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Subaru Impreza GX to a 1UZ V8 build

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Hi all, just joined the forums as I have a project underway which may need some assistance from some other Scooby owners... I bought a LS400 with a 1UZ-FE for £400 around a year ago, has about 240k miles on the clock I believe... The engine runs really sweet and its purpose has been yet to be determined til today when I went to view a Subaru Impreza GX, the car is from 2003 has 97k on the clocks, a couple marks here and there but is in very good overall condition except that the engine is knocking and its very bad.




Hopefully get the engine out the LS400 soon and same goes for the subaru... I would like to keep the AWD system but im sure that means using an STI drivetrain...


If there's any advice then feel free to let me know as its all appreciated, I will try to keep updating on this project and may ask some questions along the way.

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Hi n welcome. 

Sounds like a interesting project 😎

I'd imagine you'd need a bug onwards sti 6 speed to cope with the power a v8 would push out .As the bug onwards 5 speeds are at their limit at about 350hp ish .

6 speeds are a straight swap using the 6 speed box ,box cradle ,gearstick/linkage and prop . If you use the same ratio 6 speed you can retain the rear diff from the 5 speed but thats in turbo versions and I'm unsure what differences between those and na diffs tbh .

Are you intending on using the v8 ecu and splicing the v8 loom into the gx loom ? 

As electrics isn't my forte and I'm curious as to how your gonna get the extra cylinders firing and fueling .


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Yeah we're going to be essentially running the V8 ecu for all things engine related then the GX loom can just look after itself good enough, the ecu should just look after the extra cylinders and if it comes to it we can take the fuel system and pump from the Lexus which the engine came from and use that instead of the subaru system.

I am going to need to replace many parts of the car for STI versions since I very much doubt the GX parts will take any of the power, anyone know what kind of parts? I was thinking STI gearbox and STI rear diff, drive shaft e.t.c. however we will be supercharging this car one day to upwards of 500hp, would the STI kit take this power if not then what max HP can them components take?


If anyone has any gearbox codes for the 6 speed strongest boxes that would help, in the meantime im going to keep on googling lol.

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The 6 speed sti box's have been known to handle over 700hp but you'd need to fit the r180 hubs and diff as well as the 6 speed box and bits i listed earlier .

You might also need the rear diff carrier /subframe ,arbs and arb brackets .

Obviously suspension and brakes will also need to be upgraded,  so maybe a donor bug onwards sti with crash damage or a blown engine might be worth looking into . As the 6 speed ,rear diff ,hubs ,driveshafts ect will cost £2.5k + alone let alone suspension, brakes ect  

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