problems. The transmission harness is incorporated with the engine harness. If this harness and PCM is used but not connected to a transmission, the PCM will think there is something severely wrong with the trans (because it isn't there), and a multitude of Malfunction codes will be set. When a code is set the PCM will revert to "limp home mode", meaning that only basic programmed functions will be used, until the codes are repaired/removed.

For this reason, it is important to fit a MIL (Malfunction Indicator Lamp, aka Engine Check Lamp). A MIL should illuminate when the ignition of the vehicle is on, and once the engine is started, it should go out. If it does not, there is an PCM issue that requires attention.

The OBD2 (Onboard Diagnostic) connector, should also be fitted during a conversion, so that a scan tool (Holden or Generic) can be plugged to it, to check PCM functions and codes.

Automatic PCM's and wiring harnesses can be made to operate without being connected to an automatic transmission, but the process is a lot more involved.

P.S. Ensure that the wiring loom and the PCM matches the engine and gearbox you purchase.


There can never be enough planning. Too often things are overlooked, and budgets blow out. Here is a brief outline of components to plan for, and some questions, but each conversion would need specific requirements, and not every situation or combination is listed in the possibilities mentioned below.


* Engine Mounts - Will the mounts be durable, and are they readily available if the fail?

* Adapter plate/Bell housing - These are commonly used in 4WDs, where the original 4WD gearbox and transfer case is maintained.

* Adapter flywheel and clutch - Also applies to 4WDs.

* Starter motor - Again for 4WDs.

* Sump and pick-up - Gen III's have an alloy sump, and are not easily modified. Several variations are available from american versions.

* Exhaust manifolds/Extractors - Will the standard manifold fit the application and allow engine pipes to be made? Are extractors available to simplify this? Where will the catalytic converter be fitted?

* Air conditioning - Will you want air conditioning? Will the air conditioning compressor fit in its original location? Does the vehicle have air conditioning already? Can lines be made up to adapt the Commodore compressor to the vehicles system? Is there enough room?

* Power steering - Gen III's use a serpentine engine belt which incorporates the power steering pump. If the power steering pump is not needed, this will need to be addressed. If the power steering pump is used, high and low pressure lines will need to be made.

* Radiator - Where are the inlet an outlet positions of the radiator when compared to the V8's requirements. Is the original radiator large enough? Can the inlet and outlet of the original radiator be modified to suit the V8. What hoses will be needed. Is there an overflow bottle system? What about the heater hoses and heater tap?

* Engine fan - Will it fit? Is there enough room for a shroud? After market thermo fans can go either on the front or the rear of a radiator, as the blades are usually reversible.

* Accelerator cable - Is one available to suit, or who can make one?

* Fuel pump - EFI Fuel pumps located near the fuel tank (rear of vehicle) are known as a push pump. This style of pump needs to be gravity fed, as they are predominantly designed to push fuel, not to pull. For the pump to be durable, it needs to have an adequate supply. Several possibilities are available, depending on usable room, size of the pump, size of the sender unit and mounting hole (if an internal pump is to be fitted), etc. This is usually one of the areas most overlooked, and can often result in premature fuel pump failure.

P.S. Don't forget about a fuel filter!

* EFI return line - If the vehicle was carbureted before the conversion, chances are there is only one fuel line coming from the fuel tank. The EFI system will require another line to be run back to the fuel tank (from the fuel pressure regulator on the right side of the fuel injector rail) and be of the same size (5/16) as the supply line.

* Pollution Canister (aka carbon canister) - Usually required by law. Either 1 or 2 ports (depending on model) on the throttle body will be for the canister. The canister will also require a vent pipe, which usually runs back to the fuel filler neck in Commodores.

* ULP fuel filler - Laws require that an engine that is designed to run on Unleaded Fuel must have an unleaded fuel filler neck (smaller hole with a spring loaded flap) to comply with ADR's.

I find this very odd now, seeing that leaded petrol is no longer available. Previously, the change was required so that leaded fuel spouts would not fit into the fuel tank opening, but now that leaded petrol is not available, it seems pointless. I would suggest that you check with the state laws that apply to you, because as far as I know, South Australians are still required to change the filler neck!

* Speedo Sensor - Even though the gearbox has not been changed, the PCM will require a speedo signal to help maintain and control idle during deceleration. Speedo adapters are available.

* Wiring - It's not just a matter of a couple of power and earth wires. As the models progress, so does the intricacy of the wiring. Even though the wiring requirements are straight forward, it's amazing the amount of cars we see that haven't been fully wired, and don't even have a MIL.

* Air box/Air cleaner/Air intake - Usually the easiest way is to either use the standard air intake and air filter box, or a pod.

* Check your state's legal requirements to ensure your components and conversion complies.

Engine and Transmission Conversion

* The above listed plus;

* Gearbox mount and/or cross member - some conversions only require the rubber mount to be changed, some require a cross member as well.

* T-bar shifter rod/Gear stick hole plate/Console - Whether it's a manual or an auto, your going to need the hole in the floor for the shifter (cable or mechanism, depending on style choice) to mount to, or the gear stick to protrude through. Many people opt for an aftermarket shifter, like a B&M or a Hurst shifter, but not all aftermarket shifters meet ADRs (Australian Design Rules).

* Tail shaft - Is one available? Will a different model fit? Can yours be modified? At the end of the day, tail shafts can be custom made, it's just another cost to be aware of!

* Trans cooler - This is always a good idea for any automatic transmission, and eliminates the need for an automatic radiator if the vehicle was a manual.


When we buy an engine for a conversion, there are items we expect to be included when buying in "kit" form. That does not mean that the supplier agrees, but this needs to be sorted out before the final purchase price is agreed upon! Below is a run down of what we would want for a "normal" V6 conversion.

1. A Long dressed engine. Meaning that the engine has not been unsealed. Eg; Rocker covers, inlet manifold assembly, throttle body, sump, water pump and harmonic balancer are still attached.

P.S. A short motor refers an engine without heads. A long motor refers to an engine with heads.

2. Engine mounts and brackets (may not be needed but it's easier if they are there, that way you get the bolts as well).

3. Flywheel or Ring gear, with associated bolts.

4. Starter motor and bolts.

5. Alternator.

6. Power steering pump with high and low pressure lines (lines can be modified).

7. Distributor and coil (leads aren't that important, because new ones are usually a good idea).

8. Exhaust manifolds, front engine pipe, O2 (Oxygen) sensor/s and catalytic converter. Make sure the exhaust manifolds aren't cracked (mainly VN and VP RH).

9. Battery harness, complete and undamaged.

10. Engine harness, complete and undamaged.

11. ECM/PCM with memcal (to suit the engine).

12. Pollution canister, bracket and vacuum pipes to the inlet manifold.

13. Accelerator cable to suit the engine (cables can be modified).

14. Radiator hoses, heater hoses and heater tap. They may not be needed, but they can make good templates.

15. Thermo fan (if needed).

16. Bolts. Make sure you get the bolts/nuts for any items that aren't on the engine. Like bell housing bolts!

Like I said above, what comes with a "kit" may vary from supplier to supplier. Make sure you clarify what you need before you buy!


If needed, we can help with other items that may be needed for a V6 conversion.

* Security cleared memcals.

* Modified memcals.

* Conversion wiring kits.

* Engine wiring harnesses (second hand, new and NOS. Availability does vary).

* Battery harnesses (second hand, new and NOS. Availability does vary).

* ECMs and PCMs.

* Speedo adapters.

* Custom wiring looms.