XJ6 & XJ12 Series I, II & III 1968-1992

XJ12 Rb25DET Conversion

Old 03-04-2019, 09:32 AM
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Default XJ12 Rb25DET Conversion

What's going on everyone, my R34 was written off not that long ago and in my search for a rolling shell I have come across a rather clean Series II XJ12 shell. I'm looking to engine swap my RB25DET making roughly 500rwhp (370rwkws) on 21PSI of boost & E85 into this shell. Does anyone have any experience with this kind of build?

I've poured close to 15k into my engine on the R34 and as much as I love them, it's time to make a change in what I am doing, however would like to get an idea as to what I am getting myself into before I dive straight in. The mechanics side of things is the easy part, My main concerns are about how the motor will line up with the rest of the shell and if the shell will comfortably hold that much power & more. Obvious suspension work will need to be done as the shell is completely stock.
Old 03-04-2019, 10:45 AM
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Where's the sump? I'm not familiar with your RB but as long as it rear sump it will just need basic fab to set in there. I've got a SBC with similar HP and the rear suspension mods to handle that amount of power are extensive. There is no upper control arm on the rear spindle and it move around under power. The hit from a turbo will only make that worse. There is also limits to rear tire size with out metal work.

Also the RB is a Rev'r not ideal for a heavy XJ. Plan on doing lots of weight management. I'm working on getting my XJ down to 3600 Lbs this week, I'm at 3700 and the mods are extensive.

Look up my 2015 and 2017 coupe projects. You will see the mods necessary to prevent these car from twisting under power.

My first XJ project with 400 flywheel HP and no chassis mods would auto change lanes on the highway under power.
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Old 03-04-2019, 03:05 PM
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Thanks for that, I'll have a look

It is a rear sump so that sounds like it'll work fine, but the shell twisting is my main concern
Old 03-31-2019, 04:28 AM
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Sounds like an interesting swap to me

could you look into what Broadspeed done with their XJ12 race cars back in the day, although not competitive at the time due to weight compared with the competition
Old 03-31-2019, 12:47 PM
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some well placed roll bars, and serious reinforecment inside rocker areas.
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