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Gemini EFI Fuel Injection Kits

Starting from $1025 

Bolt on kit designed for an Isuzu G series SOHC engine (G161, G180, G200) within a Holden Gemini, models TX-TG, but could easily be used in the engine bays of a Jackaroo, Rodeo, etc.  Obviously, it will also bolt onto 4Z series engines.

The inlet manifold used is a factory Isuzu manifold as fitted to 2.6 litre engines and is modified to bolt onto a G series SOHC engine.  The manifolds do not simply bolt up to a G series engine without modifications. 


The kits come with everything needed - it is a complete bolt on kit designed to include every component needed to fit the EFI manifold to the engine and install the complete fuel injection system minus the EFI computer.  The kit comes will all the little parts like gaskets, hose clamps, studs, etc.  There is no fabrication necessary, it is truly a bolt on EFI kit.  The only extra work required is to hook up an air filter, wire up an EFI computer and then tune to suit your engine.



The kit consists of:



The EFI manifold is quite large, using 36mm ID inlet runners, and approx. 2 litre plenum.  The manifold can flow enough air to support well over 450 horsepower.  The injector size is the only limiting factor, but bigger injectors are easily installed.  The manifold is larger internally and can flow more air than a standard Piazza turbo manifold.


The manifold is modified to directly bolt onto the Gemini cylinder head.  All unnecessary ports are plugged, while a few are left available for things like MAP sensor, brake booster and boost gauge connection.



Depending on type of manifold purchased, either an oval shaped twin butterfly TB is used, or a big single butterfly Hitachi throttle body, 60mm in diameter.  Throttle position sensors (TPS) with switches for closed throttle, open throttle, and wide open throttle are included with either TB type.



These manifolds are fitted with fairly big Nippon Denso injectors.  

Oval TB EFI kits are fitted with 300cc injectors. 

Round TB EFI kits are fitted with 330cc injectors.

Injectors are sonically cleaned and flow tested, so you will get a set of matching flow injectors.


As an example, the 330cc injectors are rated at 44psi fuel pressure with the standard regulator.  330cc will be enough fuel delivery for around 240hp.  Upping the fuel pressure to 59psi (4bar) would make the injectors flow more like 390cc and be capable of handling around 280hp.  


Even bigger injectors such as 550cc Mazda 13BT units can be installed very easily to the manifold, and I have done this conversion myself several times.  The manifold can flow enough air to support around 400-500hp, so if you plan massive power for the future, all that would need upgrading is the injectors, the rest of the manifold assembly would still handle the power.


The fuel pressure regulator also works very well as a boost referenced regulator for turbo applications, as I am using the stock regulator on my turbo engine.  The regulator gives a 1:1 rate of fuel pressure rise, so approximately 1psi of fuel pressure increase for every 1psi of turbo boost pressure.  A common misconception is that you need a rising rate regulator for a turbo engine, this is not the case.  A rising rate regulator may actually be costing you horsepower if its stressing your fuel pump unnecessarily.



The standard sensors include the throttle position sensor (TPS) and the water temp sensor designed for use with an EFI computer.  The TPS has the typical closed and open throttle switches, and also has a wide open throttle feature, great for water injection, a boost solenoid, NOS, intercooler spray, etc.  Whatever you can think of.


The wiring loom provided has the 4 Denso injector plugs, the TPS plug and the water temp Bosch style plug, all on a short (0.5m) flying loom ready to hook up to the EFI computer of your choice.



The fuel system included a BRAND NEW Bosch style external EFI fuel pump.  The fuel pump is a Bosch 070 VL turbo spec pump.  The pumps can handle around 350hp worth of fuel delivery, so should exceed your engine output with standard injectors, with a bit left up its sleeve.  Included are adaptors required to connect from the stock Gemini electric fuel pump and from the stock steel fuel line to the inlet of the manifold fuel rail.  


New high pressure hose is included to connect from the pump to the stock steel fuel lines.  Wherever there is low pressure hose from the stock carby system that now has high pressure fuel in it gets replaced by the high pressure hose.  Enough hose is included to do the whole car, along with all the required hose clamps.  Included high pressure hoses to join stock Gemini pump outlet to fuel line adaptors, then to EFI pump, hose to replace low pressure hose under car/over diff, and to connect fuel supply and return lines of EFI manifold and fuel filter in engine bay.


A new EFI filter is also included to keep the injectors and the rest of the fuel system clean from debris.  You cannot use the standard carby filter due to the higher pressure of the EFI system.



The fitting kit consists of an accelerator cable which is another part that's often overlooked when people buy standard manifolds and try to adapt them to the Gemini.  The accelerator cable is modified to fit into the Gemini firewall and attach to the accelerator pedal.


New heater hose joiners and extra heater hose is included to bypass the inlet manifold self heating system and to maintain correct operation of the Gemini coolant and heater system.


New gaskets are also provided to bolt the inlet manifold onto the Gemini cylinder head.  



So in summary, each kit option comes with the following hardware/accessories assembled ready for use:


EFI manifold 

+ Complete & assembled EFI manifold with 36mm inlet runners.

+ Big 60mm throttle body (optional oval twin butterfly TB).

+ Large plenum chamber with all unnecessary ports blocked.

+ 300cc or 330cc fuel injectors - sonically cleaned and match flowed (optional 300cc injectors or 460cc injectors)

+ Fuel rail and boost/vacuum referenced fuel pressure regulator.

+ Throttle position sensor including wide open throttle switch, EFI water temp sensor.

+ Wiring loom for all sensors and injectors.

+ Accelerator cable to suit EFI manifold into Gemini engine bay.

+ New inlet manifold gaskets.

+ New heater hose joiner kit for manifold to heater hose connection


EFI fuel system

+ New Bosch 070 VL Turbo spec EFI fuel pump, capable of supporting over 350hp.

+ New brass adaptors from stock Gemini fuel hoses to fuel pump inlet/outlet.

+ New brass adaptors from stock Gemini hoses to high pressure fuel line.

+ New EFI fuel filter.

+ All high pressure fuel lines and hose clamps required to fit up high pressure fuel system to whole car.


Complete fitting instructions

Simple to follow fitting instructions that guide you through the installation.  Note: The manifold is supplied assembled and ready to bolt on.  Instructions cover fit up of fuel lines, heater hoses, and also the electrical connection of the wiring loom.


Cost is $1025.00 plus postage - Oval twin butterfly throttle body


Cost is $1095.00 plus postage - 60mm single butterfly round throttle body


Email us with your post code for a postage quote.  Also ask for pricing on 460cc or 550cc Mazda RX7 fuel injector upgrade.  If you want any more info feel free to ask questions at sales@turbogemini.com


As can be seen in the photos, we piece these kits together ourselves and know the condition of all components.  Where possible, components have been disassembled, inspected, cleaned, and then reassembled.  The injectors are sonically cleaned and flow benched so you get a set of matched injectors.  The EFI manifolds are usually filthy when we get them and many hours are spent stripping and cleaning everything and modifying the manifolds so they slip straight on.  When we're finished, they are in near new condition.  Usually the manifolds show either zero or very minor corrosion in the water cooling galleries.


The following photos show the components in the kit, and one of the manifolds fitted to an engine to show how it all fits together.